IPv6 Source Guard and Prefix Guard

IPv6 Source Guard and IPv6 Prefix Guard are Layer 2 snooping features that validate the source of IPv6 traffic. IPv6 Source Guard blocks any data traffic from an unknown source. For example, one that is not already populated in the binding table or previously learned through Neighbor Discovery (ND) or Dynamic Host Configuration Protocol (DHCP) gleaning. IPv6 Prefix Guard prevents home-node sourcing traffic outside of the authorized and delegated traffic.

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Information about IPv6 Source Guard and Prefix Guard

IPv6 Source Guard Overview

IPv6 source guard is an interface feature between the populated binding table and data traffic filtering. This feature enables the device to deny traffic when it is originated from an address that is not stored in the binding table. IPv6 source guard does not inspect ND or DHCP packets; rather, it works in conjunction with IPv6 neighbor discovery (ND) inspection or IPv6 address glean, both of which detect existing addresses on the link and store them into the binding table. IPv6 source guard is an interface between the populated binding table and data traffic filtering, and the binding table must be populated with IPv6 prefixes for IPv6 source guard to work.

IPv6 source guard can deny traffic from unknown sources or unallocated addresses, such as traffic from sources not assigned by a DHCP server. When traffic is denied, the IPv6 address glean feature is notified so that it can try to recover the traffic by querying the DHCP server or by using IPv6 ND. The data-glean function prevents the device and end user from getting deadlocked, whereupon a valid address fails to be stored into the binding table, there is no recovery path, and the end user is unable to connect.

The following illustration provides an overview of how IPv6 source guard works with IPv6 address glean.

Figure 1. IPv6 Source Guard and Address Glean Overview

IPv6 Prefix Guard Overview

The IPv6 Prefix Guard feature works within the IPv6 Source Guard feature, enabling the device to deny traffic originated from nontopologically correct addresses. IPv6 prefix guard is often used when IPv6 prefixes are delegated to devices (for example, home gateways) using DHCP prefix delegation. The feature discovers ranges of addresses assigned to the link and blocks any traffic sourced with an address outside this range.

To determine which prefixes should be allowed and which prefixes should be blocked, IPv6 prefix guard uses the following:

  • Prefix glean in Router Advertisements (RAs)

  • Prefix glean in DHCP prefix delegation

  • Static configuration

Whenever a prefix is to be allowed, IPv6 prefix guard downloads it to the hardware table. Whenever a packet is switched, the hardware matches the source of the packet against this table and drops the packet if no match is found.

The following figure shows a service provider (SP) scenario in which prefixes are gleaned in DHCP-PD messages.

Figure 2. Prefixes Gleaned in DHCP-PD Messages Scenario

How to Configure IPv6 Source Guard and Prefix Guard

Configuring IPv6 Source Guard

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    ipv6 source-guard policy snooping-policy

    4.    permit link-local

    5.    deny global-autoconfig

    6.    trusted

    7.    exit

    8.    show ipv6 source-guard policy [snooping-policy]


DETAILED STEPS
    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   ipv6 source-guard policy snooping-policy


    Example:
    Device(config)# ipv6 source-guard policy

    Defines an IPv6 source-guard policy name and enters source-guard policy configuration mode.

    Step 4   permit link-local


    Example:
    Device(config-source-guard)# permit link-local

    Allows hardware bridging for all data traffic sourced by a link-local address.

    Step 5   deny global-autoconfig


    Example:
    Device(config-source-guard)# deny global-autoconfig

    Denies data traffic from auto-configured global addresses.

    Step 6   trusted

    Example:
    trusted

    Step 7   exit


    Example:
    Device(config-if)# exit

    Exits source-guard policy configuration mode and places the device in privileged EXEC mode.

    Step 8   show ipv6 source-guard policy [snooping-policy]

    Displays the IPv6 source-guard policy configuration.

    Configuring IPv6 Source Guard on an Interface

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    interface type number

      4.    ipv6 source-guard attach-policy source-guard-policy

      5.    exit

      6.    show ipv6 source-guard policy source-guard-policy


    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 fastethernet 3/13
       

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

       
      Step 4ipv6 source-guard attach-policy source-guard-policy


      Example:
      Device(config-if)# ipv6 source-guard attach-policy my_source_guard_policy
       

      Applies IPv6 source guard on an interface.

       
      Step 5exit


      Example:
      Device(config-if)# exit
       

      Exits interface configuration mode and places the device in privileged EXEC mode.

       
      Step 6show ipv6 source-guard policy source-guard-policy


      Example:
      Device# show ipv6 source-guard policy policy1
       

      Displays all the interfaces on which IPv6 source guard is applied.

       

      Configuring IPv6 Prefix Guard

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    ipv6 source-guard policy snooping-policy

        4.    validate address

        5.    validate prefix

        6.    exit

        7.    show ipv6 source-guard policy [snooping-policy]


      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 3ipv6 source-guard policy snooping-policy


        Example:
        Device(config)# ipv6 source-guard policy
         

        Defines an IPv6 source-guard policy name and enters source-guard policy configuration mode.

         
        Step 4validate address


        Example:
        Device(config-source-guard)# no validate address
         

        Disables the validate address feature and enables the IPv6 prefix guard feature to be configured.

         
        Step 5validate prefix


        Example:
        Device(config-source-guard)# validate prefix
         

        Enables IPv6 source guard to perform the IPv6 prefix-guard operation.

         
        Step 6exit


        Example:
        Device(config-if)# exit
         

        Exits source-guard policy configuration mode and places the device in privileged EXEC mode.

         
        Step 7show ipv6 source-guard policy [snooping-policy]
         

        Displays the IPv6 source-guard policy configuration.

         

        Configuration Examples for IPv6 Source Guard and Prefix Guard

        Example: Configuring IPv6 Source Guard and Prefix Guard

        Device# ipv6 source-guard policy policy1

Policy guard configuration:
  validate prefix
  validate address

        Additional References for IPv6 Source Guard and Prefix Guard

        Related Documents

        Related Topic

        Document Title

        IPv6 addressing and connectivity

        IPv6 Configuration Guide

        IPv4 addressing

        IP Addressing: IPv4 Addressing Configuration Guide

        Cisco IOS commands

        Cisco IOS Master Command List, All Releases

        IPv6 commands

        Cisco IOS IPv6 Command Reference

        Cisco IOS IPv6 features

        Cisco IOS IPv6 Feature Mapping

        Standards and RFCs

        Standard/RFC

        Title

        RFCs for IPv6

        IPv6 RFCs

        Technical Assistance

        Description

        Link

        The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

        http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

        Feature Information for IPv6 Source Guard and Prefix Guard

        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 Source Guard and Prefix Guard

        Feature Name

        Releases

        Feature Information

        IPv6 Prefix Guard

        15.3(1)S

        15.2(1)E

        15.2(1)SY

        The IPv6 Prefix Guard feature enables a device to deny traffic originated from nontopologically correct addresses.

        The following commands were introduced or modified: ipv6 source-guard policy, permit link-local, show ipv6 source-guard policy, validate address, validate prefix.

        IPv6 Source Guard

        15.0(2)SE

        15.2(1)E

        15.3(1)S

        IOS XE 3.6.0E, IOS 15.2(2)E

        The IPv6 source guard feature blocks any data traffic sourced from an unknown source. For example, one that is not already populated in the binding table or previously learned through ND or DHCP gleaning.

        The following commands were introduced or modified: deny global-autoconfig, ipv6 source-guard attach-policy, ipv6 source-guard policy, permit link-local, show ipv6 source-guard policy, trusted.