Injecting IGP routes into BGP

Posted in NETWORKING/IP ROUTING by edeguzman on October 3, 2007

This is a configuration wherein routes in the routing table is place in the BGP table.
The routes in the BGP table will be advertised to its BGP peer whether its inter-AS or
intra-AS. Below is the configuration.

router eigrp 200
passive-interface s0
network 192.168.1.0
network 192.168.100.0
!
router bgp 200
redistribute eigrp 200
neighbor 192.168.1.226 remote-as 100
!

The configuration shows that I used the EIGRP as my IGP running within the AS 200,
a passive-interface is configured in its process, wherein it means that in the interface serial 0 it will not advertise neither receives updates and it will not even send a hello packet in that interface.

In the BGP process, a redistribute eigrp 200 is configured this will simply redistribute the routes learned via EIGRP into the BGP table. You can see its results by making a show ip bgp, from there you can see the routes of EIGRP that is distributed into the BGP table. This configuration is not that good because there are drawbacks using this kind of configuration. Because all the routes learned in EIGRP is place in the BGP table in which in some cases this is unacceptable. There are routes in EIGRP that you might not consider to be part of your BGP table. Another reason is the problem of route feedback, when using redistribution the route feedback is always a possibility in your network. Because of this you must apply route policies to compensate the
situation.

Below is another configuration of injecting IGP routes into BGP.

router eigrp 200
passive-interface s0
network 192.168.1.0
network 192.168.100.0
!
router BGP 200
network 192.168.1.216 mask 255.255.255.252
network 192.168.100.0
network 192.168.200.0
neighbor 192.168.1.226 remote-as 100

As you observe in the BGP process, that a network command replaced the
redistribution command. This is better way than redistributing because you
had fully control on the networks that you want to include in your BGP table.