Security Configuration Guide: Access Control Lists, Cisco IOS XE Release 3S
IPv6 ACL Chaining with a Common ACL
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IPv6 ACL Chaining with a Common ACL

IPv6 ACL Chaining with a Common ACL

ACL Chaining, also known as Multi-Access Control List (ACL), allows you to split ACLs. This document describes how with the IPv6 ACL Chaining Support feature, you can explicitly split ACLs into common and user-specific ACLs and bind both ACLs to a target for traffic filtering on a device. In this way, the common ACLs in Ternary Content Addressable Memory (TCAM) are shared by multiple targets, thereby reducing the resource usage.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Information About IPv6 ACL Chaining with a Common ACL

ACL Chaining Overview

The packet filter process supports only a single Access control list (ACL) to be applied per direction and per protocol on an interface. This leads to manageability and scalability issues if there are common ACL entries needed on many interfaces. Duplicate Access control entries (ACEs) are configured for all those interfaces, and any modification to the common ACEs needs to be performed for all ACLs.

A typical ACL on the edge box for an Internet Service Provider (ISP) has two sets of ACEs:
  • Common ISP specific ACEs
  • Customer/interface specific ACEs

The purpose of these address blocks is to deny access to ISP's protected infrastructure networks and anti-spoofing protection by allowing only customer source address blocks. This results in configuring unique ACL per interface and most of the ACEs being common across all ACLs on a device. ACL provisioning and modification is very cumbersome, hence, any changes to the ACE impacts every target.

IPv6 ACL Chaining with a Common ACL

With IPv6 ACL Chaining, you can configure a traffic filter with the following:

  • Common ACL
  • Specific ACL
  • Common and Specific ACL

Each Access control list (ACL) is matched in a sequence. For example, if you have specified both the ACLs - a common and a specific ACL, the packet is first matched against the common ACL; if a match is not found, it is then matched against the specific ACL.


Note


Any IPv6 ACL may be configured on a traffic filter as a common or specific ACL. However, the same ACL cannot be specified on the same traffic filter as both common and specific.

How to Configure IPv6 ACL Chaining with a Common ACL

Before You Begin
IPv6 ACL chaining is configured on an interface using an extension of the existing IPv6 traffic-filter command: ipv6 traffic-filter [common common-acl] [specific-acl] [ in | out]

Note


You may choose to configure either of the following:
  • Only a common ACL. For example: ipv6 traffic-filter common common-acl
  • Only a specific ACL. For example: ipv6 traffic-filter common-acl
  • Both ACLs. For example: ipv6 traffic-filter common common-acl specific-acl

The ipv6 traffic-filter command is not additive. When you use the command, it replaces earlier instances of the command. For example, the command sequence: ipv6 traffic-filter [common common-acl] [specific-acl] in ipv6 traffic-filter [specific-acl] in binds a common ACL to the traffic filter, removes the common ACL and then binds a specific ACL.

Configuring the IPv6 ACL to an Interface

Perform this task to configure the interface to accept a common access control list (ACL) along with an interface-specific ACL:

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface type number}

    4.    ipv6 traffic filter {common-access-list-name {in | out}}

    5.    end


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example:
    Device> enable
     

    Enables privileged EXEC mode. Enter your password if prompted.

     
    Step 2 configure terminal


    Example:
    Device# configure terminal
     

    Enters global configuration mode.

     
    Step 3 interface type number}


    Example:
    Device(config)# interface gigabitethernet 0/0/0
     

    Specifies the interface type and number, and enters interface configuration mode.

     
    Step 4 ipv6 traffic filter {common-access-list-name {in | out}}


    Example:
    Device(config)# ipv6 traffic-filter outbound out
     

    Applies the specified IPv6 access list to the interface specified in the previous step.

     
    Step 5 end


    Example:
    Device(config-if)# end
     

    (Optional) Exits the configuration mode and returns to privileged EXEC mode.

     

    Configuration Examples for IPv6 ACL Chaining with a Common ACL

    You may configure the following combinations in no particular order:

    • A common ACL, for example: ipv6 traffic-filter common common-acl in
    • A specific ACL, for example: ipv6 traffic-filter specific-acl in
    • Both ACLs, for example: ipv6 traffic-filter common common-acl specific-acl in

    Example: Configuring an Interface to Accept a Common ACL

    This example shows how to replace an access control list (ACL) configured on the interface without explicitly deleting the ACL:

    interface gigabitethernet 0/0/0
    ipv6 access-group common  C_acl ACL1 in
    end
    replace interface acl ACL1 by ACL2
    interface gigabitethernet 0/0/0
    ipv6 access-group common  C_acl ACL2 in
    end
    
    

    This example shows how to delete a common ACL from an interface. A common ACL cannot be replaced on interfaces without deleting it explicitly from the interface.

    interface gigabitethernet 0/0/0
    ipv6 access-group common  C_acl1 ACL1 in
    end
    change the common acl to C_acl2
    interface gigabitethernet 0/0/0
    no ipv6 access-group common  C_acl1  ACL1 in
    end
    interface gigabitethernet 0/0/0
    ipv6 access-group common  C_acl2  ACL1 in
    end
    
    

    Note


    When reconfiguring a common ACL, you must ensure that no other interface on the line card is attached to the common ACL.

    Note


    If both common ACL and interface ACL are attached to an interface and only one of the above is reconfigured on the interface, then the other is removed automatically.

    This example shows how to remove the interface ACL:

    interface gigabitethernet 0/0/0
    ipv6 access-group common C_acl1 ACL1 in
    end
    
    

    Additional References for IPv6 ACL Chaining with a Common ACL

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    Feature Information for IPv6 ACL Chaining with a Common ACL

    The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

    Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

    Table 1 Feature Information for IPv6 ACL Chaining with a Common ACL

    Feature Name

    Releases

    Feature Information

    IPv6 ACL Chaining with a Common ACL

    Cisco IOS XE Release 3.11S

    The ACL Chaining feature, also known as Multi-ACLs, allows you to explicitly split IPv6 traffic filter access control lists (ACLs) into common and per-session ACLs. In this way, the common access control entries (ACEs) that are used reduces resource usage of each ACL entry per session in the Ternary Content Addressable Memory (TCAM).

    The following commands were introduced or modified: ip access-group common.