Setting The Extended Community Attribute; Filtering Via A Bgp Extended Community; Bgp Local Preference; Icsr And Srp Groups - Cisco ASR 5500 Administration Manual

Routing

Setting the Extended Community Attribute

You set the BGP extended community attribute via a set extcommunity command in a route map.
config
context context_name
route-map map_name { deny | permit } sequence_number
rt_number specifies a Route Target as a string in AS:NN format, where AS = 2-byte AS-community
hexadecimal number and NN = 2-byte hexadecimal number (1 to 11 characters). You can add multiple route
numbers to an IP extcommunity list.

Filtering via a BGP Extended Community

To filter routes based on a BGP extended community (route target), you configure a match clause in a route
map. The command sequence follows below.
config
context context_name
route-map map_name { deny | permit }

BGP Local Preference

The BGP local preference attribute is sent by a BGP speaker only to IBGP peers. It is set in a route map via
the following command sequence:
config
context context_name
route-map map_name { deny | permit }
There is no match clause corresponding to local preference in the route-map because local-preference is
directly used in the route selection algorithm.

ICSR and SRP Groups

BGP is employed with Interchassis Session Recovery (ICSR) configurations linked via Service Redundancy
Protocol (SRP). By default an ICSR failover is triggered when all BGP peers within a context are down.
Optionally, you can configure SRP peer groups within a context. ICSR failover would then occur if all peers
within a group fail. This option is useful in deployments in which a combination of IPv4 and IPv6 peers are
spread across multiple paired VLANs, and IPv4 or IPv6 connectivity is lost by all members of a peer group.
For additional information refer to Interchassis Session Recovery in this guide and the description of the
monitor bgp, monitor diameter and monitor authentication-probe commands in the Service Redundancy
Protocol Configuration Mode Commands chapter of the Command Line Interface Reference.

Advertising BGP Routes from a Standby ICSR Chassis

An SRP Configuration mode command enables advertising BGP routes from an ICSR chassis in standby state.
This command and its keywords allow an operator to take advantage of faster network convergence accrued
set extcommunity rt rt_number rt_number rt_number ...
[no] match extcommunity { named named_list | standard identifier }
set local-preference pref_number
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