Table Of Contents
Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
Contents
Prerequisites for Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
Restriction for Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
Restrictions for Implementing ACL-Based Forwarding on Cisco IOS XR Software
Information About Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
Cisco IOS XR Access Lists and Prefix Lists Feature Highlights
Purpose of IP Access Lists
How an IP Access List Works
IP Access List Process and Rules
Helpful Hints for Creating IP Access Lists
Source and Destination Addresses
Wildcard Mask and Implicit Wildcard Mask
Transport Layer Information
IP Access List Entry Sequence Numbering
Sequence Numbering Behavior
IP Access List Logging Messages
Extended Access Lists with Fragment Control
Policy Routing
Comments About Entries in Access Lists
Access Control List Counters
BGP Filtering Using Prefix Lists
How the System Filters Traffic by Prefix List
Information About Implementing ACL-Based Forwarding
ACL-Based Forwarding Overview
ACL-Based Forwarding Functions
How to Implement Access Lists and Prefix Lists on Cisco IOS XR Software
Configuring Extended Access Lists
What to Do Next
Applying Access Lists
Controlling Access to an Interface
Controlling Access to a Line
Configuring Prefix Lists
Configuring Standard Access Lists
What to Do Next
Copying Access Lists
Sequencing Access-List Entries and Revising the Access List
What to Do Next
Copying Prefix Lists
Sequencing Prefix List Entries and Revising the Prefix List
Restrictions
How to Implement ACL-Based Forwarding on Cisco IOS XR Software
Configuring ACL-based Forwarding with Security ACL
Configuring Pure ACL-based Forwarding for ACL
Configuration Examples for Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
Resequencing Entries in an Access List: Example
Adding Entries with Sequence Numbers: Example
Adding Entries Without Sequence Numbers: Example
Configuration Examples for Implementing ACL-Based Forwarding
ACL with Security and ACL-Based Forwarding Access Control Entry: Example
Pure ACL-based Forwarding for ACL: Example
Additional References
Related Documents
Standards
MIBs
RFCs
Technical Assistance
Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
An access control list (ACL) consists of one or more access control entries (ACE) that collectively define the network traffic profile. This profile can then be referenced by Cisco IOS XR software features such as traffic filtering, route filtering, QoS classification, and access control. Each ACL includes an action element (permit or deny) and a filter element based on criteria such as source address, destination address, protocol, and protocol-specific parameters.
Prefix lists are used in route maps and route filtering operations and can be used as an alternative to access lists in many Border Gateway Protocol (BGP) route filtering commands. A prefix is a portion of an IP address, starting from the far left bit of the far left octet. By specifying exactly how many bits of an address belong to a prefix, you can then use prefixes to aggregate addresses and perform some function on them, such as redistribution (filter routing updates).
This module describes the new and revised tasks required to implement access lists and prefix lists on your Cisco IOS XR network.
Note 
For a complete description of the access list and prefix list commands listed in this module, refer to the Access List Commands on Cisco IOS XR Software and Prefix List Commands on Cisco IOS XR Software modules in the Cisco IOS XR IP Addresses and Services Command Reference publication. To locate documentation of other commands that appear in this chapter, use the command reference master index, or search online.
Feature History for Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
Release
|
Modification
|
Release 2.0
|
This feature was introduced on the Cisco CRS-1.
|
Release 3.0
|
No modification.
|
Release 3.2
|
This feature was supported on the Cisco XR 12000 Series Router. The command syntax was changed from show ipv4 prefix-list and show ipv6 prefix-list to show prefix-list ipv4 and show prefix-list ipv6. A bulleted item was added to the IP Access List Process and Rules.
|
Release 3.3.0
|
No modification.
|
Release 3.4.0
|
No modification.
|
Release 3.4.1
|
Support was added for ACL-based forwarding on the Cisco CRS-1.
|
Contents
•Prerequisites for Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
•Restriction for Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
•Restrictions for Implementing ACL-Based Forwarding on Cisco IOS XR Software
•Information About Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
•Information About Implementing ACL-Based Forwarding
•How to Implement Access Lists and Prefix Lists on Cisco IOS XR Software
•How to Implement ACL-Based Forwarding on Cisco IOS XR Software
•Configuration Examples for Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
•Configuration Examples for Implementing ACL-Based Forwarding
•Additional References
Prerequisites for Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
The following prerequisite applies to implementing access lists and prefix lists:
You must be in a user group associated with a task group that includes the proper task IDs for access list and prefix list commands. Task IDs for commands are listed with the commands in the Cisco IOS XR IP Addresses and Services Command Reference Guide.
Restriction for Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
The following restriction applies to implementing access lists and prefix lists:
•Resequencing IPv6 prefix lists is not supported.
Restrictions for Implementing ACL-Based Forwarding on Cisco IOS XR Software
The following restrictions apply to implementing ACL-based forwarding (ABF):
•No support for IPv6.
•No support for IPv4 multicast traffic and IPv6.
•No support for Virtual Private Network (VPN) routing and forwarding (VRF) with ACL-based forwarding.
•No support for ACL-based forwarding from a software switching path (for example, IPv4 option packets).
•Support is only on physical interfaces, subinterfaces, and bundles.
•Support is only on instances that are not VRF.
•ACL-based forwarding is an ingress only feature.
Information About Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
To implement access lists and prefix lists, you must understand the following concepts:
•Cisco IOS XR Access Lists and Prefix Lists Feature Highlights
•Purpose of IP Access Lists
•How an IP Access List Works
•IP Access List Entry Sequence Numbering
•IP Access List Logging Messages
•Extended Access Lists with Fragment Control
•Comments About Entries in Access Lists
•Access Control List Counters
•BGP Filtering Using Prefix Lists
•How the System Filters Traffic by Prefix List
Cisco IOS XR Access Lists and Prefix Lists Feature Highlights
This section lists the feature highlights for access and prefix lists.
•Cisco IOS XR software provides the ability to clear counters for an access list or prefix list using a specific sequence number.
•Cisco IOS XR software provides the ability to copy the contents of an existing access list or prefix list to another access list or prefix list.
•Cisco IOS XR software allows users to apply sequence numbers to permit or deny statements and to resequence, add, or remove such statements from a named access list or prefix list.
Only resequencing of IPv4 prefix lists is supported.
•Cisco IOS XR software does not differentiate between standard and extended access lists. Standard access list support is provided for backward compatibility.
•Cisco IOS XR software provides IPv4 ACL-based forwarding to forward IPV4 packets to a next-hop that is specified by the ACL rule.
•Atomic update is supported for both ACL and ACL-based forwarding.
Purpose of IP Access Lists
Access lists perform packet filtering to control which packets move through the network and where. Such controls help to limit network traffic and restrict the access of users and devices to the network. Access lists have many uses, and therefore many commands accept a reference to an access list in their command syntax. Access lists can be used to do the following:
•Filter incoming packets on an interface.
•Filter outgoing packets on an interface.
•Restrict the contents of routing updates.
•Limit debug output based on an address or protocol.
•Control vty access.
•Identify or classify traffic for advanced features, such as congestion avoidance, congestion management, and priority and custom queueing.
How an IP Access List Works
An access list is a sequential list consisting of permit and deny statements that apply to IP addresses and possibly upper-layer IP protocols. The access list has a name by which it is referenced. Many software commands accept an access list as part of their syntax.
An access list can be configured and named, but it is not in effect until the access list is referenced by a command that accepts an access list. Multiple commands can reference the same access list. An access list can control traffic arriving at the router or leaving the router, but not traffic originating at the router.
IP Access List Process and Rules
Use the following process and rules when configuring an IP access list:
•The software tests the source or destination address or the protocol of each packet being filtered against the conditions in the access list, one condition (permit or deny statement) at a time.
•If a packet does not match an access list statement, the packet is then tested against the next statement in the list.
•If a packet and an access list statement match, the remaining statements in the list are skipped and the packet is permitted or denied as specified in the matched statement. The first entry that the packet matches determines whether the software permits or denies the packet. That is, after the first match, no subsequent entries are considered.
•If the access list denies the address or protocol, the software discards the packet and returns an Internet Control Message Protocol (ICMP) Host Unreachable message. ICMP is configurable in the Cisco IOS XR software.
•If no conditions match, the software drops the packet because each access list ends with an unwritten or implicit deny statement. That is, if the packet has not been permitted by the time it was tested against each statement, it is denied.
•The access list should contain at least one permit statement or else all packets are denied.
•Because the software stops testing conditions after the first match, the order of the conditions is critical. The same permit or deny statements specified in a different order could result in a packet being passed under one circumstance and denied in another circumstance.
•If an access list is referenced by name in a command, but the access list does not exist, all packets pass.
•Only one access list per interface, per protocol, per direction is allowed.
•Inbound access lists process packets arriving at the router. Incoming packets are processed before being routed to an outbound interface. An inbound access list is efficient because it saves the overhead of routing lookups if the packet is to be discarded because it is denied by the filtering tests. If the packet is permitted by the tests, it is then processed for routing. For inbound lists, permit means continue to process the packet after receiving it on an inbound interface; deny means discard the packet.
•Outbound access lists process packets before they leave the router. Incoming packets are routed to the outbound interface and then processed through the outbound access list. For outbound lists, permit means send it to the output buffer; deny means discard the packet.
•An access list cannot be removed if that access list has an access group that is in use. Remove the access group from the access list and then remove the access list.
•An access list must exist before you can use the ipv4 access group command.
Helpful Hints for Creating IP Access Lists
Consider the following when creating an IP access list:
•Create the access list before applying it to an interface. An interface to which an empty access list is applied permits all traffic.
•Another reason to configure an access list before applying it is because if you applied a nonexistent access list to an interface and then proceed to configure the access list, the first statement is put into effect, and the implicit deny statement that follows could cause you immediate access problems.
•Organize your access list so that more specific references in a network or subnet appear before more general ones.
•To make the purpose of individual statements more easily understood at a glance, you can write a helpful remark before or after any statement.
Source and Destination Addresses
Source address and destination addresses are two of the most typical fields in an IP packet on which to base an access list. Specify source addresses to control packets from certain networking devices or hosts. Specify destination addresses to control packets being sent to certain networking devices or hosts.
Wildcard Mask and Implicit Wildcard Mask
Address filtering uses wildcard masking to indicate whether the software checks or ignores corresponding IP address bits when comparing the address bits in an access-list entry to a packet being submitted to the access list. By carefully setting wildcard masks, an administrator can select a single or several IP addresses for permit or deny tests.
Wildcard masking for IP address bits uses the number 1 and the number 0 to specify how the software treats the corresponding IP address bits. A wildcard mask is sometimes referred to as an inverted mask, because a 1 and 0 mean the opposite of what they mean in a subnet (network) mask.
•A wildcard mask bit 0 means check the corresponding bit value.
•A wildcard mask bit 1 means ignore that corresponding bit value.
You do not have to supply a wildcard mask with a source or destination address in an access list statement. If you use the host keyword, the software assumes a wildcard mask of 0.0.0.0.
Unlike subnet masks, which require contiguous bits indicating network and subnet to be ones, wildcard masks allow noncontiguous bits in the mask. For IPv6 access lists, only contiguous bits are supported.
Transport Layer Information
You can filter packets on the basis of transport layer information, such as whether the packet is a TCP, UDP, SCTP, ICMP, or IGMP packet.
IP Access List Entry Sequence Numbering
The ability to apply sequence numbers to IP access-list entries simplifies access list changes. Prior to this feature, there was no way to specify the position of an entry within an access list. If a user wanted to insert an entry (statement) in the middle of an existing list, all the entries after the desired position had to be removed, then the new entry was added, and then all the removed entries had to be reentered. This method was cumbersome and error prone.
The IP Access List Entry Sequence Numbering feature allows users to add sequence numbers to access-list entries and resequence them. When you add a new entry, you choose the sequence number so that it is in a desired position in the access list. If necessary, entries currently in the access list can be resequenced to create room to insert the new entry.
Sequence Numbering Behavior
The following details the sequence numbering behavior:
•If entries with no sequence numbers are applied, the first entry is assigned a sequence number of 10, and successive entries are incremented by 10. The maximum sequence number is 2147483646. If the generated sequence number exceeds this maximum number, the following message displays:
Exceeded maximum sequence number.
•If you provide an entry without a sequence number, it is assigned a sequence number that is 10 greater than the last sequence number in that access list and is placed at the end of the list.
•ACL entries can be added without affecting traffic flow and hardware performance.
•If a new access list is entered from global configuration mode, then sequence numbers for that access list are generated automatically.
•Distributed support is provided so that the sequence numbers of entries in the route processor (RP) and line card (LC) are synchronized at all times.
•This feature works with named standard and extended IP access lists. Because the name of an access list can be designated as a number, numbers are acceptable.
IP Access List Logging Messages
Cisco IOS XR software can provide logging messages about packets permitted or denied by a standard IP access list. That is, any packet that matches the access list causes an informational logging message about the packet to be sent to the console. The level of messages logged to the console is controlled by the logging console command in global configuration mode.
The first packet that triggers the access list causes an immediate logging message, and subsequent packets are collected over 5-minute intervals before they are displayed or logged. The logging message includes the access list number, whether the packet was permitted or denied, the source IP address of the packet, and the number of packets from that source permitted or denied in the prior 5-minute interval.
However, you can use the {ipv4 | ipv6} access-list log-update threshold command to set the number of packets that, when they match an access list (and are permitted or denied), cause the system to generate a log message. You might do this to receive log messages more frequently than at 5-minute intervals.
Caution If you set the
update-number argument to 1, a log message is sent right away, rather than caching it; every packet that matches an access list causes a log message. A setting of 1 is not recommended because the volume of log messages could overwhelm the system.
Even if you use the {ipv4 | ipv6} access-list log-update threshold command, the 5-minute timer remains in effect, so each cache is emptied at the end of 5 minutes, regardless of the number of messages in each 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.
Note The logging facility might drop some logging message packets if there are too many to be handled or if more than one logging message is handled in 1 second. This behavior prevents the router from using excessive CPU cycles because of too many logging packets. Therefore, the logging facility should not be used as a billing tool or as an accurate source of the number of matches to an access list.
Extended Access Lists with Fragment Control
Prior to this feature, nonfragmented packets and the initial fragment of a packet were processed by IP extended access lists (if such an access list was applied), but noninitial fragments were permitted by default. The IP Extended Access Lists with Fragment Control feature now allows more granularity of control over noninitial packets. You can specify whether the system examines noninitial IP fragments of packets when applying an IP extended access list.
Because noninitial fragments contain only Layer 3 information, access-list entries containing only Layer 3 information can be and now are applied to noninitial fragments. The fragment has all the information the system requires to filter, so the entry is applied to the fragments.
This feature adds the optional fragments keyword to the following IP access list commands: deny (IPv4), permit (IPv4), deny (IPv6), permit (IPv6). By specifying the fragments keyword in an access-list entry, that particular access-list entry applies only to noninitial fragments of packets; the fragment is either permitted or denied accordingly.
The behavior of access-list entries regarding the presence or absence of the fragments keyword can be summarized as follows:
If the Access-List Entry has...
|
Then..
|
...no fragments keyword and all of the access-list entry information matches,
|
For an access-list entry containing only Layer 3 information:
•The entry is applied to nonfragmented packets, initial fragments, and noninitial fragments.
For an access-list entry containing Layer 3 and Layer 4 information:
•The entry is applied to nonfragmented packets and initial fragments.
–If the entry matches and is a permit statement, the packet or fragment is permitted.
–If the entry matches and is a deny statement, the packet or fragment is denied.
•The entry is also applied to noninitial fragments in the following manner. Because noninitial fragments contain only Layer 3 information, only the Layer 3 portion of an access-list entry can be applied. If the Layer 3 portion of the access-list entry matches, and
–If the entry is a permit statement, the noninitial fragment is permitted.
–If the entry is a deny statement, the next access-list entry is processed.
Note Note that the deny statements are handled differently for noninitial fragments versus nonfragmented or initial fragments.
|
...the fragments keyword and all of the access-list entry information matches,
|
The access-list entry is applied only to noninitial fragments.
Note The fragments keyword cannot be configured for an access-list entry that contains any Layer 4 information.
|
You should not 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. Because 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 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 has 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 fragment counts individually as a packet in access-list accounting and access-list violation counts.
Note The fragments keyword cannot solve all cases involving access lists and IP fragments.
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 Layer 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.
Comments About Entries in Access Lists
You can include comments (remarks) about entries in any named IP access list using the remark access list configuration command. The remarks make the access list easier for the network administrator to understand and scan. Each remark line is limited to 255 characters.
The remark can go before or after a permit or deny statement. You should be consistent about where you put the remark so it is clear which remark describes which permit or deny statement. For example, it would be confusing to have some remarks before the associated permit or deny statements and some remarks after the associated statements. Remarks can be sequenced.
Remember to apply the access list to an interface or terminal line after the access list is created. See the "Applying Access Lists" section for more information.
Access Control List Counters
In Cisco IOS XR software, ACL counters are maintained both in hardware and software. Hardware counters are used for packet filtering applications such as when an access group is applied on an interface. Software counters are used by all the applications mainly involving software packet processing.
Packet filtering makes use of 64-bit hardware counters per ACE. If the same access group is applied on interfaces that are on the same line card in a given direction, the hardware counters for the ACL are shared between two interfaces.
To display the hardware counters for a given access group, use the show access-lists ipv4 access-list-name [hardware {ingress | egress} {location node-id}] command in EXEC mode.
To clear the hardware counters, use the clear access-list ipv4 access-list-name [hardware {ingress | egress} {location node-id}] command in EXEC mode.
Hardware counting is not enabled by default for IPv4 ACLs because of a small performance penalty. To enable hardware counting, use the ipv4 access-group access-list-name {ingress | egress} [hw-count] command in interface configuration mode. This command can be used as desired and counting will be enabled only on the specified interface.
Software counters are updated for the packets processed in software, for example, exception packets punted to the LC CPU for processing, or ACL used by routing protocols, and so on. The counters that are maintained are an aggregate of all the software applications using that ACL. To display software-only ACL counters, use the show access-lists ipv4 access-list-name [sequence number] command in EXEC mode.
All the above information is true for IPv6, except that hardware counting is always enabled; there is no hw-count option in the IPv6 access-group command-line interface (CLI).
BGP Filtering Using Prefix Lists
Prefix lists can be used as an alternative to access lists in many BGP route filtering commands. The advantages of using prefix lists are as follows:
•Significant performance improvement in loading and route lookup of large lists.
•Incremental updates are supported.
•More user friendly CLI. The CLI for using access lists to filter BGP updates is difficult to understand and use because it uses the packet filtering format.
•Greater flexibility.
Before using a prefix list in a command, you must set up a prefix list, and you may want to assign sequence numbers to the entries in the prefix list.
How the System Filters Traffic by Prefix List
Filtering by prefix list involves matching the prefixes of routes with those listed in the prefix list. When there is a match, the route is used. More specifically, whether a prefix is permitted or denied is based upon the following rules:
•An empty prefix list permits all prefixes.
•An implicit deny is assumed if a given prefix does not match any entries of a prefix list.
•When multiple entries of a prefix list match a given prefix, the longest, most specific match is chosen.
Sequence numbers are generated automatically unless you disable this automatic generation. If you disable the automatic generation of sequence numbers, you must specify the sequence number for each entry using the sequence-number argument of the permit and deny commands in either IPv4 or IPv6 prefix list configuration command. Use the no form of the permit or deny command with the sequence-number argument to remove a prefix-list entry.
The show commands include the sequence numbers in their output.
Information About Implementing ACL-Based Forwarding
To implement access lists and prefix lists, you must understand the following concepts:
•ACL-Based Forwarding Overview
•ACL-Based Forwarding Functions
ACL-Based Forwarding Overview
Traffic engineering over an IP or MPLS backbone can be done without MPLS-TE. The ability to divert certain kinds of traffic on top of routing allows you to let only voice traffic travel over certain links, while allowing data traffic to be sent using regular routing.
ACL-based forwarding gives you the ability to choose service from multiple providers for broadcast TV over IP, IP telephony, data, and so on which provides a cafeteria-like access to the Internet. Service providers can divert user traffic to various content providers to the user experience.
ACL-Based Forwarding Functions
ACL-based forwarding (ABF) enables you to configure filters for IPv4 packets. Each packet is based on the information from an IP source or destination address, TCP ports, precedence, DSCP, and so on. If a match occurs, ABF forwards the packet to one of the multiple next hops (up to three). ABF provides an alternative to regular routing by giving the ability to forward a next hop based on packet content that extends beyond the destination IP address.
ABF rule does not apply to "For Us" packet.
By implementing ABF, you can perform the following functions:
•Specify up to three next hops in the ACL rules.
•Forward IPv4 packets that are being forwarded on default routes to the next hop, as specified by the ACL rule.
•Use the existing ACL matching functionality to pick up the next-hop IP address that is based on the ACE configuration. The highest preferred active next-hop IP address is chosen, which is based on the ACE configuration.
•Use the traditional destination IP address forwarding if the ABF next hops are not reachable.
•Use ABF as an ingress-only feature; it is not available for packets switched or originated by the software.
•Specify no rejection when both VRF and ABF configurations are applied on an interface. The ABF configuration is silently ignored by the forwarding software.
How to Implement Access Lists and Prefix Lists on Cisco IOS XR Software
This section contains the following procedures:
•Configuring Extended Access Lists (required)
•Applying Access Lists (required)
•Configuring Prefix Lists (required)
•Configuring Standard Access Lists (optional)
•Copying Access Lists (optional)
•Sequencing Access-List Entries and Revising the Access List (optional)
•Copying Prefix Lists (optional)
•Sequencing Prefix List Entries and Revising the Prefix List (optional)
Configuring Extended Access Lists
This task configures an extended IPv4 or IPv6 access list.
SUMMARY STEPS
1. configure
2. {ipv4 | ipv6} access-list name
3. [sequence-number] remark remark
4. [sequence-number] {permit | deny} source source-wildcard destination destination-wildcard [precedence precedence] [dscp dscp] [fragments] [packet-length operator packet-length value] [log | log-input]
or
[sequence-number] {permit | deny} protocol {source-ipv6-prefix/prefix-length | any | host source-ipv6-address} [operator {port | protocol-port}] {destination-ipv6-prefix/prefix-length | any | host destination-ipv6-address} [operator {port | protocol-port}] [dscp value] [routing] [authen] [destopts] [fragments] [packet-length operator packet-length value] [log | log-input]
5. Repeat Step 4 as necessary, adding statements by sequence number where you planned. Use the no sequence-number command to delete an entry.
6. end
or
commit
7. show access-lists {ipv4 | ipv6} [access-list-name hardware {ingress | egress} {sequence number | location node-id} | summary [access-list-name] | access-list-name [sequence-number] | maximum [detail] [usage {pfilter location node-id}]
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
configure
Example:
RP/0/RP0/CPU0:router# configure
|
Enters global configuration mode.
|
Step 2
|
{ipv4 | ipv6} access-list name
Example:
RP/0/RP0/CPU0:router(config)# ipv4 access-list
acl_1
or
RP/0/RP0/CPU0:router(config)# ipv6 access-list
acl_2
|
Enters either IPv4 or IPv6 access list configuration mode and configures the named access list.
|
Step 3
|
[sequence-number] remark remark
Example:
RP/0/RP0/CPU0:router(config-ipv4-acl)# 10
remark Do not allow user1 to telnet out
|
(Optional) Allows you to comment about a permit or deny statement in a named access list.
•The remark can be up to 255 characters; anything longer is truncated.
•Remarks can be configured before or after permit or deny statements, but their location should be consistent.
|
Step 4
|
[sequence-number] {permit | deny} source
source-wildcard destination
destination-wildcard [precedence precedence]
[dscp dscp] [fragments] [packet-length operator
packet-length value] [log | log-input]
or
[sequence-number] {permit | deny} protocol
{source-ipv6-prefix/prefix-length | any | host
source-ipv6-address} [operator {port |
protocol-port}]
{destination-ipv6-prefix/prefix-length | any |
host destination-ipv6-address} [operator {port
| protocol-port}] [dscp value] [routing]
[authen] [destopts] [fragments] [packet-length
operator packet-length value] [log | log-input]
Example:
RP/0/RP0/CPU0:router(config-ipv4-acl)# 10
permit 172.16.0.0 0.0.255.255
RP/0/RP0/CPU0:router(config-ipv4-acl)# 20 deny
192.168.34.0 0.0.0.255
or
RP/0/RP0/CPU0:router(config-ipv6-acl)# 20
permit icmp any any
RP/0/RP0/CPU0:router(config-ipv6-acl)# 30 deny
tcp any any gt 5000
|
Specifies one or more conditions allowed or denied in IPv4 access list acl_1.
•The optional log keyword causes an information logging message about the packet that matches the entry to be sent to the console.
•The optional log-input keyword provides the same function as the log keyword, except that the logging message also includes the input interface.
or
Specifies one or more conditions allowed or denied in IPv6 access list acl_2.
•Refer to the deny (IPv6) and permit (IPv6) commands for more information on filtering IPv6 traffic based on based on IPv6 option headers and optional, upper-layer protocol type information.
Note Every IPv6 access list has an implicit deny ipv6 any any statement as its last match condition. An IPv6 access list must contain at least one entry for the implicit deny ipv6 any any statement to take effect.
|
Step 5
|
Repeat Step 4 as necessary, adding statements by sequence number where you planned. Use the no sequence-number command to delete an entry.
|
Allows you to revise an access list.
|
Step 6
|
end
or
commit
Example:
RP/0/RP0/CPU0:router(config-ipv4-acl)# end
or
RP/0/RP0/CPU0:router(config-ipv4-acl)# commit
|
Saves configuration changes.
•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
|
Step 7
|
show access-lists {ipv4 | ipv6}
[access-list-name hardware {ingress | egress}
{sequence number | location node-id} | summary
[access-list-name] | access-list-name
[sequence-number] | maximum [detail] [usage
{pfilter location node-id}]
Example:
RP/0/RP0/CPU0:router# show access-lists ipv4
acl_1
|
(Optional) Displays the contents of current IPv4 or IPv6 access lists.
•Use the access-list-name argument to display the contents of a specific access list.
•Use the hardware, ingress or egress, and location or sequence keywords to display the access-list hardware contents and counters for all interfaces that use the specified access list in a given direction (ingress or egress). The access group for an interface must be configured using the ipv4 access-group command for access-list hardware counters to be enabled.
•Use the summary keyword to display a summary of all current IPv4 or IPv6 access-lists.
|
What to Do Next
After creating an access list, you must apply it to a line or interface. See the Applying Access Lists section for information about how to apply an access list.
Applying Access Lists
After you create an access list, you must reference the access list to make it work. Access lists can be applied on either outbound or inbound interfaces. This section describes guidelines on how to accomplish this task for both terminal lines and network interfaces.
Set identical restrictions on all the virtual terminal lines, because a user can attempt to connect to any of them.
For inbound access lists, after receiving a packet, Cisco IOS XR software checks the source address of the packet against the 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. The ICMP message is configurable.
For 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. 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.
When you apply an access list that has not yet been defined to an interface, the software acts as if the access list has not been applied to the interface and accepts all packets. Note this behavior if you use undefined access lists as a means of security in your network.
Controlling Access to an Interface
This task applies an access list to an interface to restrict access to that interface.
Access lists can be applied on either outbound or inbound interfaces.
SUMMARY STEPS
1. configure
2. interface type instance
3. ipv4 access-group access-list-name {ingress | egress} [hw-count]
or
ipv6 access-group access-list-name {ingress | egress}
4. end
or
commit
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
configure
Example:
RP/0/RP0/CPU0:router# configure
|
Enters global configuration mode.
|
Step 2
|
interface type instance
Example:
RP/0/RP0/CPU0:router(config)# interface POS
0/2/0/2
|
Configures an interface and enters interface configuration mode.
•The type argument specifies an interface type. For more information on interface types, use the question mark (?) online help function.
•The instance argument specifies either a physical interface instance or a virtual instance.
–The naming notation for a physical interface instance is rack/slot/module/port. The slash (/) between values is required as part of the notation.
–The number range for a virtual interface instance varies depending on the interface type.
|
Step 3
|
ipv4 access-group access-list-name {ingress |
egress} [hw-count]
or
ipv6 access-group access-list-name {ingress |
egress}
Example:
RP/0/RP0/CPU0:router(config-if)# ipv4
access-group p-in-filter in
RP/0/RP0/CPU0:router(config-if)# ipv4
access-group p-out-filter out
|
Controls access to an interface.
•Use the access-list-name argument to specify a particular IPv4 or IPv6 access list.
•Use the in keyword to filter on inbound packets or the out keyword to filter on outbound packets.
•Use the hw-count keyword to enable hardware counters for the IPv4 access group.
–Hardware counters are automatically enabled for IPv6 access groups.
•This example applies filters on packets inbound and outbound from Packet-over-SONET (POS) interface 0/2/0/2.
|
Step 4
|
end
or
commit
Example:
RP/0/RP0/CPU0:router(config-if)# end
or
RP/0/RP0/CPU0:router(config-if)# commit
|
Saves configuration changes.
•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
|
Controlling Access to a Line
This task applies an access list to a line to control access to that line.
SUMMARY STEPS
1. configure
2. line {aux | console | default | template template-name}
3. access-class list-name {ingress | egress}
4. end
or
commit
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
configure
Example:
RP/0/RP0/CPU0:router# configure
|
Enters global configuration mode.
|
Step 2
|
line {aux | console | default | template
template-name}
Example:
RP/0/RP0/CPU0:router(config)# line default
|
Specifies either the auxiliary, console, default, or a user-defined line template and enters line template configuration mode.
•Line templates are a collection of attributes used to configure and manage physical terminal line connections (the console and auxiliary ports) and vty connections. The following templates are available in Cisco IOS XR software:
–Aux line template—The line template that applies to the auxiliary line.
–Console line template—The line template that applies to the console line.
–Default line template—The default line template that applies to a physical and virtual terminal lines.
–User-defined line templates—User-defined line templates that can be applied to a range of virtual terminal lines.
|
Step 3
|
access-class list-name {ingress | egress}
Example:
RP/0/RP0/CPU0:router(config-line)# access-class
acl_2 out
|
Restricts incoming and outgoing connections using an IPv4 or IPv6 access list.
•In the example, outgoing connections for the default line template are filtered using the IPv6 access list acl_2.
|
Step 4
|
end
or
commit
Example:
RP/0/RP0/CPU0:router(config-line)# end
or
RP/0/RP0/CPU0:router(config-line)# commit
|
Saves configuration changes.
•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
|
Configuring Prefix Lists
This task configures an IPv4 or IPv6 prefix list.
SUMMARY STEPS
1. configure
2. {ipv4 | ipv6} prefix-list name
3. [sequence-number] remark remark
4. [sequence-number] {permit | deny} network/length [ge value] [le value] [eq value]
5. Repeat Step 4 as necessary, adding permit and deny statements by sequence number where you planned. Use the no sequence-number command to delete an entry.
6. end
or
commit
7. show prefix-list ipv4 [name] [sequence-number]
or
show prefix-list ipv6 [name] [sequence-number] [summary]
8. clear {ipv4 | ipv6} prefix-list name [sequence-number]
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
configure
Example:
RP/0/RP0/CPU0:router# configure
|
Enters global configuration mode.
|
Step 2
|
{ipv4 | ipv6} prefix-list name
Example:
RP/0/RP0/CPU0:router(config)# ipv4 prefix-list
pfx_1
or
RP/0/RP0/CPU0:router(config)# ipv6 prefix-list
pfx_2
|
Enters either IPv4 or IPv6 prefix list configuration mode and configures the named prefix list.
•To create a prefix list, you must enter at least one permit or deny clause.
•Use the no {ipv4 | ipv6} prefix-list name command to remove all entries in a prefix list.
|
Step 3
|
[sequence-number] remark remark
Example:
RP/0/RP0/CPU0:router(config-ipv4_pfx)# 10
remark Deny all routes with a prefix of 10/8
RP/0/RP0/CPU0:router(config-ipv4_pfx)# 20 deny
10.0.0.0/8 le 32
|
(Optional) Allows you to comment about the following permit or deny statement in a named prefix list.
•The remark can be up to 255 characters; anything longer is truncated.
•Remarks can be configured before or after permit or deny statements, but their location should be consistent.
|
Step 4
|
[sequence-number] {permit | deny}
network/length [ge value] [le value] [eq value]
Example:
RP/0/RP0/CPU0:router(config-ipv6_pfx)# 20 deny
128.0.0.0/8 eq 24
|
Specifies one or more conditions allowed or denied in the named prefix list.
•This example denies all prefixes matching /24 in 128.0.0.0/8 in prefix list pfx_2.
|
Step 5
|
Repeat Step 4 as necessary. Use the no sequence-number command to delete an entry.
|
Allows you to revise a prefix list.
|
Step 6
|
end
or
commit
Example:
RP/0/RP0/CPU0:router(config-ipv6_pfx)# end
or
RP/0/RP0/CPU0:router(config-ipv6_pfx)# commit
|
Saves configuration changes.
•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
|
Step 7
|
show prefix-list ipv4 [name] [sequence-number]
or
show prefix-list ipv6 [name] [sequence-number]
[summary]
Example:
RP/0/RP0/CPU0:router# show prefix-list ipv4
pfx_1
or
RP/0/RP0/CPU0:router# show prefix-list ipv6
pfx_2 summary
|
(Optional) Displays the contents of current IPv4 or IPv6 prefix lists.
•Use the name argument to display the contents of a specific prefix list.
•Use the sequence-number argument to specify the sequence number of the prefix-list entry.
•Use the summary keyword to display summary output of prefix-list contents.
|
Step 8
|
clear {ipv4 | ipv6} prefix-list name
[sequence-number]
Example:
RP/0/RP0/CPU0:router# clear prefix-list ipv4
pfx_1 30
|
(Optional) Clears the hit count on an IPv4 or IPv6 prefix list.
Note The hit count is a value indicating the number of matches to a specific prefix-list entry.
|
Configuring Standard Access Lists
This task configures a standard IPv4 access list.
Standard access lists use source addresses for matching operations.
SUMMARY STEPS
1. configure
2. ipv4 access-list name
3. [sequence-number] remark remark
4. [sequence-number] {permit | deny} source [source-wildcard] [log | log-input]
5. Repeat Step 4 as necessary, adding statements by sequence number where you planned. Use the no sequence-number command to delete an entry.
6. end
or
commit
7. show access-lists [ipv4 | ipv6] [access-list-name hardware {ingress | egress} {sequence number | location node-id} | summary [access-list-name] | access-list-name [sequence-number] | maximum [detail] [usage {pfilter location node-id}]
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
configure
Example:
RP/0/RP0/CPU0:router# configure
|
Enters global configuration mode.
|
Step 2
|
ipv4 access-list name
Example:
RP/0/RP0/CPU0:router# ipv4 access-list acl_1
|
Enters IPv4 access list configuration mode and configures access list acl_1.
|
Step 3
|
[sequence-number] remark remark
Example:
RP/0/RP0/CPU0:router(config-ipv4-acl)# 10
remark Do not allow user1 to telnet out
|
(Optional) Allows you to comment about the following permit or deny statement in a named access list.
•The remark can be up to 255 characters; anything longer is truncated.
•Remarks can be configured before or after permit or deny statements, but their location should be consistent.
|
Step 4
|
[sequence-number] {permit | deny} source
[source-wildcard] [log | log-input]
Example:
RP/0/RP0/CPU0:router(config-ipv4-acl)# 20
permit 172.16.0.0 0.0.255.255
or
RP/0/RP0/CPU0:router(config-ipv4-acl)# 30 deny
192.168.34.0 0.0.0.255
|
Specifies one or more conditions allowed or denied, which determines whether the packet is passed or dropped.
•Use the source argument to specify the number of network or host from which the packet is being sent.
•Use the optional source-wildcard argument to specify the wildcard bits to be applied to the source.
•The optional log keyword causes an information logging message about the packet that matches the entry to be sent to the console.
•The optional log-input keyword provides the same function as the log keyword, except that the logging message also includes the input interface.
|
Step 5
|
Repeat Step 4 as necessary, adding statements by sequence number where you planned. Use the no sequence-number command to delete an entry.
|
Allows you to revise an access list.
|
Step 6
|
end
or
commit
Example:
RP/0/RP0/CPU0:router(config-ipv4-acl)# end
or
RP/0/RP0/CPU0:router(config-ipv4-acl)# commit
|
Saves configuration changes.
•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
|
Step 7
|
show access-lists [ipv4 | ipv6]
[access-list-name hardware {ingress | egress}
{sequence number | location node-id} | summary
[access-list-name] | access-list-name
[sequence-number] | maximum [detail] [usage
{pfilter location node-id}]
Example:
RP/0/RP0/CPU0:router# show access-lists ipv4
acl_1
|
(Optional) Displays the contents of the named IPv4 access list.
•The contents of an IPv4 standard access list are displayed in extended access-list format.
|
What to Do Next
After creating a standard access list, you must apply it to a line or interface. See the "Applying Access Lists" section for information about how to apply an access list.
Copying Access Lists
This task copies an IPv4 or IPv6 access list.
SUMMARY STEPS
1. copy ipv4 access-list source-acl destination-acl
2. show access-lists {ipv4 | ipv6} [access-list-name hardware {ingress | egress} {sequence number | location node-id} | summary [access-list-name] | access-list-name [sequence-number] | maximum [detail] [usage {pfilter location node-id}]
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
copy {ipv4 | ipv6} access-list source-acl
destination-acl
Example:
RP/0/RP0/CPU0:router# copy ipv6 access-list
list-1 list-2
|
Creates a copy of an existing IPv4 or IPv6 access list.
•Use the source-acl argument to specify the name of the access list to be copied.
•Use the destination-acl argument to specify where to copy the contents of the source access list.
–The destination-acl argument must be a unique name; if the destination-acl argument name exists for an access list, the access list is not copied.
|
Step 2
|
show access-lists {ipv4 | ipv6}
[access-list-name hardware {ingress | egress}
{sequence number | location node-id} | summary
[access-list-name] | access-list-name
[sequence-number] | oor [detail]]
Example:
RP/0/RP0/CPU0:router# show access-lists ipv4
list-2
|
(Optional) Displays the contents of a named IPv4 or IPv6 access list.
•Review the output to see that the destination access list list-2 contains all the information from the source access list list-1.
|
Sequencing Access-List Entries and Revising the Access List
This task shows how to assign sequence numbers to entries in a named access list and how to add or delete an entry to or from an access list. It is assumed that a user wants to revise an access list. Resequencing an access list is optional.
SUMMARY STEPS
1. resequence {ipv4 | ipv6} access-list name [base [increment]]
2. configure
3. {ipv4 | ipv6} access-list name
4. [sequence-number] {permit | deny} source source-wildcard destination destination-wildcard [precedence precedence] [dscp dscp] [fragments] [packet-length operator packet-length value] [log | log-input]
or
[sequence-number] {permit | deny} protocol {source-ipv6-prefix/prefix-length | any | host source-ipv6-address} [operator {port | protocol-port}] {destination-ipv6-prefix/prefix-length | any | host destination-ipv6-address} [operator {port | protocol-port}] [dscp value] [routing] [authen] [destopts] [fragments] [packet-length operator packet-length value] [log | log-input]
5. Repeat Step 4 as necessary, adding statements by sequence number where you planned. Use the no sequence-number command to delete an entry.
6. end
or
commit
7. show access-lists {ipv4 | ipv6} [access-list-name hardware {ingress | egress} {sequence number | location node-id} | summary [access-list-name] | access-list-name [sequence-number] | maximum [detail] [usage {pfilter location node-id}]
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
resequence access-list {ipv4 | ipv6} name [base
[increment]]
Example:
RP/0/RP0/CPU0:router# resequence ipv4
access-list acl_3 20 15
|
(Optional) Resequences the specified IPv4 or IPv6 access list using the starting sequence number and the increment of sequence numbers.
•This example resequences an IPv4 access list named acl_3. The starting sequence number is 20 and the increment is 15. If you do not select an increment, the default increment 10 is used.
|
Step 2
|
configure
Example:
RP/0/RP0/CPU0:router# configure
|
Enters global configuration mode.
|
Step 3
|
{ipv4 | ipv6} access-list name
Example:
RP/0/RP0/CPU0:router(config)# ipv4 access-list
acl_1
or
RP/0/RP0/CPU0:router(config)# ipv6 access-list
acl_2
|
Enters either IPv4 or IPv6 access list configuration mode and configures the named access list.
|
Step 4
|
[sequence-number] {permit | deny} source
source-wildcard destination
destination-wildcard [precedence precedence]
[dscp dscp] [fragments] [packet-length operator
packet-length value] [log | log-input]
or
[sequence-number] {permit | deny} protocol
{source-ipv6-prefix/prefix-length | any | host
source-ipv6-address} [operator {port |
protocol-port}]
{destination-ipv6-prefix/prefix-length | any |
host destination-ipv6-address} [operator {port
| protocol-port}] [dscp value] [routing]
[authen] [destopts] [fragments] [packet-length
operator packet-length value] [log | log-input]
Example:
RP/0/RP0/CPU0:router(config-ipv4-acl)# 10
permit 172.16.0.0 0.0.255.255
RP/0/RP0/CPU0:router(config-ipv4-acl)# 20 deny
192.168.34.0 0.0.0.255
or
RP/0/RP0/CPU0:router(config-ipv6-acl)# 20
permit icmp any any
RP/0/RP0/CPU0:router(config-ipv6-acl)# 30 deny
tcp any any gt 5000
|
Specifies one or more conditions allowed or denied in IPv4 access list acl_1.
•The optional log keyword causes an information logging message about the packet that matches the entry to be sent to the console.
•The optional log-input keyword provides the same function as the log keyword, except that the logging message also includes the input interface.
•This access list happens to use a permit statement first, but a deny statement could appear first, depending on the order of statements you need.
or
Specifies one or more conditions allowed or denied in IPv6 access list acl_2.
•Refer to the permit (IPv6) and deny (IPv6) commands for more information on filtering IPv6 traffic based on IPv6 option headers and upper-layer protocols such as ICMP, TCP, and UDP.
Note Every IPv6 access list has an implicit deny ipv6 any any statement as its last match condition. An IPv6 access list must contain at least one entry for the implicit deny ipv6 any any statement to take effect.
|
Step 5
|
Repeat Step 4 as necessary, adding statements by sequence number where you planned. Use the no sequence-number command to delete an entry.
|
Allows you to revise the access list.
|
Step 6
|
end
or
commit
Example:
RP/0/RP0/CPU0:router(config-ipv4-acl)# end
or
RP/0/RP0/CPU0:router(config-ipv4-acl)# commit
|
Saves configuration changes.
•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
|
Step 7
|
show access-lists [ipv4 | ipv6]
[access-list-name hardware {ingress | egress}
{sequence number | location node-id} | summary
[access-list-name] | access-list-name
[sequence-number] | maximum [detail] [usage
{pfilter location node-id}]
Example:
RP/0/RP0/CPU0:router# show access-lists ipv4
acl_1
|
(Optional) Displays the contents of a named IPv4 or IPv6 access list.
•Review the output to see that the access list includes the updated information.
|
What to Do Next
If your access list is not already applied to an interface or line or otherwise referenced, apply the access list. See the "Applying Access Lists" section for information about how to apply an access list.
Copying Prefix Lists
This task copies an IPv4 or IPv6 prefix list.
SUMMARY STEPS
1. copy prefix-list {ipv4 | ipv6} source-name destination-name
2. show prefix-list ipv4 [name] [sequence-number]
or
show prefix-list ipv6 [name] [sequence-number] [summary]
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
copy prefix-list {ipv4 | ipv6} source-name
destination-name
Example:
RP/0/RP0/CPU0:router# copy prefix-list ipv6
list_1 list_2
|
Creates a copy of an existing IPv4 or IPv6 prefix list.
•Use the source-name argument to specify the name of the prefix list to be copied and the destination-name argument to specify where to copy the contents of the source prefix list.
•The destination-name argument must be a unique name; if the destination-name argument name exists for a prefix list, the prefix list is not copied.
|
Step 2
|
show prefix-list ipv4 [name] [sequence-number]
or
show prefix-list ipv6 [name] [sequence-number]
[summary]
Example:
RP/0/RP0/CPU0:router# show prefix-list ipv6
list_2
|
(Optional) Displays the contents of current IPv4 or IPv6 prefix lists.
•Review the output to see that prefix list list_2 includes the entries from list_1.
|
Sequencing Prefix List Entries and Revising the Prefix List
This task shows how to assign sequence numbers to entries in a named prefix list and how to add or delete an entry to or from a prefix list. It is assumed a user wants to revise a prefix list. Resequencing a prefix list is optional.
Restrictions
Resequencing IPv6 prefix lists is not supported.
SUMMARY STEPS
1. resequence prefix-list ipv4 name [base [increment]]
2. configure
3. {ipv4 | ipv6} prefix-list name
4. [sequence-number] {permit | deny} network/length [ge value] [le value] [eq value]
5. Repeat Step 4 as necessary, adding statements by sequence number where you planned. Use the no sequence-number command to delete an entry.
6. end
or
commit
7. show prefix-list ipv4 [name] [sequence-number]
or
show prefix-list ipv6 [name] [sequence-number] [summary]
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
resequence prefix-list ipv4 name [base
[increment]]
Example:
RP/0/RP0/CPU0:router# resequence prefix-list
ipv4 pfx_1 10 15
|
(Optional) Resequences the named IPv4 prefix list using the starting sequence number and the increment of sequence numbers.
•This example resequences a prefix list named pfx_1. The starting sequence number is 10 and the increment is 15.
|
Step 2
|
configure
Example:
RP/0/RP0/CPU0:router# configure
|
Enters global configuration mode.
|
Step 3
|
{ipv4 | ipv6} prefix-list name
Example:
RP/0/RP0/CPU0:router(config)# ipv6 prefix-list
pfx_2
|
Enters either IPv4 or IPv6 prefix list configuration mode and configures the named prefix list.
|
Step 4
|
[sequence-number] {permit | deny}
network/length [ge value] [le value] [eq value]
Example:
RP/0/RP0/CPU0:router(config-ipv6_pfx)# 15 deny
128.0.0.0/8 eq 24
|
Specifies one or more conditions allowed or denied in the named prefix list.
|
Step 5
|
Repeat Step 4 as necessary, adding statements by sequence number where you planned. Use the no sequence-number command to delete an entry.
|
Allows you to revise the access list.
|
Step 6
|
end
or
commit
Example:
RP/0/RP0/CPU0:router(config-ipv6_pfx)# end
or
RP/0/RP0/CPU0:router(config-ipv6_pfx)# commit
|
Saves configuration changes.
•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before
exiting(yes/no/cancel)?
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
|
Step 7
|
show prefix-list ipv4 [name] [sequence-number]
or
show prefix-list ipv6 [name] [sequence-number]
[summary]
Example:
RP/0/RP0/CPU0:router# show prefix-list ipv6
pfx_2
|
(Optional) Displays the contents of current IPv4 or IPv6 prefix lists.
•Review the output to see that prefix list pfx_2 includes all new information.
|
How to Implement ACL-Based Forwarding on Cisco IOS XR Software
This section contains the following procedures:
•Configuring ACL-based Forwarding with Security ACL
•Configuring Pure ACL-based Forwarding for ACL
Configuring ACL-based Forwarding with Security ACL
Perform this task to configure ACL-based forwarding with security ACL.
SUMMAR STEPS
1. configure
2. ipv4 access-list name
3. [sequence-number] permit protocol source source-wildcard destination destination-wildcard [precedence precedence] [default nexthop [ipv4-address1] [ipv4-address2] [ipv4-address3]] [dscp dscp] [fragments] [packet-length operator packet-length value] [log | log-input] [nexthop [ipv4-address1] [ipv4-address2] [ipv4-address3]] [ttl ttl value1 value2]
4. end
or
commit
5. show access-lists ipv4 [access-list-name hardware {ingress | egress} {sequence number | location node-id} | summary [access-list-name] | access-list-name [sequence-number] | maximum [detail] [usage {pfilter location node-id}
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
configure
Example:
RP/0/RP0/CPU0:router# configure
|
Enters global configuration mode.
|
Step 2
|
ipv4 access-list name
Example:
RP/0/RP0/CPU0:router(config)# ipv4 access-list
security-abf-acl
|
Enters IPv4 access list configuration mode and configures access list security-abf-acl.
|
Step 3
|
[sequence-number] permit protocol source
source-wildcard destination destination-wildcard
[precedence precedence] [default nexthop
[ipv4-address1] [ipv4-address2] [ipv4-address3]]
[dscp dscp] [fragments] [packet-length operator
packet-length value] [log | log-input] [nexthop
[ipv4-address1] [ipv4-address2] [ipv4-address3]]
[ttl ttl value1 value2]
Example:
RP/0/RP0/CPU0:router(config-ipv4-acl)# 10 permit
ipv4 10.0.0.0 0.255.255.255 any nexthop 50.1.1.2
RP/0/RP0/CPU0:router(config-ipv4-acl)# 15 permit
ipv4 30.2.1.0 0.0.0.255 any
RP/0/RP0/CPU0:router(config-ipv4-acl)# 20 permit
ipv4 30.2.0.0 0.0.255.255 any nexthop 40.1.1.2
RP/0/RP0/CPU0:router(config-ipv4-acl)# 25 permit
ipv4 any any
|
Sets the conditions for an IPv4 access list. The configuration example shows how to configure ACL-based forwarding with security ACL.
•The nexthop keyword forwards the specified next hop for this entry.
|
Step 4
|
end
or
commit
Example:
RP/0/RP0/CPU0:router(config-ipv4-acl)# end
or
RP/0/RP0/CPU0:router(config-ipv4-acl)# commit
|
Saves configuration changes.
•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them
before exiting(yes/no/cancel)?
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
|
Step 5
|
show access-list ipv4 [access-list-name hardware
{ingress | egress} {sequence number | location
node-id} | summary [access-list-name] |
access-list-name [sequence-number] | maximum
[detail] [usage {pfilter location node-id}
Example:
RP/0/RP0/CPU0:router# show access-lists ipv4
security-abf-acl
|
Displays the information for ACL software.
|
Configuring Pure ACL-based Forwarding for ACL
Perform this task to configure pure ACL-based forwarding for ACL.
SUMMAR STEPS
1. configure
2. ipv4 access-list name
3. [sequence-number] permit protocol source source-wildcard destination destination-wildcard [precedence precedence] [default nexthop [ipv4-address1] [ipv4-address2] [ipv4-address3]] [dscp dscp] [fragments] [packet-length operator packet-length value] [log | log-input] [nexthop [ipv4-address1] [ipv4-address2] [ipv4-address3]] [ttl ttl value1 value2]
4. end
or
commit
5. show access-lists ipv4 [access-list-name hardware {ingress | egress} {sequence number | location node-id} | summary [access-list-name] | access-list-name [sequence-number] | maximum [detail] [usage {pfilter location node-id}
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
configure
Example:
RP/0/RP0/CPU0:router# configure
|
Enters global configuration mode.
|
Step 2
|
ipv4 access-list name
Example:
RP/0/RP0/CPU0:router(config)# ipv4 access-list
security-abf-acl
|
Enters IPv4 access list configuration mode and configures access list security-abf-acl.
|
Step 3
|
[sequence-number] permit protocol source
source-wildcard destination destination-wildcard
[precedence precedence] [default nexthop
[ipv4-address1] [ipv4-address2] [ipv4-address3]]
[dscp dscp] [fragments] [packet-length operator
packet-length value] [log | log-input] [nexthop
[ipv4-address1] [ipv4-address2] [ipv4-address3]]
[ttl ttl value1 value2]
Example:
RP/0/RP0/CPU0:router(config-ipv4-acl)# 10 permit
ipv4 10.0.0.0 0.255.255.255 any nexthop 50.1.1.2
RP/0/RP0/CPU0:router(config-ipv4-acl)# 15 permit
ipv4 30.2.1.0 0.0.0.255 any
RP/0/RP0/CPU0:router(config-ipv4-acl)# 20 permit
ipv4 30.2.0.0 0.0.255.255 any nexthop 40.1.1.2
RP/0/RP0/CPU0:router(config-ipv4-acl)# 25 permit
ipv4 any any
|
Sets the conditions for an IPv4 access list. The configuration example shows how to configure pure ACL-based forwarding for ACL.
•The nexthop keyword forwards the specified next hop for this entry.
|
Step 4
|
end
or
commit
Example:
RP/0/RP0/CPU0:router(config-ipv4-acl)# end
or
RP/0/RP0/CPU0:router(config-ipv4-acl)# commit
|
Saves configuration changes.
•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them
before exiting(yes/no/cancel)?
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
|
Step 5
|
show access-list ipv4 [access-list-name hardware
{ingress | egress} {sequence number | location
node-id} | summary [access-list-name] |
access-list-name [sequence-number] | maximum
[detail] [usage {pfilter location node-id}
Example:
RP/0/RP0/CPU0:router# show access-lists ipv4
security-abf-acl
|
Displays the information for ACL software.
|
Configuration Examples for Implementing Access Lists and Prefix Lists on Cisco IOS XR Software
This section provides the following configuration examples:
•Resequencing Entries in an Access List: Example
•Adding Entries with Sequence Numbers: Example
•Adding Entries Without Sequence Numbers: Example
Resequencing Entries in an Access List: Example
The following example shows access-list resequencing. The starting value in the resequenced access list is 1, and increment value is 2. The subsequent entries are ordered based on the increment values that users provide, and the range is from 1 to 2147483646.
When an entry with no sequence number is entered, by default it has a sequence number of 10 more than the last entry in the access list.
10 permit ip host 10.3.3.3 host 172.16.5.34
30 permit tcp any host 10.3.3.3
40 permit ip host 10.4.4.4 any
60 permit ip host 172.16.2.2 host 10.3.3.12
70 permit ip host 10.3.3.3 any log
80 permit tcp host 10.3.3.3 host 10.1.2.2
resequence ipv6 access-list acl_1 10 20
10 permit ip host 10.3.3.3 host 172.16.5.34
50 permit tcp any host 10.3.3.3
70 permit ip host 10.4.4.4 any
90 Dynamic test permit ip any any
110 permit ip host 172.16.2.2 host 10.3.3.12
130 permit ip host 10.3.3.3 any log
150 permit tcp host 10.3.3.3 host 10.1.2.2
170 permit ip host 10.3.3.3 any
Adding Entries with Sequence Numbers: Example
In the following example, an new entry is added to IPv4 access list acl_5.
15 permit 10.5.5.5 0.0.0.255
Adding Entries Without Sequence Numbers: Example
The following example shows how an entry with no specified sequence number is added to the end of an access list. When an entry is added without a sequence number, it is automatically given a sequence number that puts it at the end of the access list. Because the default increment is 10, the entry will have a sequence number 10 higher than the last entry in the existing access list.
10 permit ip 1.1.1.0 0.0.0.255 any
20 permit ip 2.2.2.0 0.0.0.255 any
30 permit ip 3.3.3.0 0.0.0.255 any
10 permit ip 1.1.1.0 0.0.0.255 any
20 permit ip 2.2.2.0 0.0.0.255 any
30 permit ip 3.3.3.0 0.0.0.255 any
40 permit ip 4.4.4.0 0.0.0.255 any
Configuration Examples for Implementing ACL-Based Forwarding
This section provides the following configuration examples:
•ACL with Security and ACL-Based Forwarding Access Control Entry: Example
•Pure ACL-based Forwarding for ACL: Example
All configuration examples include a forwarded action nexthop keyword. If the default nexthop keyword is configured, ABF action is taken only if the packets destination pointer look up (PLU) results in hitting a default route. For example, no specific route is specified to the packet destination.
ACL with Security and ACL-Based Forwarding Access Control Entry: Example
The following example shows how to configure ACL with security and ACL-based forwarding access control entry (ACE):
ipv4 access-list security-abf-acl
10 permit ipv4 10.0.0.0 0.255.255.255 any
15 permit ipv4 30.2.0.0 0.0.255.255 any next-hop 40.1.1.2
20 deny ipv4 30.1.0.0 0.0.255.255 any
25 permit ipv4 30.0.0.0 0.255.255.255 any
Note For ACL-based forwarding, the following example is programmed in the hardware after Access List Entry (ACE) 25:
The following methods are used to attach the ACL for both security and ACL-based forwarding ACE to an interface in ingress direction:
•Packets entering an interface with source address 10.x.x.x are forwarded using a traditional forwarding lookup.
•Packets entering an interface with source address 30.2.x.x are forwarded to nexthop 40.1.1.2 (if reachable through FIB).
•Packets entering an interface with source address 30.1.x.x are dropped by security ACE 20.
•All other packets that are entering an interface are dropped by security ACL.
Pure ACL-based Forwarding for ACL: Example
The following example shows how to configure pure ABF for ACL:
ipv4 access-list security-abf-acl
10 permit ipv4 10.0.0.0 0.255.255.255 any next-hop 50.1.1.2
15 permit ipv4 30.2.1.0 0.0.0.255 any
20 permit ipv4 30.2.0.0 0.0.255.255 any next-hop 40.1.1.2
Note For ACL-based forwarding, the following example is programmed at the of ACL in hardware:
Therefore, the following ACE example is important to let other traffic through:
The following methods are used to attach the ACL, which is used only for ACL-based forwarding ACE to an interface in ingress direction:
•Packets entering an interface with source address 10.x.x.x are forwarded to next-hop 50.1.1.2 (if reachable through FIB).
•Packets entering an interface with source address 30.2.1.x are forwarded using traditional forwarding lookup.
•Packets entering an interface with source address 30.2.x.x but not in 30.2.1.x are forwarded to nexthop 40.1.1.2 (if reachable through FIB).
•All other packets entering an interface are permitted by ACE 25 and forwarded by using a traditional forwarding lookup.
•ACE 25 ensures that all packets not matching this ACL-based forwarding ACL are forwarded and does not get dropped due to an implicit deny ACE that is installed after ACE 25 by the software.
Additional References
The following sections provide references related to Implementing Access Lists and Prefix Lists on Cisco IOS XR software.
Related Documents
Related Topic
|
Document Title
|
Access list commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples
|
Access List Commands on Cisco IOS XR Software, Release 3.4.0
|
Prefix list commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples
|
Prefix List Commands on Cisco IOS XR Software, Release 3.4.0
|
Terminal services commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples
|
Terminal Services Commands on Cisco IOS XR Software, Release 3.4.0
|
Packet forwarding infrastructure commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples
|
Packet Forwarding Infrastructure Commands on Cisco IOS XR Software, Release 3.4.0
|
Standards
Standards
|
Title
|
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
|
—
|
MIBs
RFCs
RFCs
|
Title
|
No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.
|
—
|
Technical Assistance
Description
|
Link
|
The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.
|
http://www.cisco.com/techsupport
|
