Allied Telesis x908, X8100 manual A community list, Case

BGP: Configuring Route Maps

Case 1:

awplus(config)# ip as-path access-list example deny ^$ awplus(config)# ip as-path access-list example permit 15557 awplus(config)# router bgp 100

awplus(config-router)#neighbor 192.168.200.201 filter-list example out

Case 2:

awplus(config)# ip as-path access-list example permit ^$ awplus(config)# ip as-path access-list example deny 15557 awplus(config)# route-map rmapexample deny 1

awplus(config-route-map)# match as-path example awplus(config-route-map)# route-map rmapexample permit 65535 awplus(config-route-map)# router bgp 100

awplus(config-router)#neighbor 192.168.200.201 route-map rmapexample out

Both of these configurations would cause outgoing update packets with empty AS paths to be dropped, and update packets with an AS path containing 15557 to be allowed.

But, to achieve that in the second case, the AS path list has to be configured to permit empty paths. This way, the empty path will match the AS path list, and be included into the route map's action of dropping packets that match the AS path list.

In the second case, the AS path list specifically excludes packets whose AS path contains 15557. Therefore, these packets are not dropped by the first route map entry, and are permitted by the last (permit all) route map entry.

A community list

Creating A community list is a set of entries that specify which community attribute values are included in or excluded from the list.

There are two types of community list: standard and expanded.

Standard lists are a just a list of one or more communities. They can be identified by a name, a number, or the word standard, and are created by using any of the following commands:

awplus(config)# ip community-list <1-99>{denypermit} {aa:xx internetlocal-asno-advertiseno-export}

awplus(config)# ip community-list <list-name>{denypermit} {aa:xx internetlocal-asno-advertiseno-export}

awplus(config)# ip community-list standard <list-name> {denypermit} {aa:xxinternetlocal-as no-advertiseno-export}

If you have more than one community in an entry, separate them with spaces.

Page 28 Use Route Maps and Other Filters to Filter and Alter BGP and OSPF Routes