BigIron RX Series Configuration Guide 79753-1001810-01Filtering 26The deny | permit parameter specifies the action the software takes if a route’s community listmatches a match statement in this ACL. To configure the community-list match statements in aroute map, use the match community command. Refer to “Matching based on community ACL” onpage 802The parameter specifies the community type or community number. Thisparameter can have the following values:• : – A specific community number• internet – The Internet community• no-export – The community of sub-ASs within a confederation. Routes with this communitycan be exported to other sub-ASs within the same confederation but cannot be exportedoutside the confederation to other ASs or otherwise sent to EBGP neighbors.• local-as – The local sub-AS within the confederation. Routes with this community can beadvertised only within the local subAS.• no-advertise – Routes with this community cannot be advertised to any other BGP4 routers atall.The parameter specifies a regular expression for matching on communitynames. For information about regular expression syntax, refer to “Using regular expressions” onpage 794. You can specify a regular expression only in an extended community ACL.To use a community-list filter, use route maps with the match community parameter.Defining and applying IP prefix listsAn IP prefix list specifies a list of networks. When you apply an IP prefix list to a neighbor, the devicesends or receives only a route whose destination is in the IP prefix list. The software interprets theprefix lists in order, beginning with the lowest sequence number.To configure an IP prefix list and apply it to a neighbor, enter commands such as the following.BigIron RX(config)# ip prefix-list Routesfor20 permit 20.20.0.0/24BigIron RX(config)# router bgpBigIron RX(config-bgp)# neighbor 10.10.10.1 prefix-list Routesfor20 outThese commands configure an IP prefix list named Routesfor20, which permits routes to network20.20.0.0/24. The neighbor command configures the device to use IP prefix list Routesfor20 todetermine which routes to send to neighbor 10.10.10.1. The device sends routes that go to20.20.x.x to neighbor 10.10.10.1 because the IP prefix list explicitly permits these routes to be sentto the neighbor.Syntax: ip prefix-list [seq ] [description ] deny | permit/ [ge ] [le ]The parameter specifies the prefix list name. You use this name when applying the prefixlist to a neighbor.The description parameter is a text string describing the prefix list.The seq parameter is optional and specifies the IP prefix list’s sequence number. Ifyou do not specify a sequence number, the software numbers them in increments of 5, beginningwith prefix list entry 5. The software interprets the prefix list entries in numerical order, beginningwith the lowest sequence number.The deny | permit parameter specifies the action the software takes if a neighbor’s route is in thisprefix list.
