Information Technology Reference
In-Depth Information
number or name, a match is found when any entry matches—that is, an OR comparison.
Example 4-10 shows two forms of community lists.
Example 4-10
Two Ways of Entering Community Lists
ip community-list 1 permit 100:1 100:2
ip community-list 2 permit 100:1
ip community-list 2 permit 100:2
With
list 1
, a match is found only when both community values of 100:1 and 100:2 are
attached to a prefix. For
list 2
, a match is found if a prefix has a community with either
100:1 or 100:2 or both. Note that the rules stated here apply only to matching community
values. They do not indicate whether a community is permitted or denied. For example, if
the community list 2 in Example 4-10 is changed to deny 100:1 and 100:2 and to permit all
other community values, a prefix with a community of 100:1 and 100:2 results in a match,
and the prefix is denied.
To announce community settings to a peer, you must configure the command
neighbor
send-community
for that peer. The result of this command is to send the peer with the
communities permitted by the local outbound policies of the best paths.
NOTE
Besides private communities, there are four well-known communities, as discussed in
Chapter 2, “Understanding BGP Building Blocks”—
internet
,
no-export
,
local-as
, and
no-
advertise
.
Community values for a prefix can be set or reset in two ways:
•
Use a
set
clause within a route map to set a community value, to add a community
value (
additive
), or to remove all community values:
set community {community-value [additive]} | none
•
Use a
set
clause within a route map to selectively remove some community values:
set comm-list community-list-number delete
This route map
set
command removes communities from the community attribute of
an inbound or outbound update. Each community that matches the given community
list is removed from the community attribute. When used with this command, each
entry of a standard community list should list only one community.
