IP Routing: BGP Configuration Guide, Cisco IOS Release 15M&T
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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.
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.
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}
mvpnvrfvrf-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
“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
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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.
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.
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