Cisco Catalyst 3550 series Software Configuration Manual page 735

Chapter 31 Configuring IP Unicast Routing
Based on the community, you can control which routing information to accept, prefer, or distribute to
other neighbors. A BGP speaker can set, append, or modify the community of a route when learning,
advertising, or redistributing routes. When routes are aggregated, the resulting aggregate has a
COMMUNITIES attribute that contains all communities from all the initial routes.
You can use community lists to create groups of communities to use in a match clause of a route map.
As with an access list, a series of community lists can be created. Statements are checked until a match
is found. As soon as one statement is satisfied, the test is concluded.
To set the COMMUNITIES attribute and match clauses based on communities, see the match
community-list and set community route-map configuration commands in the
Redistribute Routing Information" section on page
By default, no COMMUNITIES attribute is sent to a neighbor. You can specify that the COMMUNITIES
attribute be sent to the neighbor at an IP address by using the neighbor send-community router
configuration command.
Beginning in privileged EXEC mode, follow these steps to create and to apply a community list:
Command
Step 1
configure terminal
Step 2
ip community-list community-list-number
{permit | deny} community-number
Step 3
router bgp autonomous-system
Step 4
neighbor {ip-address | peer-group name}
send-community
Step 5
set comm-list list-num delete
Step 6
exit
Step 7
ip bgp-community new-format
Step 8
end
Step 9 show ip bgp community
Step 10 copy running-config startup-config
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Purpose
Enter global configuration mode.
Create a community list and assign it a number.
The community-list-number is an integer from 1 to 99 that
•
identifies one or more permit or deny groups of communities.
The community-number is the number configured by a set
•
community route-map configuration command.
Enter BGP router configuration mode.
Specify that the COMMUNITIES attribute be sent to the neighbor at
this IP address.
(Optional) Remove communities from the community attribute of an
inbound or outbound update that match a standard or extended
community list specified by a route map.
Return to global configuration mode.
(Optional) Display and parse BGP communities in the format AA:NN.
A BGP community appears in a 2-part format two bytes long. The Cisco
default community format is in the format NNAA. In the most recent
RFC for BGP, a community takes the form AA:NN, where the first part
is the AS number and the second part is a 2-byte number.
Return to privileged EXEC mode.
Verify the configuration.
(Optional) Save your entries in the configuration file.
Catalyst 3550 Multilayer Switch Software Configuration Guide
Configuring BGP
"Using Route Maps to
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