Table Of Contents
ip drp authentication key-chain
ip icmp rate-limit unreachable
ip tcp compression-connections
show ip tcp header-compression
IP Services Commands
Use the commands in this chapter to configure various IP services. For configuration information and examples on IP services, refer to the "Configuring IP Services" chapter of the Cisco IOS IP and IP Routing Configuration Guide.
access-class
To restrict incoming and outgoing connections between a particular virtual terminal line (into a Cisco device) and the addresses in an access list, use the access-class line configuration command. To remove access restrictions, use the no form of this command.
access-class access-list-number {in | out}
no access-class access-list-number {in | out}
Syntax Description
Defaults
No access lists are defined.
Command Modes
Line configuration
Command History
Usage Guidelines
Remember to set identical restrictions on all the virtual terminal lines because a user can connect to any of them.
To display the access lists for a particular terminal line, use the show line EXEC command and specify the line number.
Examples
The following example defines an access list that permits only hosts on network 192.89.55.0 to connect to the virtual terminal ports on the router:
access-list 12 permit 192.89.55.0 0.0.0.255line 1 5access-class 12 inThe following example defines an access list that denies connections to networks other than network 36.0.0.0 on terminal lines 1 through 5:
access-list 10 permit 36.0.0.0 0.255.255.255line 1 5access-class 10 outRelated Commands
access-list (IP extended)
To define an extended IP access list, use the extended version of the access-list global configuration command. To remove the access lists, use the no form of this command.
access-list access-list-number [dynamic dynamic-name [timeout minutes]] {deny | permit} protocol source source-wildcard destination destination-wildcard [precedence precedence] [tos tos] [log | log-input] [time-range time-range-name] [fragments]
no access-list access-list-number
Internet Control Message Protocol (ICMP)
For ICMP, you can also use the following syntax:
access-list access-list-number [dynamic dynamic-name [timeout minutes]] {deny | permit} icmp source source-wildcard destination destination-wildcard [icmp-type | [[icmp-type icmp-code] | [icmp-message]] [precedence precedence] [tos tos] [log | log-input] [time-range time-range-name] [fragments]
Internet Group Management Protocol (IGMP)
For IGMP, you can also use the following syntax:
access-list access-list-number [dynamic dynamic-name [timeout minutes]] {deny | permit} igmp source source-wildcard destination destination-wildcard [igmp-type] [precedence precedence] [tos tos] [log | log-input] [time-range time-range-name] [fragments]
Transmission Control Protocol (TCP)
For TCP, you can also use the following syntax:
access-list access-list-number [dynamic dynamic-name [timeout minutes]] {deny | permit} tcp source source-wildcard [operator [port]] destination destination-wildcard [operator [port]] [established] [precedence precedence] [tos tos] [log | log-input] [time-range time-range-name] [fragments]
User Datagram Protocol (UDP)
For UDP, you can also use the following syntax:
access-list access-list-number [dynamic dynamic-name [timeout minutes]] {deny | permit} udp source source-wildcard [operator [port]] destination destination-wildcard [operator [port]] [precedence precedence] [tos tos] [log | log-input] [time-range time-range-name] [fragments]
Syntax Description
access-list-number
Number of an access list. This is a decimal number from 100 to 199 or from 2000 to 2699.
dynamic dynamic-name
(Optional) Identifies this access list as a dynamic access list. Refer to lock-and-key access documented in the "Configuring Lock-and-Key Security (Dynamic Access Lists)" chapter in the Cisco IOS Security Configuration Guide.
timeout minutes
(Optional) Specifies the absolute length of time (in minutes) that a temporary access list entry can remain in a dynamic access list. The default is an infinite length of time and allows an entry to remain permanently. Refer to lock-and-key access documented in the "Configuring Lock-and-Key Security (Dynamic Access Lists)" chapter in the Cisco IOS Security Configuration Guide.
deny
Denies access if the conditions are matched.
permit
Permits access if the conditions are matched.
protocol
Name or number of an IP protocol. It can be one of the keywords eigrp, gre, icmp, igmp, igrp, ip, ipinip, nos, ospf, pim, tcp, or udp, or an integer in the range 0 to 255 representing an IP protocol number. To match any Internet protocol (including ICMP, TCP, and UDP) use the keyword ip. Some protocols allow further qualifiers described below.
source
Number of the network or host from which the packet is being sent. There are three alternative ways to specify the source:
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Use a 32-bit quantity in four-part, dotted-decimal format.
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source-wildcard
Wildcard bits to be applied to source. Each wildcard bit set to zero indicates that the corresponding bit position in the packet's ip address must exactly match the bit value in the corresponding bit position in the source. Each wildcard bit set to one indicates that both a zero bit and a one bit in the corresponding position of the packet's ip address will be considered a match to this access list entry.
There are three alternative ways to specify the source wildcard:
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Wildcard bits set to one do not need to be contiguous in the source-wildcard. For example, a source-wildcard of 0.255.0.64 would be valid.
destination
Number of the network or host to which the packet is being sent. There are three alternative ways to specify the destination:
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destination-wildcard
Wildcard bits to be applied to the destination. There are three alternative ways to specify the destination wildcard:
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precedence precedence
(Optional) Packets can be filtered by precedence level, as specified by a number from 0 to 7 or by name as listed in the section "Usage Guidelines."
tos tos
(Optional) Packets can be filtered by type of service level, as specified by a number from 0 to 15 or by name as listed in the section "Usage Guidelines."
icmp-type
(Optional) ICMP packets can be filtered by ICMP message type. The type is a number from 0 to 255.
log
(Optional) Causes an informational logging message about the packet that matches the entry to be sent to the console. (The level of messages logged to the console is controlled by the logging console command.)
The message includes the access list number, whether the packet was permitted or denied; the protocol, whether it was TCP, UDP, ICMP or a number; and, if appropriate, the source and destination addresses and source and destination port numbers. The message is generated for the first packet that matches, and then at 5-minute intervals, including the number of packets permitted or denied in the prior 5-minute interval.
Use the ip access-list log-update command to generate logging messages when the number of matches reaches a configurable threshold (rather than waiting for a 5-minute interval). See the ip access-list log-update command for more information.
The logging facility might drop some logging message packets if there are too many to be handled or if there is more than one logging message to be handled in 1 second. This behavior prevents the router from crashing due to too many logging packets. Therefore, the logging facility should not be used as a billing tool or an accurate source of the number of matches to an access list.
If you enable CEF and then create an access list that uses the log keyword, the packets that match the access list are not CEF switched. They are fast switched. Logging disables CEF.
log-input
(Optional) Includes the input interface and source MAC address or VC in the logging output.
time-range time-range-name
(Optional) Name of the time range that applies to this statement. The name of the time range and its restrictions are specified by the time-range command.
icmp-code
(Optional) ICMP packets that are filtered by ICMP message type can also be filtered by the ICMP message code. The code is a number from 0 to 255.
icmp-message
(Optional) ICMP packets can be filtered by an ICMP message type name or ICMP message type and code name. The possible names are listed in the section "Usage Guidelines."
igmp-type
(Optional) IGMP packets can be filtered by IGMP message type or message name. A message type is a number from 0 to 15. IGMP message names are listed in the section "Usage Guidelines."
operator
(Optional) Compares source or destination ports. Possible operands include lt (less than), gt (greater than), eq (equal), neq (not equal), and range (inclusive range).
If the operator is positioned after the source and source-wildcard, it must match the source port.
If the operator is positioned after the destination and destination-wildcard, it must match the destination port.
The range operator requires two port numbers. All other operators require one port number.
port
(Optional) The decimal number or name of a TCP or UDP port. A port number is a number from 0 to 65535. TCP port names are listed in the section "Usage Guidelines." TCP port names can only be used when filtering TCP. UDP port names are listed in the section "Usage Guidelines." UDP port names can only be used when filtering UDP.
TCP port names can only be used when filtering TCP. UDP port names can only be used when filtering UDP.
established
(Optional) For the TCP protocol only: Indicates an established connection. A match occurs if the TCP datagram has the ACK, FIN, PSH, RST, SYN, or URG control bits set. The nonmatching case is that of the initial TCP datagram to form a connection.
fragments
(Optional) The access list entry applies to noninitial fragments of packets; the fragment is either permitted or denied accordingly. For more details about the fragments keyword, see the "Access List Processing of Fragments" and "Fragments and Policy Routing" sections in the "Usage Guidelines" section.
Defaults
An extended access list defaults to a list that denies everything. An extended access list is terminated by an implicit deny statement.
Command Modes
Global configuration
Command History
Usage Guidelines
You can use access lists to control the transmission of packets on an interface, control virtual terminal line access, and restrict contents of routing updates. The Cisco IOS software stops checking the extended access list after a match occurs.
Note
The following is a list of precedence names:
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The following is a list of type of service (ToS) names:
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The following is a list of ICMP message type names and ICMP message type and code names:
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The following is a list of IGMP message names:
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The following is a list of TCP port names that can be used instead of port numbers. Refer to the current Assigned Numbers RFC to find a reference to these protocols. Port numbers corresponding to these protocols can also be found by typing a ? in the place of a port number.
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The following is a list of UDP port names that can be used instead of port numbers. Refer to the current Assigned Numbers RFC to find a reference to these protocols. Port numbers corresponding to these protocols can also be found by typing a ? in the place of a port number.
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Access List Processing of Fragments
The behavior of access-list entries regarding the use or lack of the fragments keyword can be summarized as follows:
Be aware that you should not simply add the fragments keyword to every access list entry because the first fragment of the IP packet is considered a nonfragment and is treated independently of the subsequent fragments. An initial fragment will not match an access list permit or deny entry that contains the fragments keyword, the packet is compared to the next access list entry, and so on, until it is either permitted or denied by an access list entry that does not contain the fragments keyword. Therefore, you may need two access list entries for every deny entry. The first deny entry of the pair will not include the fragments keyword, and applies to the initial fragment. The second deny entry of the pair will include the fragments keyword and applies to the subsequent fragments. In the cases where there are multiple deny access list entries for the same host but with different Layer 4 ports, a single deny access-list entry with the fragments keyword for that host is all that needs to be added. Thus all the fragments of a packet are handled in the same manner by the access list.
Packet fragments of IP datagrams are considered individual packets and each counts individually as a packet in access list accounting and access list violation counts.
Note
Fragments and Policy Routing
Fragmentation and the fragment control feature affect policy routing if the policy routing is based on the match ip address command and the access list had entries that match on Layer 4 through 7 information. It is possible that noninitial fragments pass the access list and are policy routed, even if the first fragment was not policy routed or the reverse.
By using the fragments keyword in access list entries as described earlier, a better match between the action taken for initial and noninitial fragments can be made and it is more likely policy routing will occur as intended.
Examples
In the following example, serial interface 0 is part of a Class B network with the address 128.88.0.0, and the mail host's address is 128.88.1.2. The established keyword is used only for the TCP protocol to indicate an established connection. A match occurs if the TCP datagram has the ACK or RST bits set, which indicate that the packet belongs to an existing connection.
access-list 102 permit tcp 0.0.0.0 255.255.255.255 128.88.0.0 0.0.255.255 establishedaccess-list 102 permit tcp 0.0.0.0 255.255.255.255 128.88.1.2 0.0.0.0 eq 25interface serial 0ip access-group 102 inThe following example also permits Domain Naming System (DNS) packets and ICMP echo and echo reply packets:
access-list 102 permit tcp any 128.88.0.0 0.0.255.255 establishedaccess-list 102 permit tcp any host 128.88.1.2 eq smtpaccess-list 102 permit tcp any any eq domainaccess-list 102 permit udp any any eq domainaccess-list 102 permit icmp any any echoaccess-list 102 permit icmp any any echo-replyThe following examples show how wildcard bits are used to indicate the bits of the prefix or mask that are relevant. They are similar to the bitmasks that are used with normal access lists. Prefix/mask bits corresponding to wildcard bits set to 1 are ignored during comparisons and prefix/mask bits corresponding to wildcard bits set to 0 are used in comparison.
The following example permits 192.108.0.0 255.255.0.0 but denies any more specific routes of 192.108.0.0 (including 192.108.0.0 255.255.255.0):
access-list 101 permit ip 192.108.0.0 0.0.0.0 255.255.0.0 0.0.0.0 access-list 101 deny ip 192.108.0.0 0.0.255.255 255.255.0.0 0.0.255.255The following example permits 131.108.0/24 but denies 131.108/16 and all other subnets of 131.108.0.0:
access-list 101 permit ip 131.108.0.0 0.0.0.0 255.255.255.0 0.0.0.0 access-list 101 deny ip 131.108.0.0 0.0.255.255 255.255.0.0 0.0.255.255The following example uses a time-range to deny HTTP traffic on Monday through Friday between the hours of 8:00 a.m. and 6:00 p.m.:
time-range no-httpperiodic weekdays 8:00 to 18:00!access-list 101 deny tcp any any eq http time-range no-http!interface ethernet 0ip access-group 101 inRelated Commands
access-list (IP standard)
To define a standard IP access list, use the standard version of the access-list global configuration command. To remove a standard access lists, use the no form of this command.
access-list access-list-number {deny | permit} source [source-wildcard] [log]
no access-list access-list-number
Caution
Syntax Description
access-list-number
Number of an access list. This is a decimal number from 1 to 99 or from 1300 to 1999.
deny
Denies access if the conditions are matched.
permit
Permits access if the conditions are matched.
source
Number of the network or host from which the packet is being sent.
There are two alternative ways to specify the source:
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source-wildcard
(Optional) Wildcard bits to be applied to source.Each wildcard bit set to zero indicates that the corresponding bit position in the packet's ip address must exactly match the bit value in the corresponding bit position in the source. Each wildcard bit set to one indicates that both a zero bit and a one bit in the corresponding position of the packet's ip address will be considered a match to this access list entry.
There are two alternative ways to specify the source wildcard:
Use a 32-bit quantity in four-part, dotted-decimal format. Place ones in the bit positions you want to ignore.
Use the keyword any as an abbreviation for a source and source-wildcard of 0.0.0.0 255.255.255.255.
Wildcard bits set to one do not need to be contiguous in the source-wildcard. For example, a source-wildcard of 0.255.0.64 would be valid.
log
(Optional) Causes an informational logging message about the packet that matches the entry to be sent to the console. (The level of messages logged to the console is controlled by the logging console command.)
The message includes the access list number, whether the packet was permitted or denied, the source address, and the number of packets. The message is generated for the first packet that matches, and then at 5-minute intervals, including the number of packets permitted or denied in the prior 5-minute interval.
Use the ip access-list log-update command to generate logging messages when the number of matches reaches a configurable threshold (rather than waiting for a 5-minute interval). See the ip access-list log-update command for more information.
The logging facility might drop some logging message packets if there are too many to be handled or if there is more than one logging message to be handled in 1 second. This behavior prevents the router from crashing due to too many logging packets. Therefore, the logging facility should not be used as a billing tool or an accurate source of the number of matches to an access list.
If you enable CEF and then create an access list that uses the log keyword, the packets that match the access list are not CEF switched. They are fast switched. Logging disables CEF.
Defaults
The access list defaults to an implicit deny statement for everything. The access list is always terminated by an implicit deny statement for everything.
Command Modes
Global configuration
Command History
Usage Guidelines
Plan your access conditions carefully and be aware of the implicit deny statement at the end of the access list.
You can use access lists to control the transmission of packets on an interface, control virtual terminal line access, and restrict the contents of routing updates.
Use the show access-lists EXEC command to display the contents of all access lists.
Use the show ip access-list EXEC command to display the contents of one access list.
Examples
The following example of a standard access list allows access for only those hosts on the three specified networks. The wildcard bits apply to the host portions of the network addresses. Any host with a source address that does not match the access list statements will be rejected.
access-list 1 permit 192.5.34.0 0.0.0.255access-list 1 permit 128.88.0.0 0.0.255.255access-list 1 permit 36.0.0.0 0.255.255.255! (Note: all other access implicitly denied)The following example of a standard access list allows access for devices with IP addresses in the range 10.29.2.64 to 10.29.2.127. All packets with a source address not in this range will be rejected.
access-list 1 permit 10.29.2.64 0.0.0.63! (Note: all other access implicitly denied)To specify a large number of individual addresses more easily, you can omit the wildcard if it is all zeros. Thus, the following two configuration commands are identical in effect:
access-list 2 permit 36.48.0.3access-list 2 permit 36.48.0.3 0.0.0.0Related Commands
access-list remark
To write a helpful comment (remark) for an entry in a numbered IP access list, use the access-list remark global configuration command. To remove the remark, use the no form of this command.
access-list access-list-number remark remark
no access-list access-list-number remark remark
Syntax Description
access-list-number
Number of an IP access list.
remark
Comment that describes the access list entry, up to 100 characters long.
Defaults
The access list entries have no remarks.
Command Modes
Global configuration
Command History
Usage Guidelines
The remark can be up to 100 characters; anything longer is truncated.
If you want to write a comment about an entry in a named access list, use the remark command.
Examples
In the following example, the workstation belonging to Jones is allowed access, and the workstation belonging to Smith is not allowed access:
access-list 1 remark Permit only Jones workstation throughaccess-list 1 permit 171.69.2.88access-list 1 remark Do not allow Smith workstation throughaccess-list 1 deny 171.69.3.13Related Commands
Defines an extended IP access list.
Establishes MAC address access lists.
Writes a helpful comment (remark) for an entry in a named IP access list.
clear access-list counters
To clear the counters of an access list, use the clear access-list counters EXEC command.
clear access-list counters {access-list-number | name}
Syntax Description
Command Modes
EXEC
Command History
Usage Guidelines
Some access lists keep counters that count the number of packets that pass each line of an access list. The show access-lists command displays the counters as a number of matches. Use the clear access-list counters command to restart the counters for a particular access list to 0.
Examples
The following example clears the counters for access list 101:
clear access-list counters 101Related Commands
clear ip accounting
To clear the active or checkpointed database when IP accounting is enabled, use the clear ip accounting EXEC command.
clear ip accounting [checkpoint]
Syntax Description
Command Modes
EXEC
Command History
Usage Guidelines
You can also clear the checkpointed database by issuing the clear ip accounting command twice in succession.
Examples
The following example clears the active database when IP accounting is enabled:
clear ip accountingRelated Commands
clear ip drp
To clear all statistics being collected on Director Response Protocol (DRP) requests and replies, use the clear ip drp EXEC command.
clear ip drp
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following example clears all DRP statistics:
clear ip drpRelated Commands
Controls the sources of DRP queries to the DRP Server Agent.
Configures authentication on the DRP Server Agent for DistributedDirector.
clear tcp statistics
To clear TCP statistics, use the clear tcp statistics privileged EXEC command.
clear tcp statistics
Syntax Description
This command has no arguments or keywords.
Command Modes
Privileged EXEC
Command History
Examples
The following example clears all TCP statistics:
clear tcp statisticsRelated Commands
deny (IP)
To set conditions for a named IP access list, use the deny access-list configuration command. To remove a deny condition from an access list, use the no form of this command.
deny source [source-wildcard]
no deny source [source-wildcard]
deny protocol source source-wildcard destination destination-wildcard [precedence precedence] [tos tos] [log] [time-range time-range-name] [fragments]
no deny protocol source source-wildcard destination destination-wildcard
Internet Control Message Protocol (ICMP)
For ICMP, you can also use the following syntax:
deny icmp source source-wildcard destination destination-wildcard [icmp-type [icmp-code] | icmp-message] [precedence precedence] [tos tos] [log] [time-range time-range-name] [fragments]
Internet Group Management Protocol (IGMP)
For IGMP, you can also use the following syntax:
deny igmp source source-wildcard destination destination-wildcard [igmp-type] [precedence precedence] [tos tos] [log] [time-range time-range-name] [fragments]
Transmission Control Protocol (TCP)
For TCP, you can also use the following syntax:
deny tcp source source-wildcard [operator port [port]] destination destination-wildcard [operator [port]] [established] [precedence precedence] [tos tos] [log] [time-range time-range-name] [fragments]
User Datagram Protocol (UDP)
For UDP, you can also use the following syntax:
deny udp source source-wildcard [operator port [port]] destination destination-wildcard [operator [port]] [precedence precedence] [tos tos] [log] [time-range time-range-name] [fragments]
Syntax Description
source
Number of the network or host from which the packet is being sent. There are three alternative ways to specify the source:
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source-wildcard
Wildcard bits to be applied to the source. There are three alternative ways to specify the source wildcard:
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protocol
Name or number of an IP protocol. It can be one of the keywords eigrp, gre, icmp, igmp, igrp, ip, ipinip, nos, ospf, tcp, or udp, or an integer in the range 0 to 255 representing an IP protocol number. To match any Internet protocol (including ICMP, TCP, and UDP), use the keyword ip. Some protocols allow further qualifiers described later.
destination
Number of the network or host to which the packet is being sent. There are three alternative ways to specify the destination:
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destination-wildcard
Wildcard bits to be applied to the destination. There are three alternative ways to specify the destination wildcard:
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precedence precedence
(Optional) Packets can be filtered by precedence level, as specified by a number from 0 to 7 or by name as listed in the "Usage Guidelines" section.
tos tos
(Optional) Packets can be filtered by type of service level, as specified by a number from 0 to 15 or by name as listed in the "Usage Guidelines" section of the access-list (extended) command.
log
(Optional) Causes an informational logging message about the packet that matches the entry to be sent to the console. (The level of messages logged to the console is controlled by the logging console command.)
The message includes the access list number, whether the packet was permitted or denied; the protocol, whether it was TCP, UDP, ICMP or a number; and, if appropriate, the source and destination addresses and source and destination port numbers. The message is generated for the first packet that matches, and then at 5-minute intervals, including the number of packets permitted or denied in the prior 5-minute interval.
Use the ip access-list log-update command to generate logging messages when the number of matches reaches a configurable threshold (rather than waiting for a 5-minute interval). See the ip access-list log-update command for more information.
The logging facility might drop some logging message packets if there are too many to be handled or if there is more than one logging message to be handled in 1 second. This behavior prevents the router from crashing due to too many logging packets. Therefore, the logging facility should not be used as a billing tool or an accurate source of the number of matches to an access list.
If you enable CEF and then create an access list that uses the log keyword, the packets that match the access list are not CEF switched. They are fast switched. Logging disables CEF.
time-range time-range-name
(Optional) Name of the time range that applies to this deny statement. The name of the time range and its restrictions are specified by the time-range and absolute or periodic commands, respectively.
icmp-type
(Optional) ICMP packets can be filtered by ICMP message type. The type is a number from 0 to 255.
icmp-code
(Optional) ICMP packets which are filtered by ICMP message type can also be filtered by the ICMP message code. The code is a number from 0 to 255.
icmp-message
(Optional) ICMP packets can be filtered by an ICMP message type name or ICMP message type and code name. The possible names are listed in the "Usage Guidelines" section of the access-list (extended) command.
igmp-type
(Optional) IGMP packets can be filtered by IGMP message type or message name. A message type is a number from 0 to 15. IGMP message names are listed in the "Usage Guidelines" section of the access-list (extended) command.
operator
(Optional) Compares source or destination ports. Possible operands include lt (less than), gt (greater than), eq (equal), neq (not equal), and range (inclusive range).
If the operator is positioned after the source and source-wildcard, it must match the source port.
If the operator is positioned after the destination and destination-wildcard, it must match the destination port.
The range operator requires two port numbers. All other operators require one port number.
port
(Optional) The decimal number or name of a TCP or UDP port. A port number is a number from 0 to 65535. TCP and UDP port names are listed in the "Usage Guidelines" section of the access-list (extended) command. TCP port names can only be used when filtering TCP. UDP port names can only be used when filtering UDP.
established
(Optional) For the TCP protocol only: Indicates an established connection. A match occurs if the TCP datagram has the ACK or RST bits set. The nonmatching case is that of the initial TCP datagram to form a connection.
fragments
(Optional) The access list entry applies to noninitial fragments of packets; the fragment is either permitted or denied accordingly. For more details about the fragments keyword, see the "Access List Processing of Fragments" and "Fragments and Policy Routing" sections in the "Usage Guidelines" section.
Defaults
There is no specific condition under which a packet is denied passing the named access list.
Command Modes
Access-list configuration
Command History
11.2
This command was introduced.
12.0(1)T
The time-range time-range-name keyword and argument were added.
12.1(2)
The fragments keyword was added.
Usage Guidelines
Use this command following the ip access-list command to specify conditions under which a packet cannot pass the named access list.
The time-range option allows you to identify a time range by name. The time-range, absolute, and periodic commands specify when this deny statement is in effect.
A ccess List Processing of Fragments
The behavior of access-list entries regarding the use or lack of the fragments keyword can be summarized as follows:
Be aware that you should not simply add the fragments keyword to every access list entry because the first fragment of the IP packet is considered a nonfragment and is treated independently of the subsequent fragments. An initial fragment will not match an access list permit or deny entry that contains the fragments keyword, the packet is compared to the next access list entry, and so on, until it is either permitted or denied by an access list entry that does not contain the fragments keyword. Therefore, you may need two access list entries for every deny entry. The first deny entry of the pair will not include the fragments keyword, and applies to the initial fragment. The second deny entry of the pair will include the fragments keyword and applies to the subsequent fragments. In the cases where there are multiple deny access list entries for the same host but with different Layer 4 ports, a single deny access-list entry with the fragments keyword for that host is all that needs to be added. Thus all the fragments of a packet are handled in the same manner by the access list.
Packet fragments of IP datagrams are considered individual packets and each counts individually as a packet in access list accounting and access list violation counts.
Note
Fragments and Policy Routing
Fragmentation and the fragment control feature affect policy routing if the policy routing is based on the match ip address command and the access list had entries that match on Layer 4 through 7 information. It is possible that noninitial fragments pass the access list and are policy routed, even if the first fragment was not policy routed or the reverse.
By using the fragments keyword in access list entries as described earlier, a better match between the action taken for initial and noninitial fragments can be made and it is more likely policy routing will occur as intended.
Examples
The following example sets a deny condition for a standard access list named Internetfilter:
ip access-list standard Internetfilterdeny 192.5.34.0 0.0.0.255permit 128.88.0.0 0.0.255.255permit 36.0.0.0 0.255.255.255! (Note: all other access implicitly denied)The following example denies HTTP traffic on Monday through Friday between the hours of 8:00 am and 6:00 p.m.:
time-range no-httpperiodic weekdays 8:00 to 18:00!ip access-list extended strictdeny tcp any any eq http time-range no-http!interface ethernet 0ip access-group strict inRelated Commands
dynamic
To define a named, dynamic, IP access list, use the dynamic access-list configuration command. To remove the access lists, use the no form of this command.
dynamic dynamic-name [timeout minutes] {deny | permit} protocol source source-wildcard destination destination-wildcard [precedence precedence] [tos tos] [log] [fragments]
no dynamic dynamic-name
Internet Control Message Protocol (ICMP)
For ICMP, you can also use the following syntax:
dynamic dynamic-name [timeout minutes] {deny | permit} icmp source source-wildcard destination destination-wildcard [icmp-type [icmp-code] | icmp-message] [precedence precedence] [tos tos] [log] [fragments]
Internet Group Management Protocol (IGMP)
For IGMP, you can also use the following syntax:
dynamic dynamic-name [timeout minutes] {deny | permit} igmp source source-wildcard destination destination-wildcard [igmp-type] [precedence precedence] [tos tos] [log] [fragments]
Transmission Control Protocol (TCP)
For TCP, you can also use the following syntax:
dynamic dynamic-name [timeout minutes] {deny | permit} tcp source source-wildcard [operator [port]] destination destination-wildcard [operator [port]] [established] [precedence precedence] [tos tos] [log] [fragments]
User Datagram Protocol (UDP)
For UDP, you can also use the following syntax:
dynamic dynamic-name [timeout minutes] {deny | permit} udp source source-wildcard [operator [port]] destination destination-wildcard [operator [port]] [precedence precedence] [tos tos] [log] [fragments]
Caution
Syntax Description
dynamic-name
Identifies this access list as a dynamic access list. Refer to lock-and-key access documented in the "Configuring Lock-and-Key Security (Dynamic Access Lists)" chapter in the Cisco IOS Security Configuration Guide.
timeout minutes
(Optional) Specifies the absolute length of time (in minutes) that a temporary access list entry can remain in a dynamic access list. The default is an infinite length of time and allows an entry to remain permanently. Refer to lock-and-key access documented in the "Configuring Lock-and-Key Security (Dynamic Access Lists)" chapter in the Cisco IOS Security Configuration Guide.
deny
Denies access if the conditions are matched.
permit
Permits access if the conditions are matched.
protocol
Name or number of an IP protocol. It can be one of the keywords eigrp, gre, icmp, igmp, igrp, ip, ipinip, nos, ospf, tcp, or udp, or an integer in the range 0 to 255 representing an IP protocol number. To match any Internet protocol (including ICMP, TCP, and UDP), use the keyword ip. Some protocols allow further qualifiers described later.
source
Number of the network or host from which the packet is being sent. There are three alternative ways to specify the source:
Use a 32-bit quantity in four-part, dotted-decimal format.
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Wildcard bits to be applied to source. There are three alternative ways to specify the source wildcard:
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destination
Number of the network or host to which the packet is being sent. There are three alternative ways to specify the destination:
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destination-wildcard
Wildcard bits to be applied to the destination. There are three alternative ways to specify the destination wildcard:
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precedence precedence
(Optional) Packets can be filtered by precedence level, as specified by a number from 0 to 7 or by name as listed in the section "Usage Guidelines."
tos tos
(Optional) Packets can be filtered by type of service level, as specified by a number from 0 to 15 or by name as listed in the section "Usage Guidelines."
log
(Optional) Causes an informational logging message about the packet that matches the entry to be sent to the console. (The level of messages logged to the console is controlled by the logging console command.)
The message includes the access list number, whether the packet was permitted or denied; the protocol, whether it was TCP, UDP, ICMP or a number; and, if appropriate, the source and destination addresses and source and destination port numbers. The message is generated for the first packet that matches, and then at 5-minute intervals, including the number of packets permitted or denied in the prior 5-minute interval.
Use the ip access-list log-update command to generate logging messages when the number of matches reaches a configurable threshold (rather than waiting for a 5-minute interval). See the ip access-list log-update command for more information.
The logging facility might drop some logging message packets if there are too many to be handled or if there is more than one logging message to be handled in 1 second. This behavior prevents the router from crashing due to too many logging packets. Therefore, the logging facility should not be used as a billing tool or an accurate source of the number of matches to an access list.
icmp-type
(Optional) ICMP packets can be filtered by ICMP message type. The type is a number from 0 to 255.
icmp-code
(Optional) ICMP packets that are filtered by ICMP message type can also be filtered by the ICMP message code. The code is a number from 0 to 255.
icmp-message
(Optional) ICMP packets can be filtered by an ICMP message type name or ICMP message type and code name. The possible names are found in the section "Usage Guidelines."
igmp-type
(Optional) IGMP packets can be filtered by IGMP message type or message name. A message type is a number from 0 to 15. IGMP message names are listed in the section "Usage Guidelines."
operator
(Optional) Compares source or destination ports. Possible operands include lt (less than), gt (greater than), eq (equal), neq (not equal), and range (inclusive range).
If the operator is positioned after the source and source-wildcard, it must match the source port.
If the operator is positioned after the destination and destination-wildcard, it must match the destination port.
The range operator requires two port numbers. All other operators require one port number.
port
(Optional) The decimal number or name of a TCP or UDP port. A port number is a number from 0 to 65535. TCP and UDP port names are listed in the "Usage Guidelines" section of the access-list (IP extended) command. TCP port names can only be used when filtering TCP. UDP port names can only be used when filtering UDP.
established
(Optional) For the TCP protocol only: Indicates an established connection. A match occurs if the TCP datagram has the ACK or RST bits set. The nonmatching case is that of the initial TCP datagram to form a connection.
fragments
(Optional) The access list entry applies to noninitial fragments of packets; the fragment is either permitted or denied accordingly. For more details about the fragments keyword, see the "Access List Processing of Fragments" and "Fragments and Policy Routing" sections in the "Usage Guidelines" section.
Defaults
An extended access list defaults to a list that denies everything. An extended access list is terminated by an implicit deny statement.
Command Modes
Access-list configuration
Command History
Usage Guidelines
You can use named access lists to control the transmission of packets on an interface and restrict contents of routing updates. The Cisco IOS software stops checking the extended access list after a match occurs.
Note
The following is a list of precedence names:
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The following is a list of ICMP message type names and ICMP message type and code names:
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The following is a list of IGMP message names:
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The following is a list of TCP port names that can be used instead of port numbers. Refer to the current Assigned Numbers RFC to find a reference to these protocols. Port numbers corresponding to these protocols can also be found by typing a ? in the place of a port number.
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The following is a list of UDP port names that can be used instead of port numbers. Refer to the current Assigned Numbers RFC to find a reference to these protocols. Port numbers corresponding to these protocols can also be found by typing a ? in the place of a port number.
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Access List Processing of Fragments
The behavior of access-list entries regarding the use or lack of the fragments keyword can be summarized as follows:
Be aware that you should not simply add the fragments keyword to every access list entry because the first fragment of the IP packet is considered a nonfragment and is treated independently of the subsequent fragments. An initial fragment will not match an access list permit or deny entry that contains the fragments keyword, the packet is compared to the next access list entry, and so on, until it is either permitted or denied by an access list entry that does not contain the fragments keyword. Therefore, you may need two access list entries for every deny entry. The first deny entry of the pair will not include the fragments keyword, and applies to the initial fragment. The second deny entry of the pair will include the fragments keyword and applies to the subsequent fragments. In the cases where there are multiple deny access list entries for the same host but with different Layer 4 ports, a single deny access-list entry with the fragments keyword for that host is all that needs to be added. Thus all the fragments of a packet are handled in the same manner by the access list.
Packet fragments of IP datagrams are considered individual packets and each counts individually as a packet in access list accounting and access list violation counts.
Note
Fragments and Policy Routing
Fragmentation and the fragment control feature affect policy routing if the policy routing is based on the match ip address command and the access list had entries that match on Layer 4 through 7 information. It is possible that noninitial fragments pass the access list and are policy routed, even if the first fragment was not policy routed or the reverse.
By using the fragments keyword in access list entries as described earlier, a better match between the action taken for initial and noninitial fragments can be made and it is more likely policy routing will occur as intended.
Examples
The following example defines a dynamic access list named washington:
ip access-group washington in!ip access-list extended washingtondynamic testlist timeout 5permit ip any anypermit tcp any host 185.302.21.2 eq 23Related Commands
forwarding-agent
To specify the port on which the forwarding agent will listen for wildcard and fixed affinities, use the forwarding-agent CASA-port configuration command. Use the no form of the command to disable listening on that port.
forwarding-agent number [password [timeout]]
no forwarding-agent
Syntax Description
Defaults
The default password timeout is 180 seconds.
The default port for the services manager is 1637.
Command Modes
CASA-port configuration
Command History
Examples
The following example specifies that the forwarding agent will listen for wildcard and fixed affinities on port 1637:
forwarding-agent 1637Related Commands
ip access-group
To control access to an interface, use the ip access-group interface configuration command. To remove the specified access group, use the no form of this command.
ip access-group {access-list-number | name}{in | out}
no ip access-group {access-list-number | name}{in | out}
Syntax Description
Defaults
No access list is applied to the interface.
Command Modes
Interface configuration
Command History
Usage Guidelines
Access lists are applied on either outbound or inbound interfaces. For standard inbound access lists, after receiving a packet, the Cisco IOS software checks the source address of the packet against the access list. For extended access lists, the router also checks the destination access list. If the access list permits the address, the software continues to process the packet. If the access list rejects the address, the software discards the packet and returns an ICMP Host Unreachable message.
For standard outbound access lists, after receiving and routing a packet to a controlled interface, the software checks the source address of the packet against the access list. For extended access lists, the router also checks the destination access list. If the access list permits the address, the software sends the packet. If the access list rejects the address, the software discards the packet and returns an ICMP Host Unreachable message.
If the specified access list does not exist, all packets are passed.
When you enable outbound access lists, you automatically disable autonomous switching for that interface.When you enable input access lists on any cBus or CxBus interface, you automatically disable autonomous switching for all interfaces (with one exception—an SSE configured with simple access lists can still switch packets, on output only).
Examples
The following example applies list 101 on packets outbound from Ethernet interface 0:
interface ethernet 0ip access-group 101 outRelated Commands
Defines an extended IP access list.
Defines a standard IP access list.
Defines an IP access list by name.
Displays the contents of current IP and rate-limit access lists.
ip access-list
To define an IP access list by name, use the ip access-list global configuration command. To remove a named IP access lists, use the no form of this command.
ip access-list {standard | extended} name
no ip access-list {standard | extended} name
Caution
Syntax Description
Defaults
No named IP access list is defined.
Command Modes
Global configuration
Command History
Usage Guidelines
Use this command to configure a named IP access list as opposed to a numbered IP access list. This command will take you into access-list configuration mode, where you must define the denied or permitted access conditions with the deny and permit commands.
Specifying the standard or extended keyword with the ip access-list command determines the prompt you get when you enter access-list configuration mode.
Use the ip access-group command to apply the access-list to an interface.
Named access lists are not compatible with Cisco IOS releases prior to Release 11.2.
Examples
The following example defines a standard access list named Internetfilter:
ip access-list standard Internetfilterpermit 192.5.34.0 0.0.0.255permit 128.88.0.0 0.0.255.255permit 36.0.0.0 0.255.255.255! (Note: all other access implicitly denied)Related Commands
Sets conditions for a named IP access list.
Controls access to an interface.
Sets conditions for a named IP access list.
Displays the contents of all current IP access lists.
ip access-list log-update
To set the threshold number of packets that generate a log message if they match an access list, use the ip access-list log-update command in global configuration mode. To remove the threshold, use the no form of this command.
ip access-list log-update threshold number-of-matches
no ip access-list log-update
Syntax Description
number-of-matches
Threshold number of packets necessary to match an access list before a log message is generated. The range is 0 to 2147483647. There is no default number of matches.
Defaults
Log messages are sent at the first matching packet and at 5-minute intervals after that.
Command Modes
Global configuration
Command History
Usage Guidelines
Log messages are generated if you have specified the log keyword in the access-list (IP standard), access-list (IP extended), deny (IP), dynamic, or permit command.
Log messages provide information about the packets that are permitted or denied by an access list. By default, log messages appear at the console. (The level of messages logged to the console is controlled by the logging console command.) The log message includes the access list number, whether the packet was permitted or denied, and other information.
By default, the log messages are sent at the first matching packet and after that, identical messages are accumulated for 5-minute intervals, with a single message being sent with the number of packets permitted and denied during that interval. However, you can use the ip access-list log-update command to set the number of packets that, when match an access list (and are permitted or denied), cause the system to generate a log message. You might want to do this to receive log messages more frequently than at 5-minute intervals.
Caution
Even if you use the ip access-list log-update command, the 5-minute timer remains in effect, so the cache is emptied at the end of 5 minutes, regardless of the count of messages in the cache. Regardless of when the log message is sent, the cache is flushed and the count reset to 0 for that message the same way it is when a threshold is not specified.
If the syslog server is not directly connected to a LAN that the router shares, any intermediate router might drop the log messages because they are UDP (unreliable) messages.
Examples
The following example enables logging whenever the 1000th packet matches an access list entry:
ip access-list log-update threshold 1000Related Commands
ip accounting
To enable IP accounting on an interface, use the ip accounting interface configuration command. To disable IP accounting, use the no form of this command.
ip accounting [access-violations] [output-packets]
no ip accounting [access-violations] [output-packets]
Syntax Description
Defaults
Disabled
Command Modes
Interface configuration
Command History
10.0
This command was introduced.
10.3
The access-violations keyword was added.
Usage Guidelines
The IP accounting command records the number of bytes (IP header and data) and packets switched through the system on a source and destination IP address basis. Only transit IP traffic is measured and only on an outbound basis; traffic generated by the router access server or terminating in this device is not included in the accounting statistics. Traffic coming from a remote site and transiting through a router is also recorded.
If you specify the access-violations keyword, the ip accounting command provides information identifying IP traffic that fails IP access lists. Identifying IP source addresses that violate IP access lists alerts you to possible attempts to breach security. The data might also indicate that you should verify IP access list configurations.
To receive a logging message on the console when an extended access list entry denies a packet access (to log violations), you must include the log keyword in the access-list (IP extended) or access-list (IP standard) command.
Statistics are accurate even if IP fast switching or IP access lists are being used on the interface.
IP accounting disables autonomous switching, SSE switching, and distributed switching (dCEF) on the interface. IP accounting will cause packets to be switched on the Route Switch Processor (RSP) instead of the Versatile Interface Processor (VIP), which can cause performance degradation.
Examples
The following example enables IP accounting on Ethernet interface 0:
interface ethernet 0ip accountingRelated Commands
ip accounting-list
To define filters to control the hosts for which IP accounting information is kept, use the ip accounting-list global configuration command. To remove a filter definition, use the no form of this command.
ip accounting-list ip-address wildcard
no ip accounting-list ip-address wildcard
Syntax Description
ip-address
IP address in dotted-decimal format.
wildcard
Wildcard bits to be applied to the ip-address argument.
Defaults
No filters are defined.
Command Modes
Global configuration
Command History
Usage Guidelines
The wildcard argument is a 32-bit quantity written in dotted-decimal format. Address bits corresponding to wildcard bits set to 1 are ignored in comparisons; address bits corresponding to wildcard bits set to zero are used in comparisons.
Examples
The following example adds all hosts with IP addresses beginning with 192.31 to the list of hosts for which accounting information will be kept:
ip accounting-list 192.31.0.0 0.0.255.255Related Commands
ip accounting-threshold
To set the maximum number of accounting entries to be created, use the ip accounting-threshold global configuration command. To restore the default number of entries, use the no form of this command.
ip accounting-threshold threshold
no ip accounting-threshold threshold
Syntax Description
threshold
Maximum number of entries (source and destination address pairs) that the Cisco IOS software accumulates.
Defaults
The default maximum number of accounting entries is 512 entries.
Command Modes
Global configuration
Command History
Usage Guidelines
The accounting threshold defines the maximum number of entries (source and destination address pairs) that the software accumulates, preventing IP accounting from possibly consuming all available free memory. This level of memory consumption could occur in a router that is switching traffic for many hosts. Overflows will be recorded; see the monitoring commands for display formats.
The default accounting threshold of 512 entries results in a maximum table size of 12,928 bytes. Active and checkpointed tables can reach this size independently.
Examples
The following example sets the IP accounting threshold to only 500 entries:
ip accounting-threshold 500Related Commands
ip accounting-transits
To control the number of transit records that are stored in the IP accounting database, use the ip accounting-transits global configuration command. To return to the default number of records, use the no form of this command.
ip accounting-transits count
no ip accounting-transits
Syntax Description
Defaults
The default number of transit records that are stored in the IP accounting database is 0.
Command Modes
Global configuration
Command History
Usage Guidelines
Transit entries are those that do not match any of the filters specified by ip accounting-list global configuration commands. If no filters are defined, no transit entries are possible.
To maintain accurate accounting totals, the Cisco IOS software maintains two accounting databases: an active and a checkpointed database.
Examples
The following example specifies that no more than 100 transit records are stored:
ip accounting-transits 100Related Commands
ip accounting mac-address
To enable IP accounting on a LAN interface based on the source and destination MAC address, use the ip accounting mac-address interface configuration command. To disable IP accounting based on the source and destination MAC address, use the no form of this command.
ip accounting mac-address {input | output]
no ip accounting mac-address {input | output]
Syntax Description
input
Performs accounting based on the source MAC address on received packets.
output
Performs accounting based on the destination MAC address on transmitted packets.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
This feature is supported on Ethernet, FastEthernet, and FDDI interfaces.
To display the MAC accounting information, use the show interface mac EXEC command.
MAC address accounting provides accounting information for IP traffic based on the source and destination MAC address on LAN interfaces. This calculates the total packet and byte counts for a LAN interface that receives or sends IP packets to or from a unique MAC address. It also records a timestamp for the last packet received or sent. With MAC address accounting, you can determine how much traffic is being sent to and/or received from various peers at NAPS/peering points.
Examples
The following example enables IP accounting based on the source and destination MAC address for received and transmitted packets:
interface ethernet 4/0/0ip accounting mac-address inputip accounting mac-address outputRelated Commands
Displays MAC accounting information for interfaces configured for MAC accounting.
ip accounting precedence
To enable IP accounting on any interface based on IP precedence, use the ip accounting precedence interface configuration command. To disable IP accounting based on IP precedence, use the no form of this command.
ip accounting precedence {input | output]
no ip accounting precedence {input | output]
Syntax Description
input
Performs accounting based on IP precedence on received packets.
output
Performs accounting based on IP precedence on transmitted packets.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
To display IP precedence accounting information, use the show interface precedence EXEC command.
The precedence accounting feature provides accounting information for IP traffic, summarized by IP precedence value(s). This feature calculates the total packet and byte counts for an interface that receives or sends IP packets and sorts the results based on IP precedence. This feature is supported on all interfaces and subinterfaces and supports CEF, dCEF, flow, and optimum switching.
Examples
The following example enables IP accounting based on IP precedence for received and transmitted packets:
interface ethernet 4/0/0ip accounting precedence inputip accounting precedence outputRelated Commands
Displays precedence accounting information for an interface configured for precedence accounting.
ip casa
To configure the router to function as a forwarding agent, use the ip casa global configuration command. Use the no form of the command to disable the forwarding agent.
ip casa control-address igmp-address
no ip casa
Syntax Description
Defaults
No default behavior or values.
Command Modes
Global configuration
Command History
Examples
The following example specifies the internet address (10.10.4.1) and IGMP address (224.0.1.2) for the forwarding agent:
ip-casa 10.10.4.1 224.0.1.2Related Commands
Specifies the port on which the forwarding agent will listen for wildcard and fixed affinities.
ip drp access-group
To control the sources of Director Response Protocol (DRP) queries to the DRP Server Agent, use the ip drp access-group global configuration command. To remove the access list, use the no form of this command.
ip drp access-group access-list-number
no ip drp access-group access-list-number
Syntax Description
Defaults
The DRP Server Agent will answer all queries.
Command Modes
Global configuration
Command History
Usage Guidelines
This command applies an access list to the interface, thereby controlling who can send queries to the DRP Server Agent.
If both an authentication key chain and an access group have been specified, both security measures must permit access before a request is processed.
Examples
The following example configures access list 1, which permits only queries from the host at 33.45.12.4:
access-list 1 permit 33.45.12.4ip drp access-group 1Related Commands
Configures authentication on the DRP Server Agent for DistributedDirector.
Displays information about the DRP Server Agent for DistributedDirector.
ip drp authentication key-chain
To configure authentication on the Director Response Protocol (DRP) Server Agent for Distributed Director, use the ip drp authentication key-chain global configuration command. To remove the key chain, use the no form of this command.
ip drp authentication key-chain name-of-chain
no ip drp authentication key-chain name-of-chain
Syntax Description
Defaults
No authentication is configured for the DRP Server Agent.
Command Modes
Global configuration
Command History
Usage Guidelines
When a key chain and key are configured, the key is used to authenticate all DRP requests and responses. The active key on the DRP Server Agent must match the active key on the primary agent. Use the key and key-string commands to configure the key.
Examples
The following example configures a key chain named ddchain:
ip drp authentication key-chain ddchainRelated Commands
ip drp server
To enable the Director Response Protocol (DRP) Server Agent that works with DistributedDirector, use the ip drp server global configuration command. To disable the DRP Server Agent, use the no form of this command.
ip drp server
no ip drp server
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Global configuration
Command History
Examples
The following example enables the DRP Server Agent:
ip drp serverRelated Commands
ip icmp rate-limit unreachable
To have the Cisco IOS software limit the rate that Internet Control Message Protocol (ICMP) destination unreachable messages are generated, use the ip icmp rate-limit unreachable global configuration command. To remove the rate limit, use the no form of this command.
ip icmp rate-limit unreachable [df] milliseconds
no ip icmp rate-limit unreachable [df]
Syntax Description
Defaults
The default value is one ICMP destination unreachable message per 500 milliseconds.
Command Modes
Global configuration
Command History
Usage Guidelines
The no ip icmp rate-limit unreachable command turns off the previously configured rate limit. To re-set the rate limit to its default value, use the default ip icmp rate-limit unreachable command.
The Cisco IOS software maintains two timers: one for general destination unreachable messages and one for DF destination unreachable messages. Both share the same time limits and defaults. If the df option is not configured, the ip icmp rate-limit unreachable command sets the time values for DF destination unreachable messages. If the df option is configured, its time values remain independent from those of general destination unreachable messages.
Examples
The following example sets the rate of the ICMP destination unreachable message to one message every 10 milliseconds:
ip icmp rate-limit unreachable 10The following example turns off the previously configured rate limit:
no ip icmp rate-limit unreachableThe following example sets the rate limit back to the default:
default ip icmp rate-limit unreachableip icmp redirect
To control the type of Internet Control Message Protocol (ICMP) redirect message that is sent by the Cisco IOS software, use the ip icmp redirect command in global configuration mode. To set the value back to the default, use the no form of this command.
ip icmp redirect [host | subnet]
no ip icmp redirect [host | subnet]
Syntax Description
Defaults
The router will send ICMP subnet redirect messages.
Because the ip icmp redirect subnet command is the default, the command will not be displayed in the configuration.
Command Modes
Global configuration
Command History
Usage Guidelines
An ICMP redirect message can be generated by a router when a packet is received and transmitted on the same interface. In this situation, the router will forward the original packet and send a ICMP redirect message back to the sender of the original packet. This behavior allows the sender to bypass the router and forward future packets directly to the destination (or a router closer to the destination).
There are two types of ICMP redirect messages: redirect for a host address or redirect for an entire subnet.
The ip icmp redirect command determines the type of ICMP redirects sent by the system and is configured on a per system basis. Some hosts do not understand ICMP subnet redirects and need the router to send out ICMP host redirects. Use the ip icmp redirect host command to have the router send out ICMP host redirects. Use the ip icmp redirect subnet command to set the value back to the default, which is to send subnet redirects.
To prevent the router from sending ICMP redirects, use the no ip redirects interface configuration command.
Examples
The following example enables the router to send out ICMP host redirects:
ip icmp redirect hostsThe following example sets the value back to the default, which is subnet redirects:
ip icmp redirect subnetRelated Commands
ip mask-reply
To have the Cisco IOS software respond to Internet Control Message Protocol (ICMP) mask requests by sending ICMP Mask Reply messages, use the ip mask-reply interface configuration command. To disable this function, use the no form of this command.
ip mask-reply
no ip mask-reply
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Examples
The following example enables the sending of ICMP Mask Reply messages on Ethernet interface 0:
interface ethernet 0ip address 131.108.1.0 255.255.255.0ip mask-replyip mtu
To set the maximum transmission unit (MTU) size of IP packets sent on an interface, use the ip mtu interface configuration command. To restore the default MTU size, use the no form of this command.
ip mtu bytes
no ip mtu
Syntax Description
Defaults
Minimum is 128 bytes; maximum depends on interface medium.
Command Modes
Interface configuration
Command History
Usage Guidelines
If an IP packet exceeds the MTU set for the interface, the Cisco IOS software will fragment it.
All devices on a physical medium must have the same protocol MTU in order to operate.
Note
Examples
The following example sets the maximum IP packet size for the first serial interface to 300 bytes:
interface serial 0ip mtu 300Related Commands
ip redirects
To enable the sending of Internet Control Message Protocol (ICMP) Redirect messages if the Cisco IOS software is forced to resend a packet through the same interface on which it was received, use the ip redirects interface configuration command. To disable the sending of redirect messages, use the no form of this command.
ip redirects
no ip redirects
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled, unless Hot Standby Router Protocol is configured
Command Modes
Interface configuration
Command History
Usage Guidelines
If the Hot Standby Router Protocol is configured on an interface, ICMP Redirect messages are disabled by default for the interface.
Examples
The following example enables the sending of ICMP Redirect messages on Ethernet interface 0:
interface ethernet 0ip redirectsRelated Commands
ip source-route
To allow the Cisco IOS software to handle IP datagrams with source routing header options, use the ip source-route global configuration command. To have the software discard any IP datagram containing a source-route option, use the no form of this command.
ip source-route
no ip source-route
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Global configuration
Command History
Examples
The following example enables the handling of IP datagrams with source routing header options:
ip source-routeRelated Commands
ip tcp chunk-size
To alter the TCP maximum read size for Telnet or rlogin, use the ip tcp chunk-size global configuration command. To restore the default value, use the no form of this command.
ip tcp chunk-size characters
no ip tcp chunk-size
Syntax Description
Defaults
0, which Telnet and rlogin interpret as the largest possible 32-bit positive number.
Command Modes
Global configuration
Command History
Usage Guidelines
It is unlikely you will need to change the default value.
Examples
The following example sets the maximum TCP read size to 64000 bytes:
ip tcp chunk-size 64000ip tcp compression-connections
To specify the total number of TCP header compression connections that can exist on an interface, use the ip tcp compression-connections interface configuration command. To restore the default, use the no form of this command.
ip tcp compression-connections number
no ip tcp compression-connections number
Syntax Description
number
Number of TCP header compression connections the cache supports, in the range from 3 to 1000. The default is 32 connections (16 calls).
Defaults
The default number 32 connections.
Command Modes
Interface configuration
Command History
Usage Guidelines
You should configure one connection for each TCP connection through the specified interface.
Each connection sets up a compression cache entry, so you are in effect specifying the maximum number of cache entries and the size of the cache. Too few cache entries for the specified interface can lead to degraded performance, while too many cache entries can lead to wasted memory.
Note
Examples
The following example sets the first serial interface for header compression with a maximum of ten cache entries:
interface serial 0ip tcp header-compressionip tcp compression-connections 10Related Commands
ip rtp header-compression
Enables RTP header compression.
Enables TCP header compression.
show ip rtp header-compression
Displays RTP header compression statistics.
ip tcp header-compression
To enable TCP header compression, use the ip tcp header-compression interface configuration command. To disable compression, use the no form of this command.
ip tcp header-compression [passive]
no ip tcp header-compression [passive]
Syntax Description
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
You can compress the headers of your TCP/IP packets in order to reduce the size of your packets. TCP header compression is supported on serial lines using Frame Relay, HDLC or Point-to-Point (PPP) encapsulation. You must enable compression on both ends of a serial connection. RFC 1144 specifies the compression process. Compressing the TCP header can speed up Telnet connections dramatically. In general, TCP header compression is advantageous when your traffic consists of many small packets, not for traffic that consists of large packets. Transaction processing (usually using terminals) tends to use small packets while file transfers use large packets. This feature only compresses the TCP header, so it has no effect on UDP packets or other protocol headers.
When compression is enabled, fast switching is disabled. This means that fast interfaces like T1 can overload the router. Consider your network's traffic characteristics before using this command.
Examples
The following example sets the first serial interface for header compression with a maximum of ten cache entries:
interface serial 0ip tcp header-compressionip tcp compression-connections 10Related Commands
Specifies the total number of header compression connections that can exist on an interface.
ip tcp mss
To enable a maximum segment size (MSS) for TCP connections originating or terminating on a router, use the ip tcp mss command in global configuration mode. To disable the configuration of the MSS, use the no form of this command.
ip tcp mss mss-value
no ip tcp mss mss-value
Syntax Description
Defaults
This command is disabled.
Command Modes
Global configuration
Command History
12.0(05)S
This command was introduced.
12.1
This command was integrated into Cisco IOS Release 12.1.
Usage Guidelines
If this command is not enabled, the MSS value of 536 bytes is used if the destination is not on a LAN, otherwise the MSS value is 1460 for a local destination.
For connections originating from a router, the specified value is used directly as an MSS option in the synchronize (SYN) segment. For connections terminating on a router, the value is used only if the incoming SYN segment has an MSS option value higher than the configured value. Otherwise the incoming value is used as the MSS option in the SYN/acknowledge (ACK) segment.
Note
Examples
The following example sets the MSS value at 250:
ip tcp mss 250Related Commands
ip tcp header-compression
Specifies the total number of header compression connections that can exist on an interface.
ip tcp path-mtu-discovery
To enable Path MTU Discovery for all new TCP connections from the router, use the ip tcp path-mtu-discovery global configuration command. To disable the function, use the no form of this command.
ip tcp path-mtu-discovery [age-timer {minutes | infinite}]
no ip tcp path-mtu-discovery [age-timer {minutes | infinite}]
Syntax Description
Defaults
Disabled. If enabled, default minutes is 10 minutes.
Command Modes
Global configuration
Command History
10.3
This command was introduced.
11.2
The following keywords were added:
•
•
Usage Guidelines
Path MTU Discovery is a method for maximizing the use of available bandwidth in the network between the end points of a TCP connection. It is described in RFC 1191. Existing connections are not affected when this feature is turned on or off.
Customers using TCP connections to move bulk data between systems on distinct subnets would benefit most by enabling this feature. This might include customers using RSRB with TCP encapsulation, STUN, X.25 Remote Switching (also known as XOT, or X.25 over TCP), and some protocol translation configurations.
The age timer is a time interval for how often TCP re-estimates the Path MTU with a larger MSS. By using the age timer, TCP Path MTU becomes a dynamic process. If MSS used for the connection is smaller than what the peer connection can handle, a larger MSS is tried every time the age timer expires. The discovery process is stopped when either the send MSS is as large as the peer negotiated, or the user has disabled the timer on the router. You can turn off the age-timer by setting it to infinite.
Examples
The following example enables Path MTU Discovery:
ip tcp path-mtu-discoveryip tcp queuemax
To alter the maximum TCP outgoing queue per connection, use the ip tcp queuemax global configuration command. To restore the default value, use the no form of this command.
ip tcp queuemax packets
no ip tcp queuemax
Syntax Description
packets
Outgoing queue size of TCP packets. The default value is 5 segments if the connection has a TTY associated with it. If there is no TTY associated with it, the default value is 20 segments.
Defaults
The default value is 5 segments if the connection has a TTY associated with it. If there is no TTY associated with it, the default value is 20 segments.
Command Modes
Global configuration
Command History
Usage Guidelines
Changing the default value changes the 5 segments, not the 20 segments.
Examples
The following example sets the maximum TCP outgoing queue to 10 packets:
ip tcp queuemax 10ip tcp selective-ack
To enable TCP selective acknowledgment, use the ip tcp selective-ack global configuration command. To disable TCP selective acknowledgment, use the no form of this command.
ip tcp selective-ack
no ip tcp selective-ack
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
TCP might not experience optimal performance if multiple packets are lost from one window of data. With the limited information available from cumulative acknowledgments, a TCP sender can learn about only one lost packet per round trip time. An aggressive sender could re-send packets early, but such re-sent segments might have already been successfully received.
The TCP selective acknowledgment mechanism helps overcome these limitations. The receiving TCP returns selective acknowledgment packets to the sender, informing the sender about data that has been received. The sender can then re-send only the missing data segments.
TCP selective acknowledgment improves overall performance. The feature is used only when multiple packets drop from a TCP window. There is no performance impact when the feature is enabled but not used.
This command becomes effective only on new TCP connections opened after the feature is enabled.
This feature must be disabled if you want TCP header compression. You might disable this feature if you have severe TCP problems.
Refer to RFC 2018 for more detailed information on TCP selective acknowledgment.
Examples
The following example enables the router to send and receive TCP selective acknowledgments:
ip tcp selective-ackRelated Commands
ip tcp synwait-time
To set a period of time the Cisco IOS software waits while attempting to establish a TCP connection before it times out, use the ip tcp synwait-time global configuration command. To restore the default time, use the no form of this command.
ip tcp synwait-time seconds
no ip tcp synwait-time seconds
Syntax Description
seconds
Time in seconds the software waits while attempting to establish a TCP connection. It can be an integer from 5 to 300 seconds. The default is 30 seconds.
Defaults
The default time is 30 seconds.
Command Modes
Global configuration
Command History
Usage Guidelines
In versions previous to Cisco IOS software 10.0, the system would wait a fixed 30 seconds when attempting to establish a TCP connection. If your network contains Public Switched Telephone Network (PSTN) dial-on-demand routing (DDR), the call setup time may exceed 30 seconds. This amount of time is not sufficient in networks that have dial-up asynchronous connections because it will affect your ability to Telnet over the link (from the router) if the link must be brought up. If you have this type of network, you might want to set this value to the UNIX value of 75.
Because this is a host parameter, it does not pertain to traffic going through the router, just for traffic originated at this device. Because UNIX has a fixed 75-second timeout, hosts are unlikely to see this problem.
Examples
The following example configures the Cisco IOS software to continue attempting to establish a TCP connection for 180 seconds:
ip tcp synwait-time 180ip tcp timestamp
To enable TCP time stamp, use the ip tcp timestamp global configuration command. To disable TCP timestamp, use the no form of this command.
ip tcp timestamp
no ip tcp timestamp
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
TCP time stamp improves round-trip time estimates. Refer to RFC 1323 for more detailed information on TCP timestamp.
This feature must be disabled if you want to use TCP header compression.
Examples
The following example enables the router to send TCP timestamps:
ip tcp timestampRelated Commands
ip tcp window-size
To alter the TCP window size, use the ip tcp window-size global configuration command. To restore the default value, use the no form of this command.
ip tcp window-size bytes
no ip tcp window-size
Syntax Description
Defaults
The default size is 2144 bytes.
Command Modes
Global configuration
Command History
Usage Guidelines
Do not use this command unless you clearly understand why you want to change the default value.
If your TCP window size is set to 1000 bytes, for example, you could have 1 packet of 1000 bytes or 2 packets of 500 bytes, and so on. However, there is also a limit on the number of packets allowed in the window. There can be a maximum of 5 packets if the connection has TTY; otherwise there can be 20 packets.
Examples
The following example sets the TCP window size to 1000 bytes:
ip tcp window-size 1000ip unreachables
To enable the generation of Internet Control Message Protocol (ICMP) Unreachable messages, use the ip unreachables interface configuration command. To disable this function, use the no form of this command.
ip unreachables
no ip unreachables
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Interface configuration
Command History
Usage Guidelines
If the Cisco IOS software receives a nonbroadcast packet destined for itself that uses a protocol it does not recognize, it sends an ICMP Protocol Unreachable message to the source.
If the software receives a datagram that it cannot deliver to its ultimate destination because it knows of no route to the destination address, it replies to the originator of that datagram with an ICMP Host Unreachable message.
This command affects all kinds of ICMP unreachable messages.
Examples
The following example enables the generation of ICMP Unreachable messages, as appropriate, on an interface:
interface ethernet 0ip unreachablespermit (IP)
To set conditions for a named IP access list, use the permit access-list configuration command. To remove a condition from an access list, use the no form of this command.
permit source [source-wildcard]
no permit source [source-wildcard]
permit protocol source source-wildcard destination destination-wildcard [precedence precedence] [tos tos] [log] [time-range time-range-name] [fragments]
no permit protocol source source-wildcard destination destination-wildcard [precedence precedence] [tos tos] [log] [time-range time-range-name]
Internet Control Message Protocol (ICMP)
For ICMP, you can also use the following syntax:
permit icmp source source-wildcard destination destination-wildcard [icmp-type [icmp-code] | icmp-message] [precedence precedence] [tos tos] [log] [time-range time-range-name] [fragments]
Internet Group Management Protocol (IGMP)
For IGMP, you can also use the following syntax:
permit igmp source source-wildcard destination destination-wildcard [igmp-type] [precedence precedence] [tos tos] [log] [time-range time-range-name] [fragments]
Transmission Control Protocol (TCP)
For TCP, you can also use the following syntax:
permit tcp source source-wildcard [operator [port]] destination destination-wildcard [operator [port]] [established] [precedence precedence] [tos tos] [log] [time-range time-range-name] [fragments]
User Datagram Protocol (UDP)
For UDP, you can also use the following syntax:
permit udp source source-wildcard [operator [port]] destination destination-wildcard [operator [port]] [precedence precedence] [tos tos] [log] [time-range time-range-name] [fragments]
Syntax Description
source
Number of the network or host from which the packet is being sent. There are three alternative ways to specify the source:
•
•
•
source-wildcard
Wildcard bits to be applied to source. There are three alternative ways to specify the source wildcard:
•
•
•
protocol
Name or number of an IP protocol. It can be one of the keywords eigrp, gre, icmp, igmp, igrp, ip, ipinip, nos, ospf, tcp, or udp, or an integer in the range 0 to 255 representing an IP protocol number. To match any Internet protocol (including ICMP, TCP, and UDP), use the keyword ip. Some protocols allow further qualifiers described later.
destination
Number of the network or host to which the packet is being sent. There are three alternative ways to specify the destination:
•
•
•
destination-wildcard
Wildcard bits to be applied to the destination. There are three alternative ways to specify the destination wildcard:
•
•
•
precedence precedence
(Optional) Packets can be filtered by precedence level, as specified by a number from 0 to 7 or by name as listed in the section "Usage Guidelines."
tos tos
(Optional) Packets can be filtered by type of service level, as specified by a number from 0 to 15 or by name as listed in the "Usage Guidelines" section of the access-list (IP extended) command.
log
(Optional) Causes an informational logging message about the packet that matches the entry to be sent to the console. (The level of messages logged to the console is controlled by the logging console command.)
The message includes the access list number, whether the packet was permitted or denied; the protocol, whether it was TCP, UDP, ICMP or a number; and, if appropriate, the source and destination addresses and source and destination port numbers. The message is generated for the first packet that matches, and then at 5-minute intervals, including the number of packets permitted or denied in the prior 5-minute interval.
Use the ip access-list log-update command to generate logging messages when the number of matches reaches a configurable threshold (rather than waiting for a 5-minute interval). See the ip access-list log-update command for more information.
The logging facility might drop some logging message packets if there are too many to be handled or if there is more than one logging message to be handled in 1 second. This behavior prevents the router from crashing due to too many logging packets. Therefore, the logging facility should not be used as a billing tool or an accurate source of the number of matches to an access list.
If you enable CEF and then create an access list that uses the log keyword, the packets that match the access list are not CEF switched. They are fast switched. Logging disables CEF.
time-range time-range-name
(Optional) Name of the time range that applies to this permit statement. The name of the time range and its restrictions are specified by the time-range and absolute or periodic commands, respectively.
icmp-type
(Optional) ICMP packets can be filtered by ICMP message type. The type is a number from 0 to 255.
icmp-code
(Optional) ICMP packets which are filtered by ICMP message type can also be filtered by the ICMP message code. The code is a number from 0 to 255.
icmp-message
(Optional) ICMP packets can be filtered by an ICMP message type name or ICMP message type and code name. The possible names are found in the "Usage Guidelines" section of the access-list (IP extended) command.
igmp-type
(Optional) IGMP packets can be filtered by IGMP message type or message name. A message type is a number from 0 to 15. IGMP message names are listed in the "Usage Guidelines" section of the access-list (IP extended) command.
operator
(Optional) Compares source or destination ports. Possible operands include lt (less than), gt (greater than), eq (equal), neq (not equal), and range (inclusive range).
If the operator is positioned after the source and source-wildcard, it must match the source port.
If the operator is positioned after the destination and destination-wildcard, it must match the destination port.
The range operator requires two port numbers. All other operators require one port number.
port
(Optional) The decimal number or name of a TCP or UDP port. A port number is a number from 0 to 65535. TCP and UDP port names are listed in the "Usage Guidelines" section of the access-list (IP extended) command. TCP port names can only be used when filtering TCP. UDP port names can only be used when filtering UDP.
established
(Optional) For the TCP protocol only: Indicates an established connection. A match occurs if the TCP datagram has the ACK or RST bits set. The nonmatching case is that of the initial TCP datagram to form a connection.
fragments
(Optional) The access list entry applies to noninitial fragments of packets; the fragment is either permitted or denied accordingly. For more details about the fragments keyword, see the "Access List Processing of Fragments" and "Fragments and Policy Routing" sections in the "Usage Guidelines" section.
Defaults
There are no specific conditions under which a packet passes the named access list.
Command Modes
Access-list configuration
Command History
11.2
This command was introduced.
12.0(1)T
The time-range time-range-name keyword and argument were added.
12.1(2)
The fragments keyword was added.
Usage Guidelines
Use this command following the ip access-list command to define the conditions under which a packet passes the access list.
The time-range option allows you to identify a time range by name. The time-range, absolute, and periodic commands specify when this permit statement is in effect.
Access List Processing of Fragments
The behavior of access-list entries regarding the use or lack of the fragments keyword can be summarized as follows:
Be aware that you should not simply add the fragments keyword to every access list entry because the first fragment of the IP packet is considered a nonfragment and is treated independently of the subsequent fragments. An initial fragment will not match an access list permit or deny entry that contains the fragments keyword, the packet is compared to the next access list entry, and so on, until it is either permitted or denied by an access list entry that does not contain the fragments keyword. Therefore, you may need two access list entries for every deny entry. The first deny entry of the pair will not include the fragments keyword, and applies to the initial fragment. The second deny entry of the pair will include the fragments keyword and applies to the subsequent fragments. In the cases where there are multiple deny access list entries for the same host but with different Layer 4 ports, a single deny access-list entry with the fragments keyword for that host is all that needs to be added. Thus all the fragments of a packet are handled in the same manner by the access list.
Packet fragments of IP datagrams are considered individual packets and each counts individually as a packet in access list accounting and access list violation counts.
Note
Fragments and Policy Routing
Fragmentation and the fragment control feature affect policy routing if the policy routing is based on the match ip address command and the access list had entries that match on Layer 4 through 7 information. It is possible that noninitial fragments pass the access list and are policy routed, even if the first fragment was not policy routed or the reverse.
By using the fragments keyword in access list entries as described earlier, a better match between the action taken for initial and noninitial fragments can be made and it is more likely policy routing will occur as intended.
Examples
The following example sets conditions for a standard access list named Internetfilter:
ip access-list standard Internetfilterdeny 192.5.34.0 0.0.0.255permit 128.88.0.0 0.0.255.255permit 36.0.0.0 0.255.255.255! (Note: all other access implicitly denied)The following example permits Telnet traffic on Mondays, Tuesdays, and Fridays between the hours of 9:00 am and 5:00 pm:
time-range testingperiodic Monday Tuesday Friday 9:00 to 17:00!ip access-list extended legalpermit tcp any any eq telnet time-range testing!interface ethernet 0ip access-group legal inRelated Commands
remark
To write a helpful comment (remark) for an entry in a named IP access list, use the remark access-list configuration command. To remove the remark, use the no form of this command.
remark remark
no remark remark
Syntax Description
Defaults
The access list entries have no remarks.
Command Modes
Standard named or extended named access-list configuration
Command History
Usage Guidelines
The remark can be up to 100 characters; anything longer is truncated.
If you want to write a comment about an entry in a numbered IP access list, use the access-list remark command.
Examples
In the following example, the Jones subnet is not allowed to use outbound Telnet:
ip access-list extended telnettingremark Do not allow Jones subnet to telnet outdeny tcp host 171.69.2.88 any eq telnetRelated Commands
show access-lists
To display the contents of current access lists, use the show access-lists privileged EXEC command.
show access-lists [access-list-number | name]
Syntax Description
access-list-number
(Optional) Number of the access list to display. The system displays all access lists by default.
name
(Optional) Name of the IP access list to display.
Defaults
The system displays all access lists.
Command Modes
Privileged EXEC
Command History
Examples
The following is sample output from the show access-lists command when access list 101 is specified:
Router# show access-lists 101Extended IP access list 101permit tcp host 198.92.32.130 any established (4304 matches) check=5permit udp host 198.92.32.130 any eq domain (129 matches)permit icmp host 198.92.32.130 anypermit tcp host 198.92.32.130 host 171.69.2.141 gt 1023permit tcp host 198.92.32.130 host 171.69.2.135 eq smtp (2 matches)permit tcp host 198.92.32.130 host 198.92.30.32 eq smtppermit tcp host 198.92.32.130 host 171.69.108.33 eq smtppermit udp host 198.92.32.130 host 171.68.225.190 eq syslogpermit udp host 198.92.32.130 host 171.68.225.126 eq syslogdeny ip 150.136.0.0 0.0.255.255 224.0.0.0 15.255.255.255deny ip 171.68.0.0 0.1.255.255 224.0.0.0 15.255.255.255 (2 matches) check=1deny ip 172.24.24.0 0.0.1.255 224.0.0.0 15.255.255.255deny ip 192.82.152.0 0.0.0.255 224.0.0.0 15.255.255.255deny ip 192.122.173.0 0.0.0.255 224.0.0.0 15.255.255.255deny ip 192.122.174.0 0.0.0.255 224.0.0.0 15.255.255.255deny ip 192.135.239.0 0.0.0.255 224.0.0.0 15.255.255.255deny ip 192.135.240.0 0.0.7.255 224.0.0.0 15.255.255.255deny ip 192.135.248.0 0.0.3.255 224.0.0.0 15.255.255.255An access list counter counts how many packets are allowed by each line of the access list. This number is displayed as the number of matches. Check denotes how many times a packet was compared to the access list but did not match.
For information on how to configure access lists, refer to the "Configuring IP Services" chapter of the Cisco IOS IP and IP Routing Configuration Guide.
For information on how to configure dynamic access lists, refer to the "Traffic Filtering and Firewalls" chapter of the Cisco IOS Security Configuration Guide.
Related Commands
show interface mac
To display MAC accounting information for interfaces configured for MAC accounting, use the show interface mac EXEC command.
show interface [type number] mac
Syntax Description
Command Modes
EXEC
Command History
Usage Guidelines
The show interface mac command displays information for all interfaces configured for MAC accounting. To display information for a single interface, use the show interface type number mac command.
For incoming packets on the interface, the accounting statistics are gathered before the CAR/DCAR feature is performed on the packet. For outgoing packets on the interface, the accounting statistics are gathered after output CAR, before output DCAR or DWRED or DWFQ feature is performed on the packet. Therefore, if a you are using DCAR or DWRED on the interface and packets are dropped, the dropped packets are still counted in the show interface mac command because the calculations are done prior to the features.
The maximum number of MAC addresses that can be stored for the input address is 512 and the maximum number of MAC address that can be stored for the output address is 512. After the maximum is reached, subsequent MAC addresses are ignored.
To clear the accounting statistics, use the clear counter EXEC command.
To configure an interface for IP accounting based on the MAC address, use the ip accounting mac-address interface configuration command.
Examples
The following is sample output from the show interface mac command. This feature calculates the total packet and byte counts for the interface that receives (input) or sends (output) IP packets to or from a unique MAC address. It also records a timestamp for the last packet received or sent.
Router# show interface ethernet 0/1/1 macEthernet0/1/1Input (511 free)0007.f618.4449(228): 4 packets, 456 bytes, last: 2684ms agoTotal: 4 packets, 456 bytesOutput (511 free)0007.f618.4449(228): 4 packets, 456 bytes, last: 2692ms agoTotal: 4 packets, 456 bytesRelated Commands
Enables IP accounting on any interface based on the source and destination MAC address.
show interface precedence
To display precedence accounting information for interfaces configured for precedence accounting, use the show interface precedence EXEC command.
show interface [type number] precedence
Syntax Description
Command Modes
EXEC
Command History
Usage Guidelines
The show interface precedence command displays information for all interfaces configured for IP precedence accounting. To display information for a single interface, use the show interface type number precedence command.
For incoming packets on the interface, the accounting statistics are gathered before input CAR/DCAR is performed on the packet. Therefore, if CAR/DCAR changes the precedence on the packet, it is counted based on the old precedence setting with the show interface precedence command.
For outgoing packets on the interface, the accounting statistics are gathered after output DCAR or DWRED or DWFQ feature is performed on the packet.
To clear the accounting statistics, use the clear counter EXEC command.
To configure an interface for IP accounting based on IP precedence, use the ip accounting precedence interface configuration command.
Examples
The following is sample output from the show interface precedence command. This feature calculates the total packet and byte counts for the interface that receives (input) or sends (output) IP packets and sorts the results based on IP precedence.
Router# show interface ethernet 0/1/1 precedenceEthernet0/1/1InputPrecedence 0: 4 packets, 456 bytesOutputPrecedence 0: 4 packets, 456 bytesRelated Commands
show ip access-list
To display the contents of all current IP access lists, use the show ip access-list EXEC command.
show ip access-list [access-list-number | name]
Syntax Description
access-list-number
(Optional) Number of the IP access list to display.
name
(Optional) Name of the IP access list to display.
Defaults
Displays all standard and extended IP access lists.
Command Modes
EXEC
Command History
Usage Guidelines
The show ip access-list command provides output identical to the show access-lists command, except that it is IP-specific and allows you to specify a particular access list.
Examples
The following is sample output from the show ip access-list command when all are requested:
Router# show ip access-listExtended IP access list 101deny udp any any eq ntppermit tcp any anypermit udp any any eq tftppermit icmp any anypermit udp any any eq domainThe following is sample output from the show ip access-list command when the name of a specific access list is requested:
Router# show ip access-list InternetfilterExtended IP access list Internetfilterpermit tcp any 171.69.0.0 0.0.255.255 eq telnetdeny tcp any anydeny udp any 171.69.0.0 0.0.255.255 lt 1024deny ip any any logshow ip accounting
To display the active accounting or checkpointed database or to display access list violations, use the show ip accounting EXEC command.
show ip accounting [checkpoint] [output-packets | access-violations]
Syntax Description
Defaults
If neither the output-packets nor access-violations keyword is specified, show ip accounting displays information pertaining to packets that passed access control and were successfully routed.
Command Modes
EXEC
Command History
10.0
This command was introduced.
10.3
The following keywords were added:
•
•
Usage Guidelines
If you do not specify any keywords, the show ip accounting command displays information about the active accounting database.
To display IP access violations, you must give the access-violations keyword on the command. If you do not specify the keyword, the command defaults to displaying the number of packets that have passed access lists and were routed.
To use this command, you must first enable IP accounting on a per-interface basis.
Examples
The following is sample output from the show ip accounting command:
Router# show ip accountingSource Destination Packets Bytes131.108.19.40 192.67.67.20 7 306131.108.13.55 192.67.67.20 67 2749131.108.2.50 192.12.33.51 17 1111131.108.2.50 130.93.2.1 5 319131.108.2.50 130.93.1.2 463 30991131.108.19.40 130.93.2.1 4 262131.108.19.40 130.93.1.2 28 2552131.108.20.2 128.18.6.100 39 2184131.108.13.55 130.93.1.2 35 3020131.108.19.40 192.12.33.51 1986 95091131.108.2.50 192.67.67.20 233 14908131.108.13.28 192.67.67.53 390 24817131.108.13.55 192.12.33.51 214669 9806659131.108.13.111 128.18.6.23 27739 1126607131.108.13.44 192.12.33.51 35412 1523980192.31.7.21 130.93.1.2 11 824131.108.13.28 192.12.33.2 21 1762131.108.2.166 192.31.7.130 797 141054131.108.3.11 192.67.67.53 4 246192.31.7.21 192.12.33.51 15696 695635192.31.7.24 192.67.67.20 21 916131.108.13.111 128.18.10.1 16 1137accounting threshold exceeded for 7 packets and 433 bytesThe following is sample output from the show ip accounting access-violations command. The output pertains to packets that failed access lists and were not routed:
Router# show ip accounting access-violationsSource Destination Packets Bytes ACL131.108.19.40 192.67.67.20 7 306 77131.108.13.55 192.67.67.20 67 2749 185131.108.2.50 192.12.33.51 17 1111 140131.108.2.50 130.93.2.1 5 319 140131.108.19.40 130.93.2.1 4 262 77Accounting data age is 41The following is sample output from the show ip accounting command. The output shows the original source and destination addresses that are separated by three routers:
Router3# show ip accountingSource Destination Packets Bytes10.225.231.154 172.16.10.2 44 2816010.76.97.34 172.16.10.2 44 2816010.10.11.1 172.16.10.2 507 32448010.10.10.1 172.16.10.2 507 31839610.100.45.1 172.16.10.2 508 32512010.98.32.5 172.16.10.2 44 28160Accounting data age is 2Table 15 describes the fields shown in the displays.
Related Commands
show ip casa affinities
To display statistics about affinities, use the show ip casa affinities EXEC command.
show ip casa affinities [stats] | [saddr ipaddr [detail]] | [daddr ipaddr [detail]] | sport sport [detail]] | dport dport [detail]] | protocol protocol [detail]]
Syntax Description
Command Modes
EXEC
Command History
Examples
The following is sample output of the show ip casa affinities command:
Router# show ip casa affinitiesAffinity TableSource Address Port Dest Address Port Prot161.44.36.118 1118 172.26.56.13 19 TCP172.26.56.13 19 161.44.36.118 1118 TCPThe following is sample output of the show ip casa affinities detail command:
Router# show ip casa affinities detailAffinity TableSource Address Port Dest Address Port Prot161.44.36.118 1118 172.26.56.13 19 TCPAction Details:Interest Addr: 172.26.56.19 Interest Port: 1638Interest Packet: 0x0102 SYN FRAGInterest Tickle: 0x0005 FIN RSTDispatch (Layer 2): YES Dispatch Address: 172.26.56.33Source Address Port Dest Address Port Prot172.26.56.13 19 161.44.36.118 1118 TCPAction Details:Interest Addr: 172.26.56.19 Interest Port: 1638Interest Packet: 0x0104 RST FRAGInterest Tickle: 0x0003 FIN SYNDispatch (Layer 2): NO Dispatch Address: 0.0.0.0Table 16 describes significant fields shown in the display.
Related Commands
Specifies the port on which the forwarding agent will listen for wildcard and fixed affinities.
Displays operational information about the forwarding agent.
show ip casa oper
To display operational information about the forwarding agent, use the show ip casa oper EXEC command.
show ip casa oper
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following is sample output of the show ip casa oper command:
Router# show ip casa operCasa is ActiveCasa control address is 206.10.20.34/32Casa multicast address is 224.0.1.2Listening for wildcards on:Port:1637Current passwd:NONE Pending passwd:NONEPasswd timeout:180 sec (Default)Table 17 describes significant fields shown in the display.
Related Commands
show ip casa stats
To display statistical information about the forwarding agent, use the show ip casa stats EXEC command.
show ip casa stats
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following is sample output of the show ip casa stats command:
Router# show ip casa statsCasa is active:Wildcard Stats:Wildcards: 6 Max Wildcards: 6Wildcard Denies: 0 Wildcard Drops: 0Pkts Throughput: 441 Bytes Throughput: 39120Affinity Stats:Affinities: 2 Max Affinities: 2Cache Hits: 444 Cache Misses: 0Affinity Drops: 0Casa Stats:Int Packet: 4 Int Tickle: 0Casa Denies: 0 Drop Count: 0Table 18 describes significant fields shown in the display.
.
Related Commands
show ip casa wildcard
To display information about wildcard blocks, use the show ip casa wildcard EXEC command.
show ip casa wildcard [detail]
Syntax Description
Command Modes
EXEC
Command History
Examples
The following is sample output of the show ip casa wildcard command:
Router# show ip casa wildcardSource Address Source Mask Port Dest Address Dest Mask Port Prot0.0.0.0 0.0.0.0 0 172.26.56.2 255.255.255.255 0 ICMP0.0.0.0 0.0.0.0 0 172.26.56.2 255.255.255.255 0 TCP0.0.0.0 0.0.0.0 0 172.26.56.13 255.255.255.255 0 ICMP0.0.0.0 0.0.0.0 0 172.26.56.13 255.255.255.255 0 TCP172.26.56.2 255.255.255.255 0 0.0.0.0 0.0.0.0 0 TCP172.26.56.13 255.255.255.255 0 0.0.0.0 0.0.0.0 0 TCPThe following is sample output of the show ip casa wildcard detail command:
router# show ip casa wildcard detailSource Address Source Mask Port Dest Address Dest Mask Port Prot0.0.0.0 0.0.0.0 0 172.26.56.2 255.255.255.255 0 ICMPService Manager Details:Manager Addr: 172.26.56.19 Insert Time: 08:21:27 UTC 04/18/96Affinity Statistics:Affinity Count: 0 Interest Packet Timeouts: 0Packet Statistics:Packets: 0 Bytes: 0Action Details:Interest Addr: 172.26.56.19 Interest Port: 1638Interest Packet: 0x8000 ALLPKTSInterest Tickle: 0x0107 FIN SYN RST FRAGDispatch (Layer 2): NO Dispatch Address: 0.0.0.0Advertise Dest Address: YES Match Fragments: NOSource Address Source Mask Port Dest Address Dest Mask Port Prot0.0.0.0 0.0.0.0 0 172.26.56.2 255.255.255.255 0 TCPService Manager Details:Manager Addr: 172.26.56.19 Insert Time: 08:21:27 UTC 04/18/96Affinity Statistics:Affinity Count: 0 Interest Packet Timeouts: 0Packet Statistics:Packets: 0 Bytes: 0Action Details:Interest Addr: 172.26.56.19 Interest Port: 1638Interest Packet: 0x8102 SYN FRAG ALLPKTSInterest Tickle: 0x0005 FIN RSTDispatch (Layer 2): NO Dispatch Address: 0.0.0.0Advertise Dest Address: YES Match Fragments: NO
Note
Table 19 describes significant fields shown in the display.
Related Commands
show ip drp
To display information about the Director Response Protocol (DRP) Server Agent for DistributedDirector, use the show ip drp EXEC command.
show ip drp
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following is sample output from the show ip drp command:
Router# show ip drpDirector Responder Protocol Agent is enabled717 director requests, 712 successful lookups, 5 failures, 0 no routeAuthentication is enabled, using "test" key-chainTable 20 describes the significant fields in the display.
Related Commands
Controls the sources of DRP queries to the DRP Server Agent.
Configures authentication on the DRP Server Agent for DistributedDirector.
show ip redirects
To display the address of a default gateway (router) and the address of hosts for which an Internet Control Message Protocol (ICMP) Redirect message has been received, use the show ip redirects EXEC command.
show ip redirects
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Usage Guidelines
This command displays the default router (gateway) as configured by the ip default-gateway command.
The ip redirects command enables the router to send ICMP Redirect messages.
Examples
The following is sample output from the show ip redirects command:
Router# show ip redirectsDefault gateway is 160.89.80.29Host Gateway Last Use Total Uses Interface131.108.1.111 160.89.80.240 0:00 9 Ethernet0128.95.1.4 160.89.80.240 0:00 4 Ethernet0Router#Related Commands
show ip sockets
To display IP socket information, use the show ip sockets command in privileged EXEC mode or user EXEC mode.
show ip sockets
Syntax Description
This command has no keywords or arguments.
Defaults
No default behavior or values.
Command Modes
Privileged EXEC
User EXECCommand History
Usage Guidelines
Use this command to verify that the socket being used is opening correctly. If there is a local and remote endpoint, a connection is established with the ports indicated.
Examples
The following is sample output from the show ip sockets command:
Router# show ip socketsProto Remote Port Local Port In Out Stat TTY OutputIF17 0.0.0.0 0 171.68.186.193 67 0 0 1 017 171.68.191.135 514 171.68.191.129 1811 0 0 0 017 172.16.135.20 514 171.68.191.1 4125 0 0 0 017 171.68.207.163 49 171.68.186.193 49 0 0 9 017 0.0.0.0 123 171.68.186.193 123 0 0 1 088 0.0.0.0 0 171.68.186.193 202 0 0 0 017 172.16.96.59 32856 171.68.191.1 161 0 0 1 017 --listen-- --any-- 496 0 0 1 0Table 21 describes the significant fields shown in the display.
show ip tcp header-compression
To display statistics about TCP header compression, use the show ip tcp header-compression EXEC command.
show ip tcp header-compression
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following is sample output from the show ip tcp header-compression command:
Router# show ip tcp header-compressionTCP/IP header compression statistics:Interface Serial1: (passive, compressing)Rcvd: 4060 total, 2891 compressed, 0 errors0 dropped, 1 buffer copies, 0 buffer failuresSent: 4284 total, 3224 compressed,105295 bytes saved, 661973 bytes sent1.15 efficiency improvement factorConnect: 16 slots, 1543 long searches, 2 misses, 99% hit ratioFive minute miss rate 0 misses/sec, 0 max misses/secTable 22 describes significant fields shown in the display.
Related Commands
show ip traffic
To display statistics about IP traffic, use the show ip traffic EXEC command.
show ip traffic
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following is sample output from the show ip traffic command:
Router# show ip trafficIP statistics:Rcvd: 98 total, 98 local destination0 format errors, 0 checksum errors, 0 bad hop count0 unknown protocol, 0 not a gateway0 security failures, 0 bad optionsFrags: 0 reassembled, 0 timeouts, 0 too big0 fragmented, 0 couldn't fragmentBcast: 38 received, 52 sentSent: 44 generated, 0 forwarded0 encapsulation failed, 0 no routeICMP statistics:Rcvd: 0 format errors, 0 checksum errors, 0 redirects, 0 unreachable0 echo, 0 echo reply, 0 mask requests, 0 mask replies, 0 quench0 parameter, 0 timestamp, 0 info request, 0 otherSent: 0 redirects, 3 unreachable, 0 echo, 0 echo reply0 mask requests, 0 mask replies, 0 quench, 0 timestamp0 info reply, 0 time exceeded, 0 parameter problemUDP statistics:Rcvd: 56 total, 0 checksum errors, 55 no portSent: 18 total, 0 forwarded broadcastsTCP statistics:Rcvd: 0 total, 0 checksum errors, 0 no portSent: 0 totalEGP statistics:Rcvd: 0 total, 0 format errors, 0 checksum errors, 0 no listenerSent: 0 totalIGRP statistics:Rcvd: 73 total, 0 checksum errorsSent: 26 totalHELLO statistics:Rcvd: 0 total, 0 checksum errorsSent: 0 totalARP statistics:Rcvd: 20 requests, 17 replies, 0 reverse, 0 otherSent: 0 requests, 9 replies (0 proxy), 0 reverseProbe statistics:Rcvd: 6 address requests, 0 address replies0 proxy name requests, 0 otherSent: 0 address requests, 4 address replies (0 proxy)0 proxy name repliesTable 23 describes significant fields shown in the display.
show standby
To display Hot Standby Router Protocol (HSRP) information, use the show standby EXEC command.
show standby [type number [group]] [brief | all]
Syntax Description
Command Modes
EXEC
Command History
Usage Guidelines
If you want to specify a group, you must also specify an interface type and number.
The show standby command does not display information about disabled or learned groups. However, the show standby all command displays information about all groups including disabled and learned groups.
Examples
The following is sample output from the show standby command:
Router# show standbyEthernet0/3 - Group 3Local state is Active, priority 65 (confgd 100)Hellotime 3 sec, holdtime 10 secNext hello sent in 2.276Virtual IP address is 10.20.0.21 configuredActive router is localStandby router is 10.20.0.22 expires in 0:00:07Virtual mac address is 0000.0c07.ac032 state changes, last state change 00:00:21Priority tracking 4 interfaces, 1 up:Interface Decrement StateEthernet0/0 10 UpEthernet0/1 10 Down (IP disabled)Ethernet0/2 10 Down (administratively down)FastEthernet4/0/0 15 Down (no hardware)The following is sample output from the show standby command with a specific interface and the brief keyword:
Router# show standby ethernet0 briefInterface Grp Prio P State Active addr Standby addr Group addrEt0 0 100 Standby 171.69.232.33 local 172.19.48.254Table 24 describes the fields in the display.
Table 24 show standby Field Descriptions
Ethernet0/3 - Group 3
Interface type and number and Hot Standby group number for the interface.
Local state is ...
State of local router; can be one of the following:
•
•
•
•
•
•
priority
Priority value of the router based on the standby priority command.
may preempt
(indicated by P in the brief output)Indicates that the router will attempt to assume control as the active router if its priority is greater than the current active router.
Hellotime
Time between hello packets (in seconds), based on the standby timers command.
holdtime
Time (in seconds) before other routers declare the active or standby router to be down, based on the standby timers command.
Next hello sent in ...
Time in which the Cisco IOS software will send the next hello packet (in hours:minutes:seconds).
Virtual IP address is ... configured
IP address of the current Hot Standby router. The word "configured" indicates that this address is known through the standby ip command. Otherwise, the address was learned dynamically through HSRP hello packets from other routers that do have the HSRP IP address configured.
Active router is ...
Value can be "local" or an IP address. Address of the current active Hot Standby router.
Standby router is ...
Value can be "local" or an IP address. Address of the "standby" router (the router that is next in line to be the Hot Standby router).
expires in
Time (in hours:minutes:seconds) in which the standby router will no longer be the standby router if the local router receives no hello packets from it.
Virtual mac address is ...
The virtual MAC address used in HSRP. This normally defaults to 0000.0C07.ACxy, where xy is the hex value of the group number. Occasionally, you may see a different MAC address that was configured using the standby mac-address command.
Priority tracking ... interfaces...
List of interfaces that are being tracked and their corresponding decrement values and states. Based on the standby track command.
Related Commands
show tcp statistics
To display TCP statistics, use the show tcp statistics EXEC command.
show tcp statistics
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following is sample output from the show tcp statistics command:
Router# show tcp statisticsRcvd: 210 Total, 0 no port0 checksum error, 0 bad offset, 0 too short132 packets (26640 bytes) in sequence5 dup packets (502 bytes)0 partially dup packets (0 bytes)0 out-of-order packets (0 bytes)0 packets (0 bytes) with data after window0 packets after close0 window probe packets, 0 window update packets0 dup ack packets, 0 ack packets with unsend data69 ack packets (3044 bytes)Sent: 175 Total, 0 urgent packets16 control packets (including 1 retransmitted)69 data packets (3029 bytes)0 data packets (0 bytes) retransmitted73 ack only packets (49 delayed)0 window probe packets, 17 window update packets7 Connections initiated, 1 connections accepted, 8 connections established8 Connections closed (including 0 dropped, 0 embryonic dropped)1 Total rxmt timeout, 0 connections dropped in rxmt timeout0 Keepalive timeout, 0 keepalive probe, 0 Connections dropped in keepaliveTable 25 describes significant fields shown in the display.
Related Commands
standby authentication
To configure an authentication string for the Hot Standby Router Protocol (HSRP), use the standby authentication interface configuration command. To delete an authentication string, use the no form of this command.
standby [group-number] authentication text string
no standby [group-number] authentication text string
Syntax Description
Defaults
The default group number is 0. The default string is cisco.
Command Modes
Interface configuration
Command History
Usage Guidelines
HSRP ignores unauthenticated HSRP messages.
The authentication string is sent unencrypted in all HSRP messages. The same authentication string must be configured on all routers and access servers on a cable to ensure interoperation. Authentication mismatch prevents a device from learning the designated Hot Standby IP address and the Hot Standby timer values from other routers configured with HSRP.
When group number 0 is used, no group number is written to NVRAM, providing backward compatibility.
Examples
The following example configures "word" as the authentication string required to allow Hot Standby routers in group 1 to interoperate:
interface ethernet 0standby 1 authentication text wordstandby ip
To activate the Hot Standby Router Protocol (HSRP), use the standby ip interface configuration command. To disable HSRP, use the no form of this command.
standby [group-number] ip [ip-address [secondary]]
no standby [group-number] ip [ip-address]
Syntax Description
Defaults
The default group number is 0.
HSRP is disabled by default.
Command Modes
Interface configuration
Command History
10.0
This command was introduced.
10.3
The group-number argument was added.
11.1
The secondary keyword was added.
Usage Guidelines
The standby ip command activates HSRP on the configured interface. If an IP address is specified, that address is used as the designated address for the Hot Standby group. If no IP address is specified, the designated address is learned through the standby function. For HSRP to elect a designated router, at least one router on the cable must have been configured with, or learned, the designated address. Configuring the designated address on the active router always overrides a designated address that is currently in use.
When the standby ip command is enabled on an interface, the handling of proxy ARP requests is changed (unless proxy ARP was disabled). If the interface's Hot Standby state is active, proxy ARP requests are answered using the Hot Standby group's MAC address. If the interface is in a different state, proxy ARP responses are suppressed.
When group number 0 is used, no group number is written to NVRAM, providing backward compatibility.
Examples
The following example activates HSRP for group 1 on Ethernet interface 0. The IP address used by the Hot Standby group will be learned using HSRP.
interface ethernet 0standby 1 ipIn the following example, all three virtual IP addresses appear in the ARP table using the same (single) virtual MAC address. All three virtual IP addresses are using the same HSRP group (group 0).
ip address 1.1.1.1. 255.255.255.0ip address 1.2.2.2. 255.255.255.0 secondaryip address 1.3.3.3. 255.255.255.0 secondaryip address 1.4.4.4. 255.255.255.0 secondarystandby ip 1.1.1.254standby ip 1.2.2.254 secondarystandby ip 1.3.3.254 secondarystandby mac-address
To specify a virtual MAC address for Hot Standby Router Protocol (HSRP), use the standby mac-address interface configuration command. To revert to the standard virtual MAC address (0000.0C07.ACxy), use the no form of this command.
standby [group-number] mac-address macaddress
no standby [group-number] mac-address
Syntax Description
group-number
(Optional) Group number on the interface for which HSRP is being activated. The default is 0.
macaddress
Media Access Control (MAC) address.
Defaults
If this command is not configured, and the standby use-bia command is not configured, the standard virtual MAC address is used: 0000.0C07.ACxy, where xy is the group number in hexadecimal. This address is specified in RFC 2281, Cisco Hot Standby Router Protocol (HSRP).
Command Modes
Interface configuration
Command History
Usage Guidelines
This command can not be used on a Token Ring Interface.
HSRP is used to help endstations locate the first hop gateway for IP routing. The endstations are configured with a default gateway. However, HSRP can provide first-hop redundancy for other protocols. Some protocols, such as APPN, use the MAC address to identify the first hop for routing purposes. In this case, it is often necessary to be able to specify the virtual MAC address; the virtual IP address is unimportant for these protocols. Use the standby mac-address command to specify the virtual MAC address.
The MAC address specified is used as the virtual MAC address when the router is active.
This command is intended for certain APPN configurations. The parallel terms are as follows:
APPN IP
end node host
network node router or gatewayIn an APPN network, an end node is typically configured with the MAC address of the adjacent network node. Use the standby mac-address command in the routers to set the virtual MAC address to the value used in the end nodes.
Examples
If the end nodes are configured to use 4000.1000.1060 as the MAC address of the network node, the command to configure HSRP group 1 with the virtual MAC address is as follows:
standby 1 mac-address 4000.1000.1060Related Commands
Displays HSRP information.
Configures HSRP to use the burned-in address of the interface as its virtual MAC address.
standby mac-refresh
To change the interval at which packets are sent to refresh the MAC cache when Hot Standby Router Protocol (HSRP) is running over Fiber Distributed Data Interface (FDDI), use the standby mac-refresh interface configuration command. To restore the default value, use the no form of this command.
standby mac-refresh seconds
no standby mac-refresh
Syntax Description
seconds
Number of seconds in the interval at which a packet is sent to refresh the MAC cache. The maximum value is 255 seconds. The default is 10 seconds.
Defaults
The default interval is 10 seconds.
Command Modes
Interface configuration
Command History
Usage Guidelines
This command applies to HSRP running over FDDI only. Packets are sent every 10 seconds to refresh the MAC cache on learning bridges or switches. By default, the MAC cache entries age out in 300 seconds (5 minutes).
All other routers participating in HSRP on the FDDI ring receive the refresh packets, although the packets are intended only for the learning bridge or switch. Use this command to change the interval. Set the interval to 0 if you want to prevent refresh packets (if you have FDDI but do not have a learning bridge or switch).
Examples
The following example changes the MAC refresh interval to 100 seconds. Therefore, a learning bridge would have to miss three packets before the entry ages out.
standby mac-refresh 100standby preempt
To configure Hot Standby Router Protocol (HSRP) priority, preemption, and preemption delay, use the standby preempt or standby priority interface configuration commands. To restore the default values, use the no form of this command.
standby [group-number] priority priority [preempt [delay [minimum | sync] delay]]
standby [group-number] [priority priority] preempt [delay [minimum | sync] delay]
no standby [group-number] priority priority [preempt [delay [minimum | sync] delay]]
no standby [group-number] [priority priority] preempt [delay [minimum | sync] delay]
Syntax Description
Defaults
The default group number is 0.
The default priority is 100.
The default delay is 0 seconds; if the router wants to preempt, it will do so immediately.
Command Modes
Interface configuration
Command History
11.3
This command was introduced.
12.0(2)T
The following keywords were added:
•
•
Usage Guidelines
When using this command, you must specify at least one keyword (priority or preempt), or you can specify both.
When group number 0 is used, no group number is written to NVRAM, providing backward compatibility.
The assigned priority is used to help select the active and standby routers. Assuming preemption is enabled, the router with the highest priority becomes the designated active router. In case of ties, the primary IP addresses are compared, and the higher IP address has priority.
Note that the priority of the device can change dynamically if an interface is configured with the standby track command and another interface on the router goes down.
When a router first comes up, it does not have a complete routing table. If it is configured to preempt, it will become the active router, yet it is unable to provide adequate routing services. This problem is solved by configuring a delay before the preempting router actually preempts the currently active router.
For Mobile IP, if the standby preempt command is used, the preempt synchronization delay must be set or mobility bindings can not be retrieved before the home agent preempts to become active. In the case where one router is designated as the active home agent, the priority is set highest in the HSRP group and preempt is set. Also, the preempt delay sync command is configured so that all bindings are downloaded to the router before it takes the active role. When all bindings are downloaded or when the timer expires, whichever is first, the router becomes active.
Examples
In the following example, the router has a priority of 120 (higher than the default value) and will wait for 300 seconds (5 minutes) before attempting to become the active router:
interface ethernet 0standby ip 172.19.108.254standby priority 120 preempt delay 300Related Commands
Configures an interface so that the Hot Standby priority changes based on the availability of other interfaces.
standby priority
To configure Hot Standby Router Protocol (HSRP) priority, preemption, and preemption delay, use the standby priority or standby preempt interface configuration commands. To restore the default values, use the no form of this command.
standby [group-number] priority priority [preempt [delay [minimum | sync] delay]]
standby [group-number] [priority priority] preempt [delay [minimum | sync] delay]
no standby [group-number] priority priority [preempt [delay [minimum | sync] delay]]
no standby [group-number] [priority priority] preempt [delay [minimum | sync] delay]
Syntax Description
Defaults
The default group number is 0.
The default priority is 100.
The default delay is 0 seconds; if the router wants to preempt, it will do so immediately.
By default, the router that comes up later becomes the standby.
Command Modes
Interface configuration
Command History
11.3
This command was introduced.
12.0(2)T
The following keywords were added:
•
•
Usage Guidelines
When using this command, you must specify at least one keyword (priority or preempt), or you can specify both.
When group number 0 is used, no group number is written to NVRAM, providing backward compatibility.
The assigned priority is used to help select the active and standby routers. Assuming preemption is enabled, the router with the highest priority becomes the designated active router. In case of ties, the primary IP addresses are compared, and the higher IP address has priority.
Note that the priority of the device can change dynamically if an interface is configured with the standby track command and another interface on the router goes down.
When a router first comes up, it does not have a complete routing table. If it is configured to preempt, it will become the active router, yet it is unable to provide adequate routing services. This problem is solved by configuring a delay before the preempting router actually preempts the currently active router.
For Mobile IP, if the standby preempt command is used, the preempt synchronization delay must be set or mobility bindings can not be retrieved before the home agent preempts to become active. In the case where one router is designated as the active home agent, the priority is set highest in the HSRP group and preempt is set. Also, the preempt delay sync command is configured so that all bindings are downloaded to the router before it takes the active role. When all bindings are downloaded or when the timer expires, whichever is first, the router becomes active.
Examples
In the following example, the router has a priority of 120 (higher than the default value) and will wait for 300 seconds (5 minutes) before attempting to become the active router:
interface ethernet 0standby ip 172.19.108.254standby priority 120 preempt delay 300Related Commands
Configures an interface so that the Hot Standby priority changes based on the availability of other interfaces.
standby timers
To configure the time between hellos and the time before other routers declare the active Hot Standby or standby router to be down, use the standby timers interface configuration command. To restore the timers to their default values, use the no form of this command.
standby [group-number] timers [msec] hellotime [msec] holdtime
no standby [group-number] timers [msec] hellotime [msec] holdtime
Syntax Description
Defaults
The default group number is 0.
The default hello interval is 3 seconds.
The default hold time is 10 seconds.
Command Modes
Interface configuration
Command History
Usage Guidelines
The standby timers command configures the time between standby hellos and the time before other routers declare the active or standby router to be down. Routers or access servers on which timer values are not configured can learn timer values from the active or standby router. The timers configured on the active router always override any other timer settings. All routers in a Hot Standby group should use the same timer values. Normally, holdtime is greater than or equal to 3 times the value of hellotime, (holdtime > 3 * hellotime).
The value of the standby timer will not be learned through HSRP hellos if it is less than 1 second.
When group number 0 is used, no group number is written to NVRAM, providing backward compatibility.
Examples
The following example sets, for group number 1 on Ethernet interface 0, the time between hello packets to 5 seconds, and the time after which a router is considered to be down to 15 seconds:
interface ethernet 0standby 1 ipstandby 1 timers 5 15The following example sets, for the Hot Router interface located at 172.19.10.1 on Ethernet interface 0, the time between hello packets to 300 milliseconds, and the time after which a router is considered to be down to 900 milliseconds.
interface ethernet 0standby ip 172.19.10.1standby timers msec 300 msec 900standby track
To configure an interface so that the Hot Standby priority changes based on the availability of other interfaces, use the standby track interface configuration command. To remove the tracking, use the no form of this command.
standby [group-number] track type number [interface-priority]
no standby [group-number] track type number [interface-priority]
Syntax Description
Defaults
The default group number is 0.
The default interface priority is 10.
Command Modes
Interface configuration
Command History
Usage Guidelines
This command ties the router's Hot Standby priority to the availability of its interfaces. It is useful for tracking interfaces that are not configured for the Hot Standby Router Protocol.
When a tracked interface goes down, the Hot Standby priority decreases by 10. If an interface is not tracked, its state changes do not affect the Hot Standby priority. For each interface configured for Hot Standby, you can configure a separate list of interfaces to be tracked.
The optional argument interface-priority specifies how much to decrement the Hot Standby priority by when a tracked interface goes down. When the tracked interface comes back up, the priority is incremented by the same amount.
When multiple tracked interfaces are down, the decrements are cumulative whether configured with interface-priority values or not.
A tracked interface is considered down if the IP address is disabled on that interface.
If HSRP is configured to track an interface, and that interface is physically removed as in the case of an online insertion and removal (OIR) operation, then HSRP will regard the interface as always down. Further, it will not be possible to remove the HSRP interface tracking configuration. To prevent this problem, use the no standby track interface-type interface-number command before you physically remove the interface.
Use the no standby group-number track command to delete all tracking configuration for a group.
When group number 0 is used, no group number is written to NVRAM, providing backward compatibility.
Examples
In the following example, Ethernet interface 1 tracks Ethernet interface 0 and serial interface 0. If one or both of these two interfaces go down, the Hot Standby priority of the router decreases by 10. Because the default Hot Standby priority is 100, the priority becomes 90 when one or both of the tracked interfaces go down.
interface ethernet 1ip address 198.92.72.37 255.255.255.240no ip redirectsstandby track ethernet 0standby track serial 0standby preemptstandby ip 198.92.72.46Related Commands
Displays HSRP information.
Configures HSRP priority, preemption, and preemption delay.
Configures HSRP priority, preemption, and preemption delay.
standby use-bia
To configure Hot Standby Router Protocol (HSRP) to use the burned-in address of the interface as its virtual MAC address, instead of the preassigned MAC address (on Ethernet and Fiber Distributed Data Interface (FDDI)) or the functional address (on Token Ring), use the standby use-bia interface configuration command. To restore the default virtual MAC address, use the no form of this command.
standby use-bia [scope interface]
no standby use-bia
Syntax Description
scope interface
(Optional) Specifies that this command is configured just for the subinterface on which it was entered, instead of the major interface.
Defaults
HSRP uses the preassigned MAC address on Ethernet and FDDI, or the functional address on Token Ring.
Command Modes
Interface configuration
Command History
11.2
This command was introduced.
12.1
The behavior was modified to allow multiple standby groups to be configured for an interface configured with this command
Usage Guidelines
For an interface with this command configured, multiple standby group can be configured. Hosts on the interface need to have a default gateway configured. It is recommended you set the no ip proxy-arp command on the interface. It is desirable to configure the standby use-bia command on a Token Ring interface if there are devices that reject ARP replies with source hardware addresses set to a functional address.
When HSRP runs on a multiple-ring, source-routed bridging environment and the HRSP routers reside on different rings, configuring the standby use-bia command can prevent RIF confusion.
Without the scope interface keywords, the standby use-bia command applies to all sub-interfaces on the major interface. The standby use-bia command may not be configured both with and without the scope interface keywords at the same time.
Examples
In the following example, the burned-in address of Token Ring interface 4/0 will be the virtual MAC address mapped to the virtual IP address:
interface token4/0standby use-biastart-forwarding-agent
To start the forwarding agent, use the start-forwarding-agent CASA-port configuration command.
start-forwarding-agent number [password [timeout]]
Syntax Description
Defaults
The default initial number of affinities is 5000.
The default maximum number of affinities is 30000.
Command Modes
CASA-port configuration
Command History
Usage Guidelines
The forwarding agent must be started before you can configure any port information for the forwarding agent.
Examples
The following example specifies that the forwarding agent will listen for wildcard and fixed affinities on port 1637:
forwarding-agent 1637Related Commands
Specifies the port on which the forwarding agent will listen for wildcard and fixed affinities.
transmit-interface
To assign a transmit interface to a receive-only interface, use the transmit-interface interface configuration command. To return to normal duplex Ethernet interfaces, use the no form of this command.
transmit-interface type number
no transmit-interface
Syntax Description
type
Transmit interface type to be linked with the (current) receive-only interface.
number
Transmit interface number to be linked with the (current) receive-only interface.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
Receive-only interfaces are used commonly with microwave Ethernet links.
Examples
The following example specifies Ethernet interface 0 as a simplex Ethernet interface:
interface ethernet 1ip address 128.9.1.2transmit-interface ethernet 0
