Table Of Contents
ip forward-protocol spanning-tree
ip forward-protocol turbo-flood
IP Addressing Commands
The Internet Protocol (IP) is a packet-based protocol used to exchange data over computer networks. IP handles addressing, fragmentation, reassembly, and protocol demultiplexing. It is the foundation on which all other Internet protocols, collectively referred to as the Internet Protocol suite, are built. IP is a network-layer protocol that contains addressing information and some control information that allows data packets to be routed.
The Transmission Control Protocol (TCP) is built upon the IP layer. TCP is a connection-oriented protocol that specifies the format of data and acknowledgments used in the transfer of data. TCP also specifies the procedures that the computers use to ensure that the data arrives correctly. TCP allows multiple applications on a system to communicate concurrently because it handles all demultiplexing of the incoming traffic among the application programs.
Use the commands in this chapter to configure and monitor the addressing of IP networks. For IP addressing configuration information and examples, refer to the "Configuring IP Addressing" chapter of the Network Protocols Configuration Guide, Part 1.
arp (global)
To add a permanent entry in the Address Resolution Protocol (ARP) cache, use the arp global configuration command. To remove an entry from the ARP cache, use the no form of this command.
arp ip-address hardware-address type [alias]
no arp ip-address hardware-address type [alias]
Syntax Description
Defaults
No entries are permanently installed in the ARP cache.
Command Modes
Global configuration
Command History
Usage Guidelines
The Cisco IOS software uses ARP cache entries to translate 32-bit IP addresses into 48-bit hardware addresses.
Because most hosts support dynamic resolution, you generally do not need to specify static ARP cache entries.
To remove all nonstatic entries from the ARP cache, use the clear arp-cache privileged EXEC command.
Examples
The following is an example of a static ARP entry for a typical Ethernet host:
arp 192.31.7.19 0800.0900.1834 arpaRelated Commands
arp (interface)
To control the interface-specific handling of IP address resolution into 48-bit Ethernet, FDDI, and Token Ring hardware addresses, use the arp interface configuration command. To disable an encapsulation type, use the no form of this command.
arp {arpa | frame-relay | probe | snap | timeout}
no arp {arpa | frame-relay | probe | snap | timeout}
Syntax Description
Defaults
Standard Ethernet-style ARP
Command Modes
Interface configuration
Command History
Usage Guidelines
Unlike most commands that take multiple arguments, arguments to the arp command are not mutually exclusive. Each command enables or disables a specific type of ARP. For example, if you enter the arp arpa command followed by the arp probe command, the Cisco IOS software would send three (two for probe and one for arpa) packets each time it needed to discover a Media Access Control (MAC) address.
The arp probe command allows the software to use the Probe protocol (in addition to ARP) whenever it attempts to resolve an IEEE-802.3 or Ethernet local data link address. The subset of Probe that performs address resolution is called Virtual Address Request and Reply. Using Probe, the software can communicate transparently with Hewlett-Packard IEEE-802.3 hosts that use this type of data encapsulation.
Note
Cisco's support for HP Probe proxy support changed as of Software Release 8.3(2) and subsequent software releases. The no arp probe command is now the default. All interfaces that will use Probe must now be explicitly configured for arp probe.
Given a network protocol address (IP address), the arp frame-relay command determines the corresponding hardware address, which would be a data link connection identifier (DLCI) for frame relay.
The show interfaces EXEC command displays the type of ARP being used on a particular interface. To remove all nonstatic entries from the ARP cache, use the clear arp-cache privileged EXEC command.
Examples
The following example enables probe services:
interface ethernet 0arp probeRelated Commands
Deletes all dynamic entries from the ARP cache.
show interfaces
Displays statistics for all interfaces configured on the router or access server.
arp timeout
To configure how long an entry remains in the ARP cache, use the arp timeout interface configuration command. To restore the default value, use the no form of this command.
arp timeout seconds
no arp timeout seconds
Syntax Description
seconds
Time (in seconds) that an entry remains in the ARP cache. A value of zero means that entries are never cleared from the cache.
Defaults
14400 seconds (4 hours)
Command Modes
Interface configuration
Command History
Usage Guidelines
This command is ignored when issued on interfaces that do not use ARP. The show interfaces EXEC command displays the ARP timeout value. The value follows the "Entry Timeout:" heading, as seen in this sample show interfaces display:
ARP type: ARPA, PROBE, Entry Timeout: 14400 secExamples
The following example sets the ARP timeout to 12000 seconds to allow entries to time out more quickly than the default:
interface ethernet 0arp timeout 12000Related Commands
show interfaces
Displays statistics for all interfaces configured on the router or access server.
clear arp-cache
To delete all dynamic entries from the ARP cache, to clear the fast-switching cache, and to clear the IP route cache, use the clear arp-cache EXEC command.
clear arp-cache
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following example removes all dynamic entries from the ARP cache and clears the fast-switching cache:
clear arp-cacheRelated Commands
Adds a permanent entry in the ARP cache.
Controls the interface-specific handling of IP address resolution into 48-bit Ethernet, FDDI, and Token Ring hardware addresses.
clear host
To delete entries from the host-name-and-address cache, use the clear host EXEC command.
clear host {name | *}
Syntax Description
Command Modes
EXEC
Command History
Usage Guidelines
The host name entries will not be removed from nonvolatile random-access memory (NVRAM), but will be cleared in running memory.
Examples
The following example clears all entries from the host name-and-address cache:
clear host *Related Commands
clear ip nat translation
To clear dynamic Network Address Translation (NAT) translations from the translation table, use the clear ip nat translation EXEC command.
clear ip nat translation {* | [inside global-ip local-ip] [outside local-ip global-ip]}
clear ip nat translation protocol inside global-ip global-port local-ip local-port [outside
local-ip global-ip]Syntax Description
Command Modes
EXEC
Command History
Usage Guidelines
Use this command to clear entries from the translation table before they time out.
Examples
The following example shows the NAT entries before and after the UDP entry being cleared:
Router# show ip nat translationPro Inside global Inside local Outside local Outside globaludp 171.69.233.209:1220 192.168.1.95:1220 171.69.2.132:53 171.69.2.132:53tcp 171.69.233.209:11012 192.168.1.89:11012 171.69.1.220:23 171.69.1.220:23tcp 171.69.233.209:1067 192.168.1.95:1067 171.69.1.161:23 171.69.1.161:23Router# clear ip nat translation udp inside 171.69.233.209 1220 192.168.1.95 1220171.69.2.132 53 171.69.2.132 53Router# show ip nat translationPro Inside global Inside local Outside local Outside globaltcp 171.69.233.209:11012 192.168.1.89:11012 171.69.1.220:23 171.69.1.220:23tcp 171.69.233.209:1067 192.168.1.95:1067 171.69.1.161:23 171.69.1.161:23Related Commands
clear ip nhrp
To clear all dynamic entries from the Next Hop Resolution Protocol (NHRP) cache, use the clear ip nhrp EXEC command.
clear ip nhrp
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Usage Guidelines
This command does not clear any static (configured) IP-to-nonbroadcast multiaccess (NBMA) address mappings from the NHRP cache.
Examples
The following example clears all dynamic entries from the NHRP cache for the interface:
clear ip nhrpRelated Commands
clear ip route
To delete routes from the IP routing table, use the clear ip route EXEC command.
clear ip route {network [mask] | *}
Syntax Description
network
Network or subnet address to remove.
mask
(Optional) Subnet address to remove.
*
Removes all routing table entries.
Defaults
All entries are removed.
Command Modes
EXEC
Command History
Examples
The following example removes a route to network 132.5.0.0 from the IP routing table:
clear ip route 132.5.0.0ip address
To set a primary or secondary IP address for an interface, use the ip address interface configuration command. To remove an IP address or disable IP processing, use the no form of this command.
ip address ip-address mask [secondary]
no ip address ip-address mask [secondary]
Syntax Description
Defaults
No IP address is defined for the interface.
Command Modes
Interface configuration
Command History
Usage Guidelines
An interface can have one primary IP address and multiple secondary IP addresses. Packets generated by the Cisco IOS software always use the primary IP address. Therefore, all routers and access servers on a segment should share the same primary network number.
Hosts can determine subnet masks using the Internet Control Message Protocol (ICMP) Mask Request message. Routers respond to this request with an ICMP Mask Reply message.
You can disable IP processing on a particular interface by removing its IP address with the no ip address command. If the software detects another host using one of its IP addresses, it will print an error message on the console.
The optional keyword secondary allows you to specify an unlimited number of secondary addresses. Secondary addresses are treated like primary addresses, except the system never generates datagrams other than routing updates with secondary source addresses. IP broadcasts and ARP requests are handled properly, as are interface routes in the IP routing table.
Secondary IP addresses can be used in a variety of situations. The following are the most common applications:
•
•
•
Note
Note
To transparently bridge IP on an interface, you must do two things:
•
•
To concurrently route and transparently bridge IP on an interface, see the bridge crb command.
Examples
In the following example, 131.108.1.27 is the primary address and 192.31.7.17 and 192.31.8.17 are secondary addresses for Ethernet interface 0:
interface ethernet 0ip address 131.108.1.27 255.255.255.0ip address 192.31.7.17 255.255.255.0 secondaryip address 192.31.8.17 255.255.255.0 secondaryRelated Commands
ip broadcast-address
To define a broadcast address for an interface, use the ip broadcast-address interface configuration command. To restore the default IP broadcast address, use the no form of this command.
ip broadcast-address [ip-address]
no ip broadcast-address [ip-address]
Syntax Description
Defaults
Default address: 255.255.255.255 (all ones)
Command Modes
Interface configuration
Command History
Examples
The following example specifies an IP broadcast address of 0.0.0.0:
ip broadcast-address 0.0.0.0ip cef traffic-statistics
To change the time interval that controls when NHRP will set up or tear down an SVC, use the ip cef traffic-statistics global configuration command. To restore the default values, use the no form of this command.
ip cef traffic-statistics [load-interval seconds] [update-rate seconds]
no ip cef traffic-statistics
Syntax Description
Defaults
load-interval: 30 seconds
update-rate: 10 seconds
Command Modes
Global configuration
Command History
Usage Guidelines
The thresholds in the ip nhrp trigger-svc command must be exceeded during a certain time interval, which is 30 seconds by default. To change that interval, use the load-interval seconds argument of the ip cef traffic-statistics command.
When NHRP is configured on a CEF switching node with a VIP2 adapter, you must make sure the update-rate is set to 5 seconds.
Other features could also use the ip cef traffic-statistics command; this NHRP feature relies on it.
Examples
In the following example, the triggering and teardown thresholds are calculated based on an average over 120 seconds:
ip cef traffic-statistics load-interval 120Related Commands
Configures when NHRP will set up and tear down an SVC based on aggregate traffic rates.
ip classless
At times the router might receive packets destined for a subnet of a network that has no network default route. To have the Cisco IOS software forward such packets to the best supernet route possible, use the ip classless global configuration command. To disable this feature, use the no form of this command.
ip classless
no ip classless
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Global configuration
Command History
10.0
This command was introduced.
11.3
The default behavior changed from disabled to enabled.
Usage Guidelines
This command allows the software to forward packets that are destined for unrecognized subnets of directly connected networks. The packets are forwarded to the best supernet route.
When the ip classless feature is disabled, the software discards the packets when a router receives packets for a subnet that numerically falls within its subnetwork addressing scheme, if there is no such subnet number in the routing table and there is no network default route.
Note
Examples
The following example prevents the software from forwarding packets destined for an unrecognized subnet to the best supernet possible:
no ip classlessip default-gateway
To define a default gateway (router) when IP routing is disabled, use the ip default-gateway global configuration command. To disable this function, use the no form of this command.
ip default-gateway ip-address
no ip default-gateway ip-address
Syntax Description
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
The Cisco IOS software sends any packets that need the assistance of a gateway to the address you specify. If another gateway has a better route to the requested host, the default gateway sends an ICMP Redirect message back. The ICMP Redirect message indicates which local router the Cisco IOS software should use.
Examples
The following example defines the router on IP address 192.31.7.18 as the default router:
ip default-gateway 192.31.7.18Related Commands
ip directed-broadcast
To enable the translation of directed broadcast to physical broadcasts, use the ip directed-broadcast interface configuration command. To disable this function, use the no form of this command.
ip directed-broadcast [access-list-number] | [extended access-list-number]
no ip directed-broadcast [access-list-number] | [extended access-list-number]
Syntax Description
Defaults
Disabled; all IP directed broadcasts are dropped.
Command Modes
Interface configuration
Command History
10.0
This command was introduced.
12.0
The default behavior changed to directed broadcasts being dropped.
Usage Guidelines
An IP directed broadcast is an IP packet whose destination address is a valid broadcast address for some IP subnet, but which originates from a node that is not itself part of that destination subnet.
A router that is not directly connected to its destination subnet forwards an IP directed broadcast in the same way it would forward unicast IP packets destined to a host on that subnet. When a directed broadcast packet reaches a router that is directly connected to its destination subnet, that packet is "exploded" as a broadcast on the destination subnet. The destination address in the IP header of the packet is rewritten to the configured IP broadcast address for the subnet, and the packet is sent as a link-layer broadcast.
The ip directed-broadcast interface command controls the explosion of directed broadcasts when they reach their target subnets. The command affects only the final transmission of the directed broadcast on its ultimate destination subnet. It does not affect the transit unicast routing of IP directed broadcasts.
If directed broadcast is enabled for an interface, incoming IP packets whose addresses identify them as directed broadcasts intended for the subnet to which that interface is attached will be exploded as broadcasts on that subnet. If an access list has been configured with the ip directed-broadcast command, only directed broadcasts that are permitted by the access list in question will be forwarded; all other directed broadcasts destined for the interface subnet will be dropped.
If the no ip directed-broadcast command has been configured for an interface, directed broadcasts destined for the subnet to which that interface is attached will be dropped, rather than being broadcast.
Note
Examples
The following example enables forwarding of IP directed broadcasts on Ethernet interface 0:
interface ethernet 0ip directed-broadcastRelated Commands
Specifies which protocols and ports the router forwards when forwarding broadcast packets.
ip domain-list
To define a list of default domain names to complete unqualified host names, use the ip domain-list global configuration command. To delete a name from a list, use the no form of this command.
ip domain-list name
no ip domain-list name
Syntax Description
name
Domain name. Do not include the initial period that separates an unqualified name from the domain name.
Defaults
No domain names are defined.
Command Modes
Global configuration
Command History
Usage Guidelines
If there is no domain list, the domain name that you specified with the ip domain-name global configuration command is used. If there is a domain list, the default domain name is not used. The ip domain-list command is similar to the ip domain-name command, except that with ip domain-list you can define a list of domains, each to be tried in turn.
Examples
The following example adds several domain names to a list:
ip domain-list martinez.comip domain-list stanford.eduThe following example adds a name to and then deletes a name from the list:
ip domain-list sunya.eduno ip domain-list stanford.eduRelated Commands
Defines a default domain name to complete unqualified host names (names without a dotted-decimal domain name).
ip domain-lookup
To enable the IP Domain Naming System (DNS)-based host name-to-address translation, use the ip domain-lookup global configuration command. To disable the DNS, use the no form of this command.
ip domain-lookup
no ip domain-lookup
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Global configuration
Command History
Examples
The following example enables the IP Domain Naming System-based host name-to-address translation:
ip domain-lookupRelated Commands
ip domain-name
To define a default domain name that the Cisco IOS software uses to complete unqualified host names (names without a dotted-decimal domain name), use the ip domain-name global configuration command. To disable use of the DNS, use the no form of this command.
ip domain-name name
no ip domain-name
Syntax Description
name
Default domain name used to complete unqualified host names. Do not include the initial period that separates an unqualified name from the domain name.
Defaults
Enabled
Command Modes
Global configuration
Command History
Usage Guidelines
Any IP host name that does not contain a domain name (that is, any name without a dot), will have the dot and cisco.com appended to it before being added to the host table.
Examples
The following example defines cisco.com as the default domain name:
ip domain-name cisco.comRelated Commands
ip forward-protocol
To specify which protocols and ports the router forwards when forwarding broadcast packets, use the ip forward-protocol global configuration command. To remove a protocol or port, use the no form of this command.
ip forward-protocol {udp [port] | nd | sdns}
no ip forward-protocol {udp [port] | nd | sdns}
Syntax Description
Defaults
If an IP helper address is defined, UDP forwarding is enabled on default ports. If UDP flooding is configured, UDP flooding is enabled on the default ports.
If a helper address is specified and UDP forwarding is enabled, broadcast packets destined to the following port numbers are forwarded by default:
•
•
•
•
•
•
•
•
Command Modes
Global configuration
Command History
ip forward-protocol spanning-tree
To permit IP broadcasts to be flooded throughout the internetwork in a controlled fashion, use the ip forward-protocol spanning-tree global configuration command. To disable the flooding of IP broadcasts, use the no form of this command.
ip forward-protocol spanning-tree [any-local-broadcast]
no ip forward-protocol spanning-tree [any-local-broadcast]
Syntax Description
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
A packet must meet the following criteria to be considered for flooding:
•
•
•
•
•
A flooded UDP datagram is given the destination address specified by the ip broadcast-address interface configuration command on the output interface. The destination address can be set to any desired address. Thus, the destination address may change as the datagram propagates through the network. The source address is never changed. The TTL value is decremented.
After a decision has been made to send the datagram out on an interface (and the destination address possibly changed), the datagram is handed to the normal IP output routines and is therefore subject to access lists, if they are present on the output interface.
The ip forward-protocol spanning-tree command uses the database created by the bridging spanning-tree protocol. Therefore, the transparent bridging option must be in the routing software, and bridging must be configured on each interface that is to participate in the flooding in order to support this capability.
If an interface does not have bridging configured, it still will be able to receive broadcasts, but it will never forward broadcasts received on that interface. Also, it will never use that interface to send broadcasts received on a different interface.
If no actual bridging is desired, you can configure a type-code bridging filter that will deny all packet types from being bridged. Refer to the "Configuring Transparent Bridging" chapter in the Bridging and IBM Networking Configuration Guide for more information about using access lists to filter bridged traffic. The spanning-tree database is still available to the IP forwarding code to use for the flooding.
The spanning-tree-based flooding mechanism forwards packets whose contents are all ones (255.255.255.255), all zeros (0.0.0.0), and, if subnetting is enabled, all networks (131.108.255.255 as an example in the network number 131.108.0.0). This mechanism also forward packets whose contents are the zeros version of the all-networks broadcast when subnetting is enabled (for example, 131.108.0.0).
This command is an extension of the ip helper-address interface configuration command, in that the same packets that may be subject to the helper address and forwarded to a single network can now be flooded. Only one copy of the packet will be put on each network segment.
Examples
The following example permits IP broadcasts to be flooded through the internetwork in a controlled fashion:
ip forward-protocol spanning-treeRelated Commands
ip forward-protocol turbo-flood
To speed up flooding of User Datagram Protocol (UDP) datagrams using the spanning-tree algorithm, use the ip forward-protocol turbo-flood global configuration command. To disable this feature, use the no form of this command.
ip forward-protocol turbo-flood
no ip forward-protocol turbo-flood
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
Used in conjunction with the ip forward-protocol spanning-tree global configuration command, this feature is supported over Advanced Research Projects Agency (ARPA)-encapsulated Ethernets, FDDI, and HDLC-encapsulated serials, but is not supported on Token Rings. As long as the Token Rings and the non-HDLC serials are not part of the bridge group being used for UDP flooding, turbo flooding will behave normally.
Examples
The following is an example of a two-port router using this feature:
ip forward-protocol turbo-floodip forward-protocol spanning-tree!interface ethernet 0ip address 128.9.1.1bridge-group 1!interface ethernet 1ip address 128.9.1.2bridge-group 1!bridge 1 protocol decRelated Commands
Specifies which protocols and ports the router forwards when forwarding broadcast packets.
Permits IP broadcasts to be flooded throughout the internetwork in a controlled fashion.
ip helper-address
To have the Cisco IOS software forward User Datagram Protocol (UDP) broadcasts, including BOOTP, received on an interface, use the ip helper-address interface configuration command. To disable the forwarding of broadcast packets to specific addresses, use the no form of this command.
ip helper-address address
no ip helper-address address
Syntax Description
address
Destination broadcast or host address to be used when forwarding UDP broadcasts. There can be more than one helper address per interface.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
Combined with the ip forward-protocol global configuration command, the ip helper-address command allows you to control which broadcast packets and which protocols are forwarded.
Note
One common application that requires helper addresses is Dynamic Host Configuration Protocol (DHCP), which is defined in RFC 1531. DHCP protocol information is carried inside of BOOTP packets. To enable BOOTP broadcast forwarding for a set of clients, configure a helper address on the router interface closest to the client. The helper address should specify the address of the DHCP server. If you have multiple servers, you can configure one helper address for each server. Because BOOTP packets are forwarded by default, DHCP information can now be forwarded by the router. The DHCP server now receives broadcasts from the DHCP clients.
All of the following conditions must be met in order for a UDP or IP packet to be helpered by the ip helper-address command:
•
•
•
•
•
Note
Examples
The following example defines an address that acts as a helper address:
interface ethernet 1ip helper-address 121.24.43.2Related Commands
ip bootp server
Enables the BOOTP service available from hosts on the network.
Specifies which protocols and ports the router forwards when forwarding broadcast packets.
ip host
To define a static host name-to-address mapping in the host cache, use the ip host global configuration command. To remove the name-to-address mapping, use the no form of this command.
ip host name [tcp-port-number] address1 [address2...address8]
no ip host name address1
Syntax Description
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
The first character can be either a letter or a number. If you use a number, the operations you can perform (such as ping) are limited.
Examples
The following example defines two static mappings:
ip host croff 192.31.7.18ip host bisso-gw 10.2.0.2 192.31.7.33ip host-routing
To configure your communication server to act as a terminal server, use the ip host-routing global configuration command. To disable host-based routing, use the no form of this command.
ip host-routing
no ip host-routing
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
The functionality of this command compares to the functionality of the ip routing command as follows:
ip routing—Run the configured routing protocols. If communication servers are not configured do not send packets.
no ip routing—Do not run routing protocols. If the destination is not on the same subnet, use ARP and depend on proxies.
ip host-routing—Do not run routing protocols. If you are not on the same subnet, use ARP and depend on proxies. This command allows IP routing between the SLIP and PPP hosts attached to the communication server but uses host routing methods to send packets to devices and networks that are not directly attached.
Examples
The following example uses the ip host-routing command to configure the communication server to act as a terminal server:
ip host-routingRelated Commands
Defines a static host name-to-address mapping in the host cache.
Enables IP routing.
ip hp-host
To enter into the host table the host name of an HP host to be used for HP Probe Proxy service, use the ip hp-host global configuration command. To remove a host name, use the no form of this command.
ip hp-host hostname ip-address
no ip hp-host hostname ip-address
Syntax Description
Defaults
No host names are defined.
Command Modes
Global configuration
Command History
Usage Guidelines
To use the HP Proxy service, you must first enter the host name of the HP host into the host table using this command.
Examples
The following example specifies an HP host's name and address, and then enables Probe Proxy:
ip hp-host BCWjo 131.108.1.27interface ethernet 0ip probe proxyRelated Commands
Enables the HP Probe Proxy support, which allows the Cisco IOS software to respond to HP Probe Proxy Name requests.
ip irdp
To enable ICMP Router Discovery Protocol (IRDP) processing on an interface, use the ip irdp interface configuration command. To disable IRDP routing, use the no form of this command.
ip irdp [multicast | holdtime seconds | maxadvertinterval seconds | minadvertinterval
seconds | preference number | address address [number]]no ip irdp
Syntax Description
Defaults
Disabled
When enabled, IRDP uses these defaults:
•
•
•
•
Command Modes
Interface configuration
Command History
Usage Guidelines
If you change maxadvertinterval, the other two values also change, so it is important to change maxadvertinterval first before changing either holdtime or minadvertinterval.
The ip irdp multicast command allows for compatibility with Sun Microsystems Solaris, which requires IRDP packets to be sent out as multicasts. Many implementations cannot receive these multicasts; ensure end-host ability before using this command.
Examples
The following example sets the various IRDP processes:
! enable irdp on interface Ethernet 0interface ethernet 0 ip irdp ! send IRDP advertisements to the multicast addressip irdp multicast ! increase router preference from 100 to 50ip irdp preference 50 ! set maximum time between advertisements to 400 secsip irdp maxadvertinterval 400 ! set minimum time between advertisements to 100 secsip irdp minadvertinterval 100 ! advertisements are good for 6000 secondsip irdp holdtime 6000 ! proxy-advertise 131.108.14.5 with default router preferenceip irdp address 131.108.14.5 ! proxy-advertise 131.108.14.6 with preference of 50ip irdp address 131.108.14.6 50Related Commands
ip mobile arp
To enable local-area mobility, use the ip mobile arp interface configuration command. To disable local-area mobility, use the no form of this command.
ip mobile arp [timers keepalive hold-time] [access-group access-list-number | name]
no ip mobile arp [timers keepalive hold-time] [access-group access-list-number | name]
Syntax Description
Defaults
Local-area mobility is disabled.
If you enable local-area mobility:
keepalive: 5 minutes (300 seconds)
hold-time: 15 minutes (900 seconds)Command Modes
Interface configuration
Command History
Usage Guidelines
Local-area mobility is supported on Ethernet, Token Ring, and FDDI interfaces only.
To create larger mobility areas, you must first redistribute the mobile routes into your Interior Gateway Protocol (IGP). The IGP must support host routes. You can use Enhanced IGRP, OSPF, or Intermediate System-to-Intermediate System (IS-IS); you can also use RIP, but this is not recommended. The mobile area must consist of a contiguous set of subnets.
Using an access list to control the list of possible mobile nodes is strongly encouraged. Without an access list, misconfigured hosts can be taken for mobile nodes and disrupt normal operations.
Examples
The following example configures local-area mobility on Ethernet interface 0:
access-list 10 permit 198.92.37.114interface ethernet 0ip mobile arp access-group 10Related Commands
ip name-server
To specify the address of one or more name servers to use for name and address resolution, use the ip name-server global configuration command. To remove the addresses specified, use the no form of this command.
ip name-server server-address1 [server-address2...server-address6]
no ip name-server server-address1 [server-address2...server-address6]
Syntax Description
server-address1
IP addresses of name server.
server-address2...server-address6
(Optional) IP addresses of additional name servers (a maximum of six name servers).
Defaults
No name server addresses are specified.
Command Modes
Global configuration
Command History
Examples
The following example specifies host 131.108.1.111 as the primary name server and host 131.108.1.2 as the secondary server:
ip name-server 131.108.1.111 131.108.1.2This command will be reflected in the configuration file as follows:
ip name-server 131.108.1.111ip name-server 131.108.1.2Related Commands
Enables the IP DNS-based host name-to-address translation.
Defines a default domain name to complete unqualified host names (names without a dotted-decimal domain name).
ip nat
To designate that traffic originating from or destined for the interface is subject to Network Address Translation (NAT), use the ip nat interface configuration command. To prevent the interface from being able to translate, use the no form of this command.
ip nat {inside | outside} | log {translations syslog}
no ip nat {inside | outside} | log {translations syslog}
Syntax Description
Defaults
Traffic leaving or arriving at this interface is not subject to network address translation.
Command Modes
Interface configuration
Command History
Usage Guidelines
Only packets moving between "inside" and "outside" interfaces can be translated. You must specify at least one inside interface and outside interface for each border router where you intend to use NAT.
NAT translations logging can be enabled or disabled with the ip nat log translations syslog command.
Examples
The following example translates between inside hosts addressed from either the 192.168.1.0 or 192.168.2.0 networks to the globally unique 171.69.233.208/28 network:
ip nat pool net-208 171.69.233.208 171.69.233.223 prefix-length 28ip nat inside source list 1 pool net-208!interface ethernet 0ip address 171.69.232.182 255.255.255.240ip nat outside!interface ethernet 1ip address 192.168.1.94 255.255.255.0ip nat inside!access-list 1 permit 192.168.1.0 0.0.0.255access-list 1 permit 192.168.2.0 0.0.0.255Related Commands
ip nat inside destination
To enable Network Address Translation (NAT) of the inside destination address, use the ip nat inside destination global configuration command. To remove the dynamic association to a pool, use the no form of this command.
ip nat inside destination list {access-list-number | name} pool name
no ip nat inside destination list {access-list-number | name}
Syntax Description
Defaults
No inside destination addresses are translated.
Command Modes
Global configuration
Command History
Usage Guidelines
This command has two forms: dynamic and static address translation. The form with an access list establishes dynamic translation. Packets from addresses that match the standard access list are translated using global addresses allocated from the pool named with the ip nat pool command.
Examples
The following example translates between inside hosts addressed to either the 192.168.1.0 or 192.168.2.0 networks to the globally unique 171.69.233.208/28 network:
ip nat pool net-208 171.69.233.208 171.69.233.223 prefix-length 28ip nat inside destination list 1 pool net-208!interface ethernet 0ip address 171.69.232.182 255.255.255.240ip nat outside!interface ethernet 1ip address 192.168.1.94 255.255.255.0ip nat inside!access-list 1 permit 192.168.1.0 0.0.0.255access-list 1 permit 192.168.2.0 0.0.0.255Related Commands
ip nat inside source
To enable Network Address Translation (NAT) of the inside source address, use the ip nat inside source global configuration command. To remove the static translation or remove the dynamic association to a pool, use the no form of this command.
ip nat inside source {list {access-list-number | name} pool name [overload] | static local-ip
global-ip}no ip nat inside source {list {access-list-number | name} pool name [overload] | static local-ip
global-ip}Syntax Description
Defaults
No NAT translation of inside source addresses occurs.
Command Modes
Global configuration
Command History
Usage Guidelines
This command has two forms: dynamic and static address translation. The form with an access list establishes dynamic translation. Packets from addresses that match the standard access list are translated using global addresses allocated from the pool named with the ip nat pool command.
Alternatively, the syntax form with the keyword static establishes a single static translation.
Examples
The following example translates between inside hosts addressed from either the 192.168.1.0 or 192.168.2.0 networks to the globally unique 171.69.233.208/28 network:
ip nat pool net-208 171.69.233.208 171.69.233.223 prefix-length 28ip nat inside source list 1 pool net-208!interface ethernet 0ip address 171.69.232.182 255.255.255.240ip nat outside!interface ethernet 1ip address 192.168.1.94 255.255.255.0ip nat inside!access-list 1 permit 192.168.1.0 0.0.0.255access-list 1 permit 192.168.2.0 0.0.0.255Related Commands
ip nat outside source
To enable Network Address Translation (NAT) of the outside source address, use the ip nat outside source global configuration command. To remove the static entry or the dynamic association, use the no form of this command.
ip nat outside source {list {access-list-number | name} pool name | static global-ip local-ip}
no ip nat outside source {list {access-list-number | name} pool name | static global-ip local-ip}
Syntax Description
Defaults
No translation of source addresses coming from the outside to the inside network occurs.
Command Modes
Global configuration
Command History
Usage Guidelines
You might have IP addresses that are not legal, officially assigned IP addresses. Perhaps you chose IP addresses that officially belong to another network. The case of an address used illegally and legally is called overlapping. You can use NAT to translate inside addresses that overlap with outside addresses. Use this feature if your IP addresses in the stub network happen to be legitimate IP addresses belonging to another network, and you need to communicate with those hosts or routers.
This command has two forms: dynamic and static address translation. The form with an access list establishes dynamic translation. Packets from addresses that match the standard access list are translated using global addresses allocated from the pool named with the ip nat pool command.
Alternatively, the syntax form with the keyword static establishes a single static translation.
Examples
The following example translates between inside hosts addressed from the 9.114.11.0 network to the globally unique 171.69.233.208/28 network. Further packets from outside hosts addressed from the 9.114.11.0 network (the true 9.114.11.0 network) are translated to appear to be from the network 10.0.1.0/24.
ip nat pool net-208 171.69.233.208 171.69.233.223 prefix-length 28 ip nat pool net-10 10.0.1.0 10.0.1.255 prefix-length 24ip nat inside source list 1 pool net-208ip nat outside source list 1 pool net-10!interface ethernet 0ip address 171.69.232.182 255.255.255.240ip nat outside!interface ethernet 1ip address 9.114.11.39 255.255.255.0ip nat inside!access-list 1 permit 9.114.11.0 0.0.0.255Related Commands
ip nat pool
To define a pool of IP addresses for Network Address Translation (NAT), use the ip nat pool global configuration command. To remove one or more addresses from the pool, use the no form of this command.
ip nat pool name start-ip end-ip {netmask netmask | prefix-length prefix-length}[type rotary]
no ip nat pool name start-ip end-ip {netmask netmask | prefix-length prefix-length} [type rotary]
Syntax Description
Defaults
No pool of addresses is defined.
Command Modes
Global configuration
Command History
Usage Guidelines
This command defines a pool of addresses using start address, end address, and either netmask or prefix length. The pool could define either an inside global pool, an outside local pool, or a rotary pool.
Examples
The following example translates between inside hosts addressed from either the 192.168.1.0 or 192.168.2.0 networks to the globally unique 171.69.233.208/28 network:
ip nat pool net-208 171.69.233.208 171.69.233.223 prefix-length 28ip nat inside source list 1 pool net-208!interface ethernet 0ip address 171.69.232.182 255.255.255.240ip nat outside!interface ethernet 1ip address 192.168.1.94 255.255.255.0ip nat inside!access-list 1 permit 192.168.1.0 0.0.0.255access-list 1 permit 192.168.2.0 0.0.0.255Related Commands
ip nat service
To specify a port other than the default port, use the ip nat service global configuration command. To disable the port, use the no form of this command.
ip nat service {list {access-list-number | access-list-name} ftp tcp port port-number}
no ip nat service {list {access-list-number | access-list-name} ftp tcp port port-number}
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
A host with an FTP server using a port other than the default port can have an FTP client using the default FTP control port. When a port other than the default port is configured for an FTP server, Network Address Translation (NAT) prevents FTP control sessions that are using port 21 for that particular server. If an FTP server uses the default port and a port other than the default port, both ports need to be configured using the ip nat service command.
Examples
The following example configures the nonstandard port 2021:
ip nat service list 10 ftp tcp port 2021access-list 10 permit 10.1.1.1The following example configures the standard FTP port 21 and the nonstandard port 2021:
ip nat service list 10 ftp tcp port 21ip nat service list 10 ftp tcp port 2021access-list 10 permit 10.1.1.1Related Commands
ip nat translation
To change the amount of time after which Network Address Translation (NAT) translations time out, use the ip nat translation global configuration command. To disable the timeout, use the no form of this command.
ip nat translation [max-entries number] {timeout | udp-timeout | dns-timeout | tcp-timeout | finrst-timeout | icmp-timeout | pptp-timeout | syn-timeout | port-timeout}
seconds | neverno ip nat translation [max-entries number] {timeout | udp-timeout | dns-timeout | tcp-timeout | finrst-timeout | icmp-timeout | pptp-timeout | syn-timeout | port-timeout}
Syntax Description
Defaults
timeout is 86400 seconds (24 hours)
udp-timeout is 300 seconds (5 minutes)
dns-timeout is 60 seconds (1 minute)
tcp-timeout is 86400 seconds (24 hours)
finrst-timeout is 60 seconds (1 minute)
icmp-timeout is 60 seconds (1 minute)
pptp-timeout is 86400 seconds (24 hours)
syn-timeout is 60 seconds (1 minute)
Command Modes
Global configuration
Command History
Usage Guidelines
When port translation is configured, there is finer control over translation entry timeouts because each entry contains more context about the traffic that is using it. Non-Domain Naming System UDP translations time out after 5 minutes, while DNS times out in 1 minute. TCP translations timeout in 24 hours, unless a RST or FIN is seen on the stream, in which case they will time out in 1 minute.
Examples
The following example causes UDP port translation entries to timeout after 10 minutes:
ip nat translation udp-timeout 600Related Commands
ip netmask-format
To specify the format in which netmasks are displayed in show command output, use the ip netmask-format line configuration command. To restore the default display format, use the no form of this command.
ip netmask-format {bit-count | decimal | hexadecimal}
no ip netmask-format [bit-count | decimal | hexadecimal]
Syntax Description
Defaults
Netmasks are displayed in bitcount format.
Command Modes
Line configuration
Command History
Usage Guidelines
IP uses a 32-bit mask that indicates which address bits belong to the network and subnetwork fields, and which bits belong to the host field. This is called a netmask. By default, show commands display an IP address and then its netmask in dotted decimal notation. For example, a subnet would be displayed as 131.108.11.0 255.255.255.0.
However, you can specify that the display of the network mask appear in hexadecimal format or bit count format instead. The hexadecimal format is commonly used on UNIX systems. The previous example would be displayed as 131.108.11.0 0XFFFFFF00.
The bitcount format for displaying network masks is to append a slash (/) and the total number of bits in the netmask to the address itself. The previous example would be displayed as 131.108.11.0/24.
Examples
The following example configures network masks for the specified line to be displayed in bitcount notation in the output of show commands:
line vty 0 4ip netmask-format bitcountip nhrp authentication
To configure the authentication string for an interface using Next Hop Resolution Protocol (NHRP), use the ip nhrp authentication interface configuration command. To remove the authentication string, use the no form of this command.
ip nhrp authentication string
no ip nhrp authentication [string]
Syntax Description
string
Authentication string configured for the source and destination stations that controls whether NHRP stations allow intercommunication. The string can be up to 8 characters long.
Defaults
No authentication string is configured; the Cisco IOS software adds no authentication option to NHRP packets it generates.
Command Modes
Interface configuration
Command History
Usage Guidelines
All routers configured with NHRP within one logical NBMA network must share the same authentication string.
Examples
In the following example, the authentication string named specialxx must be configured in all devices using NHRP on the interface before NHRP communication occurs:
ip nhrp authentication specialxxip nhrp holdtime
To change the number of seconds that NHRP nonbroadcast, multiaccess (NBMA) addresses are advertised as valid in authoritative NHRP responses, use the ip nhrp holdtime interface configuration command. To restore the default value, use the no form of this command.
ip nhrp holdtime seconds
no ip nhrp holdtime [seconds]
Syntax Description
seconds
Time in seconds that NBMA addresses are advertised as valid in positive authoritative NHRP responses.
Defaults
7200 seconds (2 hours)
Command Modes
Interface configuration
Command History
Usage Guidelines
The ip nhrp holdtime command affects authoritative responses only. The advertised holding time is the length of time the Cisco IOS software tells other routers to keep information that it is providing in authoritative NHRP responses. The cached IP-to-NBMA address mapping entries are discarded after the holding time expires.
The NHRP cache can contain static and dynamic entries. The static entries never expire. Dynamic entries expire regardless of whether they are authoritative or nonauthoritative.
Examples
In the following example, NHRP NBMA addresses are advertised as valid in positive authoritative NHRP responses for one hour:
ip nhrp holdtime 3600ip nhrp interest
To control which IP packets can trigger sending a Next Hop Resolution Protocol (NHRP) Request, use the ip nhrp interest interface configuration command. To restore the default value, use the no form of this command.
ip nhrp interest access-list-number
no ip nhrp interest [access-list-number]
Syntax Description
Defaults
All non-NHRP packets can trigger NHRP requests.
Command Modes
Interface configuration
Command History
Usage Guidelines
Use this command with the access-list command to control which IP packets trigger NHRP Requests.
The ip nhrp interest command controls which packets cause NHRP address resolution to take place; the ip nhrp use command controls how readily the system attempts such address resolution.
Examples
In the following example, any TCP traffic can cause NHRP Requests to be sent, but no other IP packets will cause NHRP Requests:
ip nhrp interest 101access-list 101 permit tcp any anyRelated Commands
ip nhrp map
To statically configure the IP-to-NBMA address mapping of IP destinations connected to a nonbroadcast, multiaccess (NBMA) network, use the ip nhrp map interface configuration command. To remove the static entry from NHRP cache, use the no form of this command.
ip nhrp map ip-address nbma-address
no ip nhrp map ip-address nbma-address
Syntax Description
Defaults
No static IP-to-NBMA cache entries exist.
Command Modes
Interface configuration
Command History
Usage Guidelines
You will probably have to configure at least one static mapping in order to reach the Next Hop Server. Repeat this command to statically configure multiple IP-to-NBMA address mappings.
Examples
In the following example, this station in a multipoint tunnel network is statically configured to be served by two Next Hop Servers 100.0.0.1 and 100.0.1.3. The NBMA address for 100.0.0.1 is statically configured to be 11.0.0.1 and the NBMA address for 100.0.1.3 is 12.2.7.8.
interface tunnel 0ip nhrp nhs 100.0.0.1ip nhrp nhs 100.0.1.3ip nhrp map 100.0.0.1 11.0.0.1ip nhrp map 100.0.1.3 12.2.7.8Related Commands
ip nhrp map multicast
To configure NBMA addresses used as destinations for broadcast or multicast packets to be sent over a tunnel network, use the ip nhrp map multicast interface configuration command. To remove the destinations, use the no form of this command.
ip nhrp map multicast nbma-address
no ip nhrp map multicast nbma-address
Syntax Description
nbma-address
Nonbroadcast, multiaccess (NBMA) address which is directly reachable through the NBMA network. The address format varies depending on the medium you are using.
Defaults
No NBMA addresses are configured as destinations for broadcast or multicast packets.
Command Modes
Interface configuration
Command History
Usage Guidelines
This command applies only to tunnel interfaces.
The command is useful for supporting broadcasts over a tunnel network when the underlying network does not support IP multicast. If the underlying network does support IP multicast, you should use the tunnel destination command to configure a multicast destination for transmission of tunnel broadcasts or multicasts.
When multiple NBMA addresses are configured, the system replicates the broadcast packet for each address.
Examples
In the following example, if a packet is sent to 10.255.255.255, it is replicated to destinations 11.0.0.1 and 11.0.0.2. Addresses 11.0.0.1 and 11.0.0.2 are the IP addresses of two other routers that are part of the tunnel network, but those addresses are their addresses in the underlying network, not the tunnel network. They would have tunnel addresses that are in network 10.0.0.0.
interface tunnel 0ip address 10.0.0.3 255.0.0.0ip nhrp map multicast 11.0.0.1ip nhrp map multicast 11.0.0.2ip nhrp max-send
To change the maximum frequency at which NHRP packets can be sent, use the ip nhrp max-send interface configuration command. To restore this frequency to the default value, use the no form of this command.
ip nhrp max-send pkt-count every interval
no ip nhrp max-send
Syntax Description
pkt-count
Number of packets which can be transmitted in the range from 1 to 65535. Default is 5 packets.
every interval
Time (in seconds) in the range from 10 to 65535. Default is 10 seconds.
Defaults
pkt-count = 5 packets
interval = 10 seconds
Command Modes
Interface configuration
Command History
Usage Guidelines
The software maintains a per-interface quota of NHRP packets that can be transmitted. NHRP traffic, whether locally generated or forwarded, cannot be sent at a rate that exceeds this quota. The quota is replenished at the rate specified by interval.
Examples
In the following example, only 1 NHRP packet can be sent from serial interface 0 each minute:
interface serial 0 ip nhrp max-send 1 every 60Related Commands
ip nhrp network-id
To enable the Next Hop Resolution Protocol (NHRP) on an interface, use the ip nhrp network-id interface configuration command. To disable NHRP on the interface, use the no form of this command.
ip nhrp network-id number
no ip nhrp network-id [number]
Syntax Description
number
Globally unique, 32-bit network identifier for a nonbroadcast, multiaccess (NBMA) network. The range is 1 to 4294967295.
Defaults
NHRP is disabled on the interface.
Command Modes
Interface configuration
Command History
Usage Guidelines
In general, all NHRP stations within one logical NBMA network must be configured with the same network identifier.
Examples
The following example enables NHRP on the interface:
ip nhrp network-id 1ip nhrp nhs
To specify the address of one or more NHRP Next Hop Servers, use the ip nhrp nhs interface configuration command. To remove the address, use the no form of this command.
ip nhrp nhs nhs-address [net-address [netmask]]
no ip nhrp nhs nhs-address [net-address [netmask]]
Syntax Description
Defaults
No Next Hop Servers are explicitly configured, so normal network layer routing decisions are used to forward NHRP traffic.
Command Modes
Interface configuration
Command History
Usage Guidelines
Use this command to specify the address of a Next Hop Server and the networks it serves. Normally, NHRP consults the network layer forwarding table to determine how to forward NHRP packets. When Next Hop Servers are configured, these next hop addresses override the forwarding path that would otherwise be used for NHRP traffic.
For any Next Hop Server that is configured, you can specify multiple networks that it serves by repeating this command with the same nhs-address, but with different net-address IP network addresses.
Examples
In the following example, the Next Hop Server with address 131.108.10.11 serves IP network 10.0.0.0. The mask is 255.0.0.0.
ip nhrp nhs 131.108.10.11 10.0.0.0 255.0.0.0ip nhrp record
To re-enable the use of forward record and reverse record options in NHRP Request and Reply packets, use the ip nhrp record interface configuration command. To suppress the use of such options, use the no form of this command.
ip nhrp record
no ip nhrp record
Syntax Description
This command has no arguments or keywords.
Defaults
Forward record and reverse record options are used in NHRP Request and Reply packets.
Command Modes
Interface configuration
Command History
Usage Guidelines
Forward record and reverse record options provide loop detection and are enabled by default. Using the no form of this command disables this method of loop detection. For another method of loop detection, see the ip nhrp responder command.
Examples
The following example suppresses forward record and reverse record options:
no ip nhrp recordRelated Commands
Designates the primary IP address of which interface the Next Hop Server will use in NHRP Reply packets when the NHRP requester uses the Responder Address option.
ip nhrp responder
To designate which interface's primary IP address the Next Hop Server will use in NHRP Reply packets when the NHRP requestor uses the Responder Address option, use the ip nhrp responder interface configuration command. To remove the designation, use the no form of this command.
ip nhrp responder type number
no ip nhrp responder [type] [number]
Syntax Description
Defaults
The Next Hop Server uses the IP address of the interface where the NHRP Request was received.
Command Modes
Interface configuration
Command History
Usage Guidelines
If an NHRP requestor wants to know which Next Hop Server generates an NHRP Reply packet, it can request that information through the Responder Address option. The Next Hop Server that generates the NHRP Reply packet then complies by inserting its own IP address in the Responder Address option of the NHRP Reply. The Next Hop Server uses the primary IP address of the specified interface.
If an NHRP Reply packet being forwarded by a Next Hop Server contains that Next Hop Server's own IP address, the Next Hop Server generates an Error Indication of type "NHRP Loop Detected" and discards the Reply.
Examples
In the following example, any NHRP requests for the Responder Address will cause this router acting as a Next Hop Server to supply the primary IP address of serial interface 0 in the NHRP Reply packet:
ip nhrp responder serial 0ip nhrp server-only
To configure the interface to operate in NHRP server-only mode, use the ip nhrp server-only interface configuration command. To disable this feature, use the no form of this command.
ip nhrp server-only [non-caching]
no ip nhrp server-only
Syntax Description
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
When the interface is operating in NHRP server-only mode, the interface does not originate NHRP requests or set up an NHRP shortcut SVC.
Examples
The following example configures the interface to operate in server-only mode:
ip nhrp server-onlyip nhrp trigger-svc
To configure when Next Hop Resolution Protocol (NHRP) will set up and tear down an SVC based on aggregate traffic rates, use the ip nhrp trigger-svc interface configuration command. To restore the default thresholds, use the no form of this command.
ip nhrp trigger-svc trigger-threshold teardown-threshold
no ip nhrp trigger-svc
Syntax Description
Defaults
trigger-threshold: 1 kbps
teardown-threshold: 0 kbps
Command Modes
Interface configuration
Command History
Usage Guidelines
The two thresholds are measured during a sampling interval of 30 seconds, by default. To change that interval, use the load-interval seconds argument of the ip cef traffic-statistics command.
Examples
In the following example, the triggering and teardown thresholds are set to 100 kbps and 5 kbps, respectively:
ip nhrp trigger-svc 100 5Related Commands
ip nhrp use
To configure the software so that NHRP is deferred until the system has attempted to send data traffic to a particular destination multiple times, use the ip nhrp use interface configuration command. To restore the default value, use the no form of this command.
ip nhrp use usage-count
no ip nhrp use usage-count
Syntax Description
Defaults
usage-count = 1. The first time a data packet is sent to a destination for which the system determines NHRP can be used, an NHRP request is sent.
Command Modes
Interface configuration
Command History
Usage Guidelines
When the software attempts to transmit a data packet to a destination for which it has determined that NHRP address resolution can be used, an NHRP request for that destination is normally transmitted right away. Configuring the usage-count causes the system to wait until that many data packets have been sent to a particular destination before it attempts NHRP. The usage-count for a particular destination is measured over 1-minute intervals (the NHRP cache expiration interval).
The usage-count applies per destination. So if usage-count is configured to be 3, and 4 data packets are sent toward 10.0.0.1 and 1 packet toward 10.0.0.2, then an NHRP request is generated for 10.0.0.1 only.
If the system continues to need to forward data packets to a particular destination, but no NHRP response has been received, retransmission of NHRP requests are performed. This retransmission occurs only if data traffic continues to be sent to a destination.
The ip nhrp interest command controls which packets cause NHRP address resolution to take place; the ip nhrp use command controls how readily the system attempts such address resolution.
Examples
In the following example, if in the first minute 4 packets are sent to one destination and 5 packets are sent to a second destination, then a single NHRP request is generated for the second destination.
If in the second minute the same traffic is generated and no NHRP responses have been received, then the system retransmits its request for the second destination.
ip nhrp use 5Related Commands
Controls which IP packets can trigger sending a NHRP request.
Changes the maximum frequency at which NHRP packets can be sent.
ip probe proxy
To enable the HP Probe Proxy support, which allows the Cisco IOS software to respond to HP Probe Proxy Name requests, use the ip probe proxy interface configuration command. To disable HP Probe Proxy, use the no form of this command.
ip probe proxy
no ip probe proxy
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
HP Probe Proxy Name requests are typically used at sites that have HP equipment and are already using HP Probe.
To use the HP Proxy service, you must first enter the host name of the HP host into the host table using the ip hp-host global configuration command.
Examples
The following example specifies an HP host's name and address, and then enables Probe Proxy:
ip hp-host BCWjo 131.108.1.27interface ethernet 0ip probe proxyRelated Commands
Enters into the host table the host name of an HP host to be used for HP Probe Proxy service.
ip proxy-arp
To enable proxy ARP on an interface, use the ip proxy-arp interface configuration command. To disable proxy ARP on the interface, use the no form of this command.
ip proxy-arp
no ip proxy-arp
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Interface configuration
Command History
Examples
The following example enables proxy ARP on Ethernet interface 0:
interface ethernet 0ip proxy-arpip routing
To enable IP routing, use the ip routing global configuration command. To disable IP routing, use the no form of this command.
ip routing
no ip routing
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Global configuration
Command History
Usage Guidelines
If Concurrent Routing and Bridging (CRB) is configured, this command is unnecessary because all protocols are bridged by default. If CRB is not configured, configure the no ip routing command to bridge IP.
The ip routing command is disabled on the Cisco VG200 voice over IP gateway.
Examples
The following example enables IP routing:
ip routingip subnet-zero
To enable the use of subnet zero for interface addresses and routing updates, use the ip subnet-zero global configuration command. To restore the default, use the no form of this command.
ip subnet-zero
no ip subnet-zero
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Global configuration
Command History
Usage Guidelines
The ip subnet-zero command provides the ability to configure and route to subnet-zero subnets.
Subnetting with a subnet address of zero is discouraged because of the confusion inherent in having a network and a subnet with indistinguishable addresses.
Examples
The following example enables subnet-zero:
ip subnet-zeroip unnumbered
To enable IP processing on a serial interface without assigning an explicit IP address to the interface, use the ip unnumbered interface configuration command. To disable the IP processing on the interface, use the no form of this command.
ip unnumbered type number
no ip unnumbered type number
Syntax Description
type number
Type and number of another interface on which the router has an assigned IP address. It cannot be another unnumbered interface.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
Whenever the unnumbered interface generates a packet (for example, for a routing update), it uses the address of the specified interface as the source address of the IP packet. It also uses the address of the specified interface in determining which routing processes are sending updates over the unnumbered interface. Restrictions include the following:
•
•
•
•
The interface you specify by the type and number arguments must be enabled (listed as "up" in the show interfaces command display).
If you are configuring IS-IS across a serial line, you should configure the serial interfaces as unnumbered. This allows you to conform with RFC 1195, which states that IP addresses are not required on each interface.
Note
Examples
In the following example, the first serial interface is given Ethernet 0's address:
interface ethernet 0ip address 131.108.6.6 255.255.255.0!interface serial 0ip unnumbered ethernet 0no ip gratuitous-arps
To disable the transmission of gratuitous Address Resolution Protocol (ARP) messages for an address in a local pool, use the no ip gratuitous-arps global configuration command.
no ip gratuitous-arps
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
A Cisco router will send out a gratuitous ARP message when a client connects and negotiates an address over a PPP connection. This transmission occurs even when the client receives the address from a local address pool.
Examples
The following example disables gratuitous arp messages from being sent:
no ip gratuitous-arpsshow arp
To display the entries in the ARP table, use the show arp privileged EXEC command.
show arp
Syntax Description
This command has no arguments or keywords.
Command Modes
Privileged EXEC
Command History
Examples
The following is sample output from the show arp command:
Router# show arpProtocol Address Age (min) Hardware Addr Type InterfaceInternet 131.108.42.112 120 0000.a710.4baf ARPA Ethernet3AppleTalk 4028.5 29 0000.0c01.0e56 SNAP Ethernet2Internet 131.108.42.114 105 0000.a710.859b ARPA Ethernet3AppleTalk 4028.9 - 0000.0c02.a03c SNAP Ethernet2Internet 131.108.42.121 42 0000.a710.68cd ARPA Ethernet3Internet 131.108.36.9 - 0000.3080.6fd4 SNAP TokenRing0AppleTalk 4036.9 - 0000.3080.6fd4 SNAP TokenRing0Internet 131.108.33.9 - 0000.0c01.7bbd SNAP Fddi0Table 3 describes significant fields shown in the first line of output in the display.
show hosts
To display the default domain name, the style of name lookup service, a list of name server hosts, and the cached list of host names and addresses, use the show hosts EXEC command.
show hosts
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following is sample output from the show hosts command:
Router# show hostsDefault domain is CISCO.COMName/address lookup uses domain serviceName servers are 255.255.255.255Host Flag Age Type Address(es)SLAG.CISCO.COM (temp, OK) 1 IP 131.108.4.10CHAR.CISCO.COM (temp, OK) 8 IP 192.31.7.50CHAOS.CISCO.COM (temp, OK) 8 IP 131.108.1.115DIRT.CISCO.COM (temp, EX) 8 IP 131.108.1.111DUSTBIN.CISCO.COM (temp, EX) 0 IP 131.108.1.27DREGS.CISCO.COM (temp, EX) 24 IP 131.108.1.30Table 4 describes significant fields shown in the display.
Related Commands
show ip aliases
To display the IP addresses mapped to TCP ports (aliases) and SLIP addresses, which are treated similarly to aliases, use the show ip aliases EXEC command.
show ip aliases
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Usage Guidelines
To distinguish a SLIP address from a normal alias address, the command output uses the form SLIP TTY1 for the "port" number, where 1 is the auxiliary port.
Examples
The following is sample output from the show ip aliases command:
Router# show ip aliasesIP Address Port131.108.29.245 SLIP TTY1The display lists the IP address and corresponding port number.
Related Commands
show ip arp
To display the Address Resolution Protocol (ARP) cache, where SLIP addresses appear as permanent ARP table entries, use the show ip arp EXEC command.
show ip arp [ip-address] [hostname] [mac-address] [type number]
Syntax Description
Command Modes
EXEC
Usage Guidelines
ARP establishes correspondences between network addresses (an IP address, for example) and LAN hardware addresses (Ethernet addresses). A record of each correspondence is kept in a cache for a predetermined amount of time and then discarded.
Examples
The following is sample output from the show ip arp command:
Router# show ip arpProtocol Address Age(min) Hardware Addr Type InterfaceInternet 171.69.233.22 9 0000.0c59.f892 ARPA Ethernet0/0Internet 171.69.233.21 8 0000.0c07.ac00 ARPA Ethernet0/0Internet 171.69.233.19 - 0000.0c63.1300 ARPA Ethernet0/0Internet 171.69.233.30 9 0000.0c36.6965 ARPA Ethernet0/0Internet 172.19.168.11 - 0000.0c63.1300 ARPA Ethernet0/0Internet 172.19.168.254 9 0000.0c36.6965 ARPA Ethernet0/0Table 5 describes significant fields shown in the display.
show ip interface
To display the usability status of interfaces configured for IP, use the show ip interface EXEC command.
show ip interface [type number] [brief]
Syntax Description
type
(Optional) Interface type.
number
(Optional) Interface number.
brief
(Optional) Displays a summary of the usability status information for each interface.
Command Modes
EXEC
Command History
Usage Guidelines
The Cisco IOS software automatically enters a directly connected route in the routing table if the interface is usable. A usable interface is one through which the software can send and receive packets. If the software determines that an interface is not usable, it removes the directly connected routing entry from the routing table. Removing the entry allows the software to use dynamic routing protocols to determine backup routes to the network (if any).
If the interface can provide two-way communication, the line protocol is marked "up." If the interface hardware is usable, the interface is marked "up."
If you specify an optional interface type, you will see only information on that specific interface.
If you specify no optional arguments, you will see information on all the interfaces.
When an asynchronous interface is encapsulated with PPP or SLIP, IP fast switching is enabled. A show ip interface command on an asynchronous interface encapsulated with PPP or SLIP displays a message indicating that IP fast switching is enabled.
Examples
The following is sample output from the show ip interface command:
Router# show ip interfaceEthernet0 is up, line protocol is upInternet address is 192.195.78.24, subnet mask is 255.255.255.240Broadcast address is 255.255.255.255Address determined by non-volatile memoryMTU is 1500 bytesHelper address is not setSecondary address 131.192.115.2, subnet mask 255.255.255.0Directed broadcast forwarding is enabledMulticast groups joined: 224.0.0.1 224.0.0.2Outgoing access list is not setInbound access list is not setProxy ARP is enabledSecurity level is defaultSplit horizon is enabledICMP redirects are always sentICMP unreachables are always sentICMP mask replies are never sentIP fast switching is enabledIP fast switching on the same interface is disabledIP SSE switching is disabledRouter Discovery is disabledIP output packet accounting is disabledIP access violation accounting is disabledTCP/IP header compression is disabledProbe proxy name replies are disabledTable 6 describes the fields shown in the display.
show ip irdp
To display IRDP values, use the show ip irdp EXEC command.
show ip irdp
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following is sample output from the show ip irdp command:
Router# show ip irdpEthernet 0 has router discovery enabledAdvertisements will occur between every 450 and 600 seconds.Advertisements are valid for 1800 seconds.Default preference will be 100.--More--Serial 0 has router discovery disabled--More--Ethernet 1 has router discovery disabledAs the display shows, show ip irdp output indicates whether router discovery has been configured for each router interface, and it lists the values of router discovery configurables for those interfaces on which router discovery has been enabled. Explanations for the less self-evident lines of output in the display are as follows:
Advertisements will occur between every 450 and 600 seconds.This indicates the configured minimum and maximum advertising interval for the interface.
Advertisements are valid for 1800 seconds.This indicates the configured holdtime values for the interface.
Default preference will be 100.This indicates the configured (or in this case default) preference value for the interface.
Related Commands
show ip masks
To display the masks used for network addresses and the number of subnets using each mask, use the show ip masks EXEC command.
show ip masks address
Syntax Description
Command Modes
EXEC
Command History
Usage Guidelines
The show ip masks command is useful for debugging when a variable-length subnet mask (VLSM) is used. It shows the number of masks associated with the network and the number of routes for each mask.
Examples
The following is sample output from the show ip masks command:
Router# show ip masks 131.108.0.0Mask Reference count255.255.255.255 2255.255.255.0 3255.255.0.0 1show ip nat statistics
To display Network Address Translation (NAT) statistics, use the show ip nat statistics EXEC command.
show ip nat statistics
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following is sample output from the show ip nat statistics command:
Router# show ip nat statisticsTotal translations: 2 (0 static, 2 dynamic; 0 extended)Outside interfaces: Serial0Inside interfaces: Ethernet1Hits: 135 Misses: 5Expired translations: 2Dynamic mappings:-- Inside Sourceaccess-list 1 pool net-208 refcount 2pool net-208: netmask 255.255.255.240start 171.69.233.208 end 171.69.233.221type generic, total addresses 14, allocated 2 (14%), misses 0Table 7 describes the significant fields in the display.
Related Commands
show ip nat translations
To display active Network Address Translation (NAT) translations, use the show ip nat translations EXEC command.
show ip nat translations [verbose]
Syntax Description
verbose
(Optional) Displays additional information for each translation table entry, including how long ago the entry was created and used.
Command Modes
EXEC
Command History
Examples
The following is sample output from the show ip nat translations command. Without overloading, two inside hosts are exchanging packets with some number of outside hosts.
Router# show ip nat translationsPro Inside global Inside local Outside local Outside global--- 171.69.233.209 192.168.1.95 --- ------ 171.69.233.210 192.168.1.89 --- --With overloading, a translation for a DNS transaction is still active, and translations for two Telnet sessions (from two different hosts) are also active. Note that two different inside hosts appear on the outside with a single IP address.
Router# show ip nat translationsPro Inside global Inside local Outside local Outside globaludp 171.69.233.209:1220 192.168.1.95:1220 171.69.2.132:53 171.69.2.132:53tcp 171.69.233.209:11012 192.168.1.89:11012 171.69.1.220:23 171.69.1.220:23tcp 171.69.233.209:1067 192.168.1.95:1067 171.69.1.161:23 171.69.1.161:23The following is sample output that includes the verbose keyword.
Router# show ip nat translations verbosePro Inside global Inside local Outside local Outside globaludp 171.69.233.209:1220 192.168.1.95:1220 171.69.2.132:53 171.69.2.132:53create 00:00:02, use 00:00:00, flags: extendedtcp 171.69.233.209:11012 192.168.1.89:11012 171.69.1.220:23 171.69.1.220:23create 00:01:13, use 00:00:50, flags: extendedtcp 171.69.233.209:1067 192.168.1.95:1067 171.69.1.161:23 171.69.1.161:23create 00:00:02, use 00:00:00, flags: extendedTable 8 describes the significant fields in the display.
Related Commands
show ip nhrp
To display the Next Hop Resolution Protocol (NHRP) cache, use the show ip nhrp EXEC command.
show ip nhrp [dynamic | static] [type number]
Syntax Description
Command Modes
EXEC
Command History
Examples
The following is sample output from the show ip nhrp command:
Router# show ip nhrp10.0.0.2 255.255.255.255, ATM0/0 created 0:00:43 expire 1:59:16Type: dynamic Flags: authoritativeNBMA address: 11.1111.1111.1111.1111.1111.1111.1111.1111.1111.1110.0.0.1 255.255.255.255, Tunnel0 created 0:10:03 expire 1:49:56Type: static Flags: authoritativeNBMA address: 11.1.1.2Table 9 describes the fields in the display.
Table 9 show ip nhrp Field Descriptions
100.0.0.2 255.255.255.255
IP address and its network mask in the IP-to-NBMA address cache. The mask is currently always 255.255.255.255 because we do not support aggregation of NBMA information through NHRP.
ATM0/0 created 0:00:43
Interface type and number (in this case, ATM slot and port numbers) and how long ago it was created (hours:minutes:seconds).
expire 1:59:16
Time in which the positive and negative authoritative NBMA address will expire (hours:minutes:seconds). This value is based on the ip nhrp holdtime command.
Type
Value can be one of the following:
•
•
Flags
Value can be one of the following:
•
•
•
NBMA address
Nonbroadcast, multiaccess address. The address format is appropriate for the type of network being used (for example, ATM, Ethernet, SMDS, multipoint tunnel).
Related Commands
Statically configures the IP-to-NBMA address mapping of IP destinations connected to an NBMA network.
show ip nhrp traffic
To display Next Hop Resolution Protocol (NHRP) traffic statistics, use the show ip nhrp traffic EXEC command.
show ip nhrp 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 nhrp traffic command:
Router# show ip nhrp trafficTunnel0request packets sent: 2request packets received: 4reply packets sent: 4reply packets received: 2register packets sent: 0register packets received: 0error packets sent: 0error packets received: 0Router#Table 10 describes the fields in the display.
term ip netmask-format
To specify the format in which netmasks are displayed in show command output, use the term ip netmask-format EXEC command. To restore the default display format, use the no form of this command.
term ip netmask-format {bitcount | decimal | hexadecimal}
term no ip netmask-format [bitcount | decimal | hexadecimal]
Syntax Description
Defaults
Netmasks are displayed in dotted decimal format.
Command Modes
EXEC
Command History
Usage Guidelines
IP uses a 32-bit mask that indicates which address bits belong to the network and subnetwork fields, and which bits belong to the host field. This is called a netmask. By default, show commands display an IP address and then its netmask in dotted decimal notation. For example, a subnet would be displayed as 131.108.11.55 255.255.255.0.
However, you can specify that the display of the network mask appear in hexadecimal format or bit count format instead. The hexadecimal format is commonly used on UNIX systems. The previous example would be displayed as 131.108.11.55 0XFFFFFF00.
The bitcount format for displaying network masks is to append a slash (/) and the total number of bits in the netmask to the address itself. The previous example would be displayed as 131.108.11.55/24.
Examples
The following example specifies that network masks for the session be displayed in bitcount notation in the output of show commands:
term ip netmask-format bitcounttunnel mode
To set the encapsulation mode for the tunnel interface, use the tunnel mode interface configuration command. To set to the default, us the no form of this command.
tunnel mode {aurp | cayman | dvmrp | eon | gre ip [multipoint] | ipip | nos}
no tunnel mode
Syntax Description
Defaults
GRE tunneling
Command Modes
Interface configuration
Command History
Usage Guidelines
You cannot have two tunnels using the same encapsulation mode with exactly the same source and destination address. The workaround is to create a loopback interface and source packets off of the loopback interface.
Cayman tunneling implements tunneling as designed by Cayman Systems. This enables our routers and access servers to interoperate with Cayman GatorBoxes. With Cayman tunneling, you can establish tunnels between two routers or between our device and a GatorBox. When using Cayman tunneling, you must not configure the tunnel with an AppleTalk network address. This means that there is no way to ping the other end of the tunnel.
Use Distance Vector Multicast Routing Protocol (DVMRP) when a router connects to an mrouted router to run DVMRP over a tunnel. It is required to configure Protocol-Independent Multicast (PIM) and an IP address on a DVMRP tunnel.
Generic routing encapsulation (GRE) tunneling can be done between our routers and access servers only. When using GRE tunneling for AppleTalk, you configure the tunnel with an AppleTalk network address. This means that you can ping the other end of the tunnel.
Examples
For multipoint GRE tunnels, a tunnel key must be configured. Unlike other tunnels, the tunnel destination is optional. However, if the tunnel destination is supplied, it must map to an IP multicast address.
The following example enables Cayman tunneling:
interface tunnel 0tunnel source ethernet 0tunnel destination 131.108.164.19tunnel mode caymanThe following example enables GRE tunneling:
interface tunnel 0appletalk cable-range 4160-4160 4160.19appletalk zone Engineeringtunnel source ethernet 0tunnel destination 131.108.164.19tunnel mode gre ip
