This format allows you to easily classify community names. For example, a common convention used in community naming is to
congure the rst string as the local AS and the second string as the unique community within that AS. Using this convention,
communities 1:10, 1:20, and 1:30 can be easily identied as member communities of AS 1.
The device provides the following methods for ltering on community information.
• Community lters
• Community list ACLs
NOTE
The device cannot actively support community lters and community list ACLs at the same time. Use one method or the other
but do not mix methods.
NOTE
Once you dene a lter or ACL, the default action for communities that do not match a lter or ACL is deny . To change the
default action to permit , congure the last lter or ACL entry as permit any any .
Community lters or ACLs can be referred to by match clauses in a route map.
Dening a community ACL
To
congure community ACL 1, enter a command such as the following. This command congures a community ACL that permits
routes that contain community 123:2.
device(config)# ip community-list 1 permit 123:2
Syntax: no ip community-list standard string [ seq seq-value ] deny | permit community-num
The string parameter species the ACL name. (If you enter a number, the CLI interprets the number as a text string.)
The standard parameter species whether you are conguring a standard community ACL.
The seq seq-value parameter is optional and species the sequence number for the community list. You can congure up to 199 entries
in a community list. If you do not specify a sequence number, the software numbers the entries in increments of 5, beginning with
number 5. The software interprets the entries in a community list in numerical order, beginning with the lowest sequence number.
The deny and permit parameters specify the action the software takes if a route community list matches a match clause in this ACL. To
congure the community-list match clauses in a route map, use the match community command.
The community-num parameter species the community type or community number. This parameter can have the following values:
• num:num - A specic community number
• internet - The Internet community
• no-export - The community of sub-autonomous systems within a confederation. Routes with this community can be exported
to other sub-autonomous systems within the same confederation but cannot be exported outside the confederation to other
autonomous systems or otherwise sent to EBGP neighbors.
• local-as - The local sub-AS within the confederation. Routes with this community can be advertised only within the local subAS.
• no-advertise - Routes with this community cannot be advertised to any other BGP4 devices at all.
The regular-expression parameter species a regular expression for matching on community names.
To use a community-list lter, use route maps with the match community parameter.
Filtering
FastIron Ethernet Switch Layer 3 Routing
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