BGP Conditional default-route advertisement

BGP Conditional default-route advertisement

Conditional default-route advertisement is done by associating a route-map with the “neighbor default-originate” statement. The default route is advertised if the route-map matches the prefix which is in the routing table.If the route is not in the routing table, the related prefix will not be advertised to the neighbor.

We can match ip prefixes with the route-map using either access-lists or prefix-lists.

Here is the example:

We will send default-route when 10.1.10.0/24 network is in the routing table:

ip prefix-list test seq 5 permit 10.1.10.0/24

route-map test permit 10

 match ip address prefix-list test

router bgp 1

 no synchronization

 bgp log-neighbor-changes

 bgp redistribute-internal

 timers bgp 10 30

 neighbor 10.10.10.6 remote-as 1

 neighbor 10.10.10.6 default-originate route-map test

 no auto-summary

R1#sh run int f0/0.10

Building configuration...

Current configuration : 112 bytes

!

interface FastEthernet0/0.10

 encapsulation dot1Q 10

 ip address 10.1.10.1 255.255.255.0

 end

R1#debug ip bgp update (to see updates)

BGP updates debugging is on for address family: IPv4 Unicast

R1#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#int f0/0.10

R1(config-subif)#shut

R1(config-subif)#

*Mar  1 00:28:52.063: BGP(0): 10.10.10.6 send unreachable 0.0.0.0/0

*Mar  1 00:28:52.063: BGP(0): 10.10.10.6 enqueued default-originate update

R1(config-subif)#no shut

R1(config-subif)#

*Mar  1 00:29:00.031: BGP(0): 10.10.10.6 enqueued default-originate update