Administrator Guide

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Filtering Routes with Community Lists
To use an IP community list or IP extended community list to lter routes, you must apply a match community lter to a route map and then
apply that route map to a BGP neighbor or peer group.
1 Enter the ROUTE-MAP mode and assign a name to a route map.
CONFIGURATION mode
route-map map-name [permit | deny] [sequence-number]
2 Congure a match lter for all routes meeting the criteria in the IP community or IP extended community list.
CONFIG-ROUTE-MAP mode
match {community community-list-name [exact] | extcommunity extcommunity-list-name [exact]}
3 Return to CONFIGURATION mode.
CONFIG-ROUTE-MAP mode
exit
4 Enter ROUTER BGP mode.
CONFIGURATION mode
router bgp as-number
AS-number: 0 to 65535 (2-Byte) or 1 to 4294967295 (4-Byte) or 0.1 to 65535.65535 (Dotted format)
5 Apply the route map to the neighbor or peer group’s incoming or outgoing routes.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | ipv6-address | peer-group-name} route-map map-name {in | out}
To view the BGP conguration, use the show config command in CONFIGURATION ROUTER BGP mode. To view a route map
conguration, use the show route-map command in EXEC Privilege mode.
To view which BGP routes meet an IP community or IP extended community list’s criteria, use the show ip bgp {community-list
| extcommunity-list} command in EXEC Privilege mode.
Conguring BGP Fast Fall-Over
By default, a BGP session is governed by the hold time.
BGP routers typically carry large routing tables, so frequent session resets are not desirable. The BGP fast fall-over feature reduces the
convergence time while maintaining stability. The connection to a BGP peer is immediately reset if a link to a directly connected external
peer fails.
When you enable fall-over, BGP tracks IP reachability to the peer remote address and the peer local address. Whenever either address
becomes unreachable (for example, no active route exists in the routing table for peer IPv6 destinations/local address), BGP brings down
the session with the peer.
The BGP fast fall-over feature is congured on a per-neighbor or peer-group basis and is disabled by default.
To enable the BGP fast fall-over feature, use the following command.
Border Gateway Protocol (BGP)
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