Configuring Bgp Community Filtering - Cisco Catalyst 3750-E Software Configuration Manual
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Also See for Catalyst 3750-E:
- Getting started manual (27 pages) ,
- Product support bulletin (6 pages) ,
- Configuration handbook (359 pages)
Table of Contents
Configuring BGP
sequence number command; to reenable automatic generation, use the ip prefix-list sequence number
command. To clear the hit-count table of prefix list entries, use the clear ip prefix-list privileged EXEC
command.
Configuring BGP Community Filtering
One way that BGP controls the distribution of routing information based on the value of the
COMMUNITIES attribute. The attribute is a way to groups destinations into communities and to apply
routing decisions based on the communities. This method simplifies configuration of a BGP speaker to
control distribution of routing information.
A community is a group of destinations that share some common attribute. Each destination can belong
to multiple communities. AS administrators can define to which communities a destination belongs. By
default, all destinations belong to the general Internet community. The community is identified by the
COMMUNITIES attribute, an optional, transitive, global attribute in the numerical range from
1 to 4294967200. These are some predefined, well-known communities:
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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
Catalyst 3750-E and 3560-E Switch Software Configuration Guide
40-58
internet—Advertise this route to the Internet community. All routers belong to it.
no-export—Do not advertise this route to EBGP peers.
no-advertise—Do not advertise this route to any peer (internal or external).
local-as—Do not advertise this route to peers outside the local autonomous system.
40-94.
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
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identifies one or more permit or deny groups of communities.
The community-number is the number configured by a set
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community route-map configuration command.
Enter BGP router configuration mode.
Specify that the COMMUNITIES attribute be sent to the neighbor at
this IP address.
Chapter 40
Configuring IP Unicast Routing
"Using Route Maps to
OL-9775-08
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