Multicast VPN BGP Dampening

A single receiver in a specific multicast group or a group of receivers that are going up and down frequently and interested in a specific multicast group activates the Multicast VPN BGP Dampening feature to dampen type 7 routes (C-multicast route Join/Prune) within the core using BGP signaling. The feature reduces the churn caused by customer-side join/prune requests to avoid unnecessary BGP MVPN type 6/7 C-route control information.

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.

Prerequisites for Multicast VPN BGP Dampening

  • You understand the concepts in the “BGP Route Dampening” module of the IP Routing: BGP Configuration Guide.

Information About Multicast VPN BGP Dampening

Overview of Multicast VPN BGP Dampening

BGP Route Dampening

Route dampening is a BGP feature designed to minimize the propagation of flapping routes across an internetwork. A route is considered to be flapping when its availability alternates repeatedly. Cisco devices that are running BGP contain a mechanism designed to “dampen” the destabilizing effect of flapping routes. When a Cisco device running BGP detects a flapping route, it automatically dampens that route.

The figure below shows illustrates the Multicast VPN BGP dampening mechanism.

Multicast VPN BGP Dampening

Figure 1. Multicast VPN BGP Dampening

A single receiver in a multicast group or a group of receivers that are flapping frequently and interested in a specific multicast group actrivates multicast VPN (MVPN) BGP dampening. MVPN BGP dampening dampens the type 7 multicast routes (customer-multicast, or “C-multicast,” route join/prune) within the core using BGP signaling.

When MVPN BGP dampening is not enabled, the source sends data even though the receiver may be down. When the receiver is down, there is no periodic 60-second C-PIM join towards the provider edge (PE) device causing the PIM to timeout on the PE side after the default period (three minutes). The MVPN manager sends a prune message to BGP, which is a type 7 route (C-multicast route withdraw).

When the receiver is up, it sends a new (S,G) join request to the customer edge (CE) device. The C-PIM join is received by the PE device and a new type 7 C-multicast update is sent by BGP to the auto-discovered MVPN peers. The upstream multicast peer converts the BGP type 7 update to a PIM join to the source, and the source sends the data traffic that the receiver should receive via the downstream PE using the MDT tunnel. If the receiver goes up and down frequently, the source side PIM receives join/prune messages frequently and can cause the source to respond accordingly.

When MVPN BGP dampening is enabled, the general dampening mechanism in BGP will be applied to MVPN VRF instances. Join/Prune messages from the CE side are sent from an MVPN manager as updates/withdraw to the MVPN PE device. The MVPN manager on PE devices send join/prune messages to the customer side for Reverse Path Forwarding (RPF) and upstream multihop (UMH) nexthop changes.

How to Configure Multicast VPN BGP Dampening

Configuring Multicast VPN BGP Dampening

Perform this task to enable and configure multicast VPN BGP dampening.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    router bgp as-number

    4.    address-family [ipv4 | ipv6] mvpn vrf vrf-name

    5.    bgp dampening [half-life reuse suppress max-suppress-time]

    6.    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 router bgp as-number


    Example:
    Device(config)# router bgp 45000
     

    Enters router configuration mode and creates a BGP routing process.

     
    Step 4 address-family [ipv4 | ipv6] mvpn vrf vrf-name


    Example:
    Device(config-router)# address-family ipv4 mvpn vrf blue
     
    Specifies the address family and enters address family configuration mode.

    • Use the ipv4 keyword to enable IPv4 multicast C-route exchange.

    • Use the ipv6 keyword to enable IPv6 multicast C-route exchange.

    Note   

    The vrf keyword and vrf-name argument must be specified at this point to enable multicast VPN BGP dampening in the next step.

     
    Step 5 bgp dampening [half-life reuse suppress max-suppress-time]


    Example:
    Device(config-router-af)# bgp dampening 30 1500 10000 120
     

    Enables BGP route dampening and changes the default values of route dampening factors. The half-life, reuse, suppress, and max-suppress-time arguments are all position dependent; if one argument is entered, then all the arguments must be entered.

    Note   

    Repeat steps 4 and 5 to enable multicast VPN BGP dampening on alternative VRFs.

     
    Step 6 end


    Example:
    Device(config-router-af)# end
     

    Exits address family configuration mode and enters privileged EXEC mode.

     

    Monitoring and Maintaining Multicast VPN BGP Dampening

    Perform the steps in this task as required to monitor and maintain multicast VPN BGP dampening.

    SUMMARY STEPS

      1.    enable

      2.    show bgp {ipv4 | ipv6} mvpn {all | rd route-distinguisher | vpn vrf-name} [dampening {dampened-paths | flap-statistics [filter-list access-list-number | quote-regexp regexp | regexp regexp]}]

      3.    clear ip bgp {ipv4 | ipv6} mvpn vrf vrf-name {dampening | flap-statistics}


    DETAILED STEPS
      Step 1   enable

      Enables privileged EXEC mode. Enter your password if prompted.



      Example:
      Device> enable
      Step 2   show bgp {ipv4 | ipv6} mvpn {all | rd route-distinguisher | vpn vrf-name} [dampening {dampened-paths | flap-statistics [filter-list access-list-number | quote-regexp regexp | regexp regexp]}]
      Use this command to monitor multicast VPN BGP dampening.

      • The dampened-path keyword displays information about BGP dampened routes.

      • The parameters keyword displays detailed BGP dampening information.

      • The flap-statistics keyword displays information on BGP flap statistics.



      Example:
      Device# show bgp ipv4 mvpn vrf blue route-type 7 111.111.111.111:11111 55 202.100.0.6 232.1.1.1

BGP routing table entry for [7][111.111.111.111:11111][55][202.100.0.6/32][232.1.1.1/32]/22, version 17
Paths: (1 available, no best path)
Flag: 0x820
  Not advertised to any peer
  Refresh Epoch 1
  Local, (suppressed due to dampening)
    0.0.0.0 from 0.0.0.0 (205.3.0.3)
      Origin incomplete, localpref 100, weight 32768, valid, sourced, local
      Extended Community: RT:205.1.0.1:1
      Dampinfo: penalty 3472, flapped 4 times in 00:04:42, reuse in 00:00:23  
      rx pathid: 0, tx pathid: 0
      Step 3   clear ip bgp {ipv4 | ipv6} mvpn vrf vrf-name {dampening | flap-statistics}
      Use this command to clear the accumulated penalty for routes that are received on a router that has multicast VPN BGP dampening enabled.

      • The dampening keyword clears multicast VPN BGP dampening information.

      • The flap-statistic keyword clears multicast VPN BGP dampening flap statistics.



      Example:
      Device# clear ip bgp ipv4 mvpn vrf blue dampening

      Configuration Examples for Multicast VPN BGP Dampening

      Example: Configuring Multicast VPN BGP Dampening

      The following example shows multicast VPN BGP dampening is applied to the VRFs named blue and red, but not to the VRF named green: 

      address-family ipv4 mvpn vrf blue
 bgp dampening

address-family ipv4 mvpn vrf red
 bgp dampening

address-family ipv4 mvpn vrf green
 no bgp dampening

      Additional References for Multicast VPN BGP Dampening

      Related Documents

      Related Topic

      Document Title

      Cisco IOS commands

      Cisco IOS Master Command List, All Releases

      BGP commands

      Cisco IOS IP Routing: BGP Command Reference

      BGP route dampening

      “BGP Route Dampening” section of the “Configuring Internal BGP Features” module in the IP Routing: BGP Configuration Guide

      Standards and RFCs

      Standard/RFC

      Title

      RFC 2439

      BGP Route Flap Damping

      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 Multicast VPN BGP Dampening

      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 Multicast VPN BGP Dampening

      Feature Name

      Releases

      Feature Information

      Multicast VPN BGP Dampening

      Cisco IOS XE Release 3.8S

      A single receiver in a specific multicast group or a group of receivers that are going up and down frequently and interested in a specific multicast group will cause the Multicast VPN BGP Dampening feature to dampen type 7 routes (C-multicast route join/prune) within the core using BGP signaling.

      The following commands were introduced or modified: address-family mvpn, clear ip bgp mvpn, show bgp mvpn, and show ip bgp ipv4.