Example Advertising Local Networks

In this example, network 1.0.0.0/8 is directly connected to interface Loopback0.

asl23# debug ip routing asl23# debug ip bgp update

%LINEPROTO-5-UPDOWN: Line protocol on LoopbackO changed state to down 1:34:33: RT: interface LoopbackO removed from routing table

1:34:33: RT: del 1.0.0.0 via 0.0.0.0, connected metric [0/0] 1:34:33: RT: delete network route to 1.0.0.0 1:34:33: BGP: route down 1.0.0.0 255.0.0.0 1:34:33: BGP: no valid path for 1.0.0.0 255.0.0.0

1:34:33: BGP: nettable_walker 1.0.0.0/255.0.0.0 no best path selected 1:34:33: BGP: 2.3.4.5 send UPDATE 1.0.0.0 255.0.0.0 — unreachable

1:34:33: BGP: 2.3.4.5 1 updates enqueued (average=25, maximum=25) 1:34:33: BGP: 2.3.4.5 update run completed, ran for 4ms, neighbor version 4, start version 5, throttled to 5, check point net 0.0.0.0 1:34:33: BGP: 3.4.5.6 send UPDATE 1.0.0.0 255.0.0.0 -- unreachable

The route to 1.0.0.0/8 was previously installed in the BGP table because it was listed with a network statement and it was in the routing table as directly connected. When the Loopback0 interface goes down, the router removes the directly connected route from its routing table. Because the route no longer exists in the routing table, it must also be removed from the BGP

Because there has been a change in the BGP table, the BGP neighbors must be informed. The router sends a BGP update message to both neighbors indicating that network 1.0.0.0/8 is now unreachable.

In this example, network 1.0.0.0/8 is directly connected to interface Loopback0.

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