Contents

Enhanced IPv6 Neighbor Discovery Cache Management

The IPv6 highly scalable neighbor discovery feature optimizes IPv6 neighbor discovery by providing Neighbor Discovery (ND) cache autorefresh, unsolicited NA gleaning, and neighbor unreachability detection (NUD) exponential retransmit. This feature makes ND more robust in a large-scale deployment

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 Enhanced IPv6 Neighbor Discovery Cache Management

Enhanced IPv6 Neighbor Discovery Cache Management Overview

Neighbor discovery (ND) protocol enforces neighbor unreachability detection (NUD), which can detect failing nodes or routers and changes, to link-layer addresses. NUD is used to maintain reachability information for all paths between hosts and neighboring nodes, including host-to-host, host-to-router, and router-to-host communication.

The neighbor cache maintains mapping information about the IPv6 link-local or global address to the link-layer address. The neighbor cache also maintains the neighbor's reachability state, which is updated using NUD. Neighbors can be in one of the following five possible states:

  • DELAY—Neighbor is pending re-resolution, and traffic might flow to this neighbor.
  • INCOMPLETE—Address resolution is in progress, and the link-layer address is not yet known.
  • PROBE—Neighbor re-resolution is in progress, and traffic might flow to this neighbor.
  • REACHABLE—Neighbor is known to be reachable within the last reachable time interval.
  • STALE—Neighbor requires re-resolution, and traffic may flow to this neighbor.

Use the ipv6 nd na glean command to configure ND to glean an entry from an unsolicited neighbor advertisement (NA).

Use the ipv6 nd nud retry command to configure ND to maintain an ND cache entry for a neighbor during network disruption.

Use the ipv6 nd cache expire refresh command to configure the neighbor to maintain an ND cache entry, when no traffic is sent to the neighbor.

How to Configure Enhanced IPv6 Neighbor Discovery Cache Management

Customizing the Parameters for IPv6 Neighbor Discovery

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface type number

    4.    ipv6 nd nud retry base interval max-attempts [final-wait-time]

    5.    ipv6 nd cache expire expire-time-in-seconds [refresh]

    6.    ipv6 nd na glean

    7.    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 Ethernet 1/0
     

    Specifies an interface type and number, and places the device in interface configuration mode.

     
    Step 4 ipv6 nd nud retry base interval max-attempts [final-wait-time]


    Example:
    Device(config-if)# ipv6 nd nud retry 1 1000 3 1000
     

    Configures the number of times neighbor unreachability detection (NUD) resends neighbor solicitations (NS) before the final wait time on the last probe and the interval between NS during NUD.

    When a device runs NUD to resolve the ND entry for a neighbor, it sends three NS packets 1 second apart. In certain situations (for example, spanning-tree events, high traffic, the end host being reloaded), three NS packets sent at an interval of 1 second may not be sufficient. To help maintain the neighbor cache in such situations, use the ipv6 nd nud retry command to configure exponential timers for NS retransmits.

    The retransmit probe time is calculated by tm^n (where, t = interval, m = base, and n = current attempt). Therefore, ipv6 nd nud retry 3 1000 5 command will produce retransmit intervals of 1,3,9,27,81 seconds. If the final-wait-time is not configured, the entry remains for 243 seconds before it is deleted.

    • The range for base is from 1 to 3.
    • The range for interval is from 1000 to 32000 milliseconds.
    • The range for max-attempts is from 1 to 128.
    • The range for final-wait-time is from 1000 to 32000 milliseconds.
     
    Step 5 ipv6 nd cache expire expire-time-in-seconds [refresh]


    Example:
    Device(config-if)# ipv6 nd cache expire 7200
     

    Configures the length of time before an IPv6 neighbor discovery cache entry expires. The range is from 1 to 65536 seconds.

    By default, an ND cache entry is expired and deleted if it remains in the STALE state for 14,400 seconds, or 4 hours. The ipv6 nd cache expire command allows the user to vary the expiry time and to trigger autorefresh of an expired entry before the entry is deleted.

    When the refresh keyword is used, an ND cache entry is autorefreshed. The entry moves into the DELAY state and the NUD process occurs, in which the entry transitions from the DELAY state to the PROBE state after 5 seconds. When the entry reaches the PROBE state, a neighbor solicitation (NS) is sent and then retransmitted as per the configuration.

    When you configure the expiry duration, the device will probe the neighbor on entry expiration, that is, the neighbor discovery enters into the probe state and sends a neighbor solicitation to the neighbor. If the neighbor responds, the ND cache entry reverts to the reachable state. If the neighbor does not respond, the cache entry is deleted.

    This maintains an entry in the ND cache until the neighbor exists and is reachable, even if no traffic is sent to the neighbor.

     
    Step 6 ipv6 nd na glean


    Example:
    Device(config-if)# ipv6 nd na glean
     

    Configures ND to glean an entry from an unsolicited neighbor advertisement (NA).

    The IPv6 ND ignores an unsolicited NA packet if it does not have a cache entry for the neighbor that is sending the NA. If the ND is configured on an interface to glean an entry from an unsolicited NA, the neighbor discovery protocol creates neighbor discovery cache entries based on unsolicited NA packets sent from the previously unknown neighbors on that interface. This allows the device to populate its ND cache with an entry for a neighbor in advance of any data traffic exchange with the neighbor.

     
    Step 7end

    Example:
    Device(config-if)# end
     

    Exits interface configuration mode and returns to privileged EXEC mode.

     

    Configuration Examples for Enhanced IPv6 Neighbor Discovery Cache Management

    Example: Customizing the Parameters for IPv6 Neighbor Discovery

    In the following example, IPv6 ND NA gleaning is enabled and the IPv6 ND cache expiry is set to 7200 seconds (2 hours): 

    interface Port-channel189
 no ip address
 ipv6 address FC07::789:1:0:0:3/64
 ipv6 nd nud retry 1 1000 3 1000
 ipv6 nd na glean
 ipv6 nd cache expire 7200
 no ipv6 redirects

    Additional References

    Related Documents

    Related Topic

    Document Title

    IPv6 addressing and connectivity

    IPv6 Configuration Guide

    Cisco IOS commands

    Cisco IOS Master Commands 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

    MIBs

    MIB

    MIBs Link

    No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

    To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

    http:/​/​www.cisco.com/​go/​mibs

    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 Enhanced IPv6 Neighbor Discovery Cache Management

    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 Enhanced IPv6 Neighbor Discovery Cache Management

    Feature Name

    Releases

    Feature Information

    Enhanced IPv6 Neighbor Discovery Cache Management

    12.2(33)SXI7

    Cisco IOS Release 15.2(1)E

    The IPv6 highly scalable neighbor discovery feature optimizes IPv6 neighbor discovery by providing ND cache autorefresh, unsolicited NA gleaning, and NUD exponential retransmit.

    The following commands were introduced or modified: ipv6 nd cache expire, ipv6 nd na glean, ipv6 nd nud retry.
    Enhanced IPv6 Neighbor Discovery Cache Management

    Enhanced IPv6 Neighbor Discovery Cache Management

    The IPv6 highly scalable neighbor discovery feature optimizes IPv6 neighbor discovery by providing Neighbor Discovery (ND) cache autorefresh, unsolicited NA gleaning, and neighbor unreachability detection (NUD) exponential retransmit. This feature makes ND more robust in a large-scale deployment

    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 Enhanced IPv6 Neighbor Discovery Cache Management

    Enhanced IPv6 Neighbor Discovery Cache Management Overview

    Neighbor discovery (ND) protocol enforces neighbor unreachability detection (NUD), which can detect failing nodes or routers and changes, to link-layer addresses. NUD is used to maintain reachability information for all paths between hosts and neighboring nodes, including host-to-host, host-to-router, and router-to-host communication.

    The neighbor cache maintains mapping information about the IPv6 link-local or global address to the link-layer address. The neighbor cache also maintains the neighbor's reachability state, which is updated using NUD. Neighbors can be in one of the following five possible states:

    • DELAY—Neighbor is pending re-resolution, and traffic might flow to this neighbor.
    • INCOMPLETE—Address resolution is in progress, and the link-layer address is not yet known.
    • PROBE—Neighbor re-resolution is in progress, and traffic might flow to this neighbor.
    • REACHABLE—Neighbor is known to be reachable within the last reachable time interval.
    • STALE—Neighbor requires re-resolution, and traffic may flow to this neighbor.

    Use the ipv6 nd na glean command to configure ND to glean an entry from an unsolicited neighbor advertisement (NA).

    Use the ipv6 nd nud retry command to configure ND to maintain an ND cache entry for a neighbor during network disruption.

    Use the ipv6 nd cache expire refresh command to configure the neighbor to maintain an ND cache entry, when no traffic is sent to the neighbor.

    How to Configure Enhanced IPv6 Neighbor Discovery Cache Management

    Customizing the Parameters for IPv6 Neighbor Discovery

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    interface type number

      4.    ipv6 nd nud retry base interval max-attempts [final-wait-time]

      5.    ipv6 nd cache expire expire-time-in-seconds [refresh]

      6.    ipv6 nd na glean

      7.    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 Ethernet 1/0
       

      Specifies an interface type and number, and places the device in interface configuration mode.

       
      Step 4 ipv6 nd nud retry base interval max-attempts [final-wait-time]


      Example:
      Device(config-if)# ipv6 nd nud retry 1 1000 3 1000
       

      Configures the number of times neighbor unreachability detection (NUD) resends neighbor solicitations (NS) before the final wait time on the last probe and the interval between NS during NUD.

      When a device runs NUD to resolve the ND entry for a neighbor, it sends three NS packets 1 second apart. In certain situations (for example, spanning-tree events, high traffic, the end host being reloaded), three NS packets sent at an interval of 1 second may not be sufficient. To help maintain the neighbor cache in such situations, use the ipv6 nd nud retry command to configure exponential timers for NS retransmits.

      The retransmit probe time is calculated by tm^n (where, t = interval, m = base, and n = current attempt). Therefore, ipv6 nd nud retry 3 1000 5 command will produce retransmit intervals of 1,3,9,27,81 seconds. If the final-wait-time is not configured, the entry remains for 243 seconds before it is deleted.

      • The range for base is from 1 to 3.
      • The range for interval is from 1000 to 32000 milliseconds.
      • The range for max-attempts is from 1 to 128.
      • The range for final-wait-time is from 1000 to 32000 milliseconds.
       
      Step 5 ipv6 nd cache expire expire-time-in-seconds [refresh]


      Example:
      Device(config-if)# ipv6 nd cache expire 7200
       

      Configures the length of time before an IPv6 neighbor discovery cache entry expires. The range is from 1 to 65536 seconds.

      By default, an ND cache entry is expired and deleted if it remains in the STALE state for 14,400 seconds, or 4 hours. The ipv6 nd cache expire command allows the user to vary the expiry time and to trigger autorefresh of an expired entry before the entry is deleted.

      When the refresh keyword is used, an ND cache entry is autorefreshed. The entry moves into the DELAY state and the NUD process occurs, in which the entry transitions from the DELAY state to the PROBE state after 5 seconds. When the entry reaches the PROBE state, a neighbor solicitation (NS) is sent and then retransmitted as per the configuration.

      When you configure the expiry duration, the device will probe the neighbor on entry expiration, that is, the neighbor discovery enters into the probe state and sends a neighbor solicitation to the neighbor. If the neighbor responds, the ND cache entry reverts to the reachable state. If the neighbor does not respond, the cache entry is deleted.

      This maintains an entry in the ND cache until the neighbor exists and is reachable, even if no traffic is sent to the neighbor.

       
      Step 6 ipv6 nd na glean


      Example:
      Device(config-if)# ipv6 nd na glean
       

      Configures ND to glean an entry from an unsolicited neighbor advertisement (NA).

      The IPv6 ND ignores an unsolicited NA packet if it does not have a cache entry for the neighbor that is sending the NA. If the ND is configured on an interface to glean an entry from an unsolicited NA, the neighbor discovery protocol creates neighbor discovery cache entries based on unsolicited NA packets sent from the previously unknown neighbors on that interface. This allows the device to populate its ND cache with an entry for a neighbor in advance of any data traffic exchange with the neighbor.

       
      Step 7end

      Example:
      Device(config-if)# end
       

      Exits interface configuration mode and returns to privileged EXEC mode.

       

      Configuration Examples for Enhanced IPv6 Neighbor Discovery Cache Management

      Example: Customizing the Parameters for IPv6 Neighbor Discovery

      In the following example, IPv6 ND NA gleaning is enabled and the IPv6 ND cache expiry is set to 7200 seconds (2 hours): 

      interface Port-channel189
 no ip address
 ipv6 address FC07::789:1:0:0:3/64
 ipv6 nd nud retry 1 1000 3 1000
 ipv6 nd na glean
 ipv6 nd cache expire 7200
 no ipv6 redirects

      Additional References

      Related Documents

      Related Topic

      Document Title

      IPv6 addressing and connectivity

      IPv6 Configuration Guide

      Cisco IOS commands

      Cisco IOS Master Commands 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

      MIBs

      MIB

      MIBs Link

      No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

      To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

      http:/​/​www.cisco.com/​go/​mibs

      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 Enhanced IPv6 Neighbor Discovery Cache Management

      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 Enhanced IPv6 Neighbor Discovery Cache Management

      Feature Name

      Releases

      Feature Information

      Enhanced IPv6 Neighbor Discovery Cache Management

      12.2(33)SXI7

      Cisco IOS Release 15.2(1)E

      The IPv6 highly scalable neighbor discovery feature optimizes IPv6 neighbor discovery by providing ND cache autorefresh, unsolicited NA gleaning, and NUD exponential retransmit.

      The following commands were introduced or modified: ipv6 nd cache expire, ipv6 nd na glean, ipv6 nd nud retry.