ip community-list

---

Defines a community based access list.

Syntax: [no] ip community-list list-name [description description] {permit|deny} [community-number]

list-name	Name of this ip community list. Names may be up to 256 characters and may consist of any alpha-numeric characters, the underscore (_), and the hyphen (-). Case is significant.
description	Specifies an identifying text description of up to 255 characters to be associated with this community-list.
permit	Permits access for matching condition.
deny	Denies access for matching condition.
community-number	Valid values for community number include: Integer from 1 to 4294967295. You can define a single number or a series of numbers separated by a space. no-export - Do not advertise this route outside a BGP confederation boundary. no-advertise - Do not advertise this route to any peers. local-as - Do not advertise this route to external peers.

Description: Access lists are filters that enable you to restrict the routing information a router learns or advertises to and from a neighbor.

Multiple BGP peers or route maps can reference a single access list. You can apply access lists to both inbound route updates and outbound route updates. Each route update is passed through the access-list. BGP applies each rule in the access list in the order it appears in the list. When a route matches any rule, the decision to permit the route through the filter or deny it is made, and no further rules are processed.

NOTE By default, an access list denies the route.

Communities are groups of destinations that share the community attribute. The ip community-list command enables you to define access lists to control routing decisions based on the community attribute. This simplifies the task of configuring a BGP speaker to control the distribution of routing information.

Use the set community command to configure the communities attribute.

Use the ip community-list command to create a community based access list. Add entries to the access list by repeating the command for different community values.

Use the no ip community-list command to delete a community-based access list.

Factory Default: If you permit a value for the community number, the community list defaults to an implicit deny for all other values.

Command Mode: Configuration.

Example 1: In the following example, the ip community-list commands create a community-list named 13 that specifies a description of Chi-Gov to Bost-Gov and permits routing updates from communities numbered 71 - 73, and rejects all other routes:

router(config)#ip community-list 13 description Chi-GovToBost-Gov router(config)#ip community-list 13 permit 71 router(config)#ip community-list 13 permit 72 router(config)#ip community-list 13 permit 73 router(config)#ip community-list 13 deny any

Like other types of access lists, ip community lists are applied to route updates using route maps.

Example 2: In the following example,

• The route-map command is used to create a route map named community 108.
  
  
• The match community command specifies that only routes that match criteria defined in community access list 13 (see example 1 above) are accepted.
  
  
• The set community command specifies that any routes that match the criteria defined in community access list 13 have the community attribute set to 108:
  
  

router(config)#route-map community108 10 permit router(config-route-map)#match community 13 router(config-route-map)#set community 108

Related Commands: access-list
ip access-list
match community
permit
route-map
set community
show access-lists
show ip community-list
neighbor distribute-list
neighbor filter-list
neighbor send-community

Copyright © 2004 Avici Systems Inc.
Avici® and TSR® is a registered trademark of Avici Systems Inc.
IPriori™, Composite Links™, SSR™, QSR, and NSR® are trademarks of Avici Systems Inc.

   Source File Name: Routing_Pol.fm
    HTML File Name: Routing_Pol10.html
    Last Updated: 05/10/04 at 16:38:37

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