Setting The Community Attribute; Filtering Via A Bgp Community; Bgp Extended Communities; Configuring A Bgp Extended Community (Route Target) - Cisco ASR 5500 Administration Manual

BGP Communities and Extended Communities

Setting the Community Attribute

You set the BGP community attribute via a set community command in a route map.
config
context context_name
route-map map_name { deny | permit } sequence_number
set community [additive]{ internet | local-AS | no-advertise | no-export | none | value
AS-community_number AS-community_number AS-community_number ...}
{ internet | local-AS | no-advertise | no-export | none | value AS-community_number
AS-community_number AS-community_number ... }
{ internet | local-AS | no-advertise | no-export | none | value AS-community_number
AS-community_number AS-community_number ... }
The additive option allows you to enter multiple destinations and AS community numbers. For additional
information, see the Command Line Interface Reference.

Filtering via a BGP Community

To filter routes based on a BGP community, you configure a match clause in a route map. The command
sequence follows below.
config
context context_name
route-map map_name { deny | permit } sequence_number
match community { named named_list | standard identifier }

BGP Extended Communities

Configuring a BGP Extended Community (Route Target)

A BGP extended community defines a route target. MPLS VPNs use a 64-bit Extended Community attribute
called a Route Target (RT). An RT enables distribution of reachability information to the correct information
table.
You configure a BGP extended community via a Context Configuration mode command.
config
context context_name
ip extcommunity-list { named named_list | standard identifier } { deny | permit } rt rt_number
rt_number rt_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.
Multiple extended community-list entries can be attached to an extended community-list by adding multiple
permit or deny clauses for various extended community strings. Up to 64 extended community-lists can be
configured in a context.
ASR 5500 System Administration Guide, StarOS Release 19
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Routing