Redistributing BGP routes

Hi,

I know that by default BGP does not allow redistributing iBGP routes into an IGP unless I use the “bgp redistribute-internal” command but why is that? What is the danger in redistributing the iBGP routes is it because the BGP routes might be to much for the IGP to handle?

Thank you,

Victor

Hi Victor,

The primary reason is that it might introduce loops in your network. iBGP has a very high AD (200) so if you redistribute iBGP prefixes in an IGP then any routes learned through whatever routing protocol will replace them:

  • EIGRP External (AD 190)
  • OSPF (AD 110)
  • RIP (AD 120)
The secondary reason is that redistributing a lot of prefixes in an IGP might not be a good idea :)

Rene

 

Thank you!

Hi Rene,

I have a question relating to redistributing eBGP into OSPF…

I have a router running both BGP and OSPF. This router has eBGP connections to other routers and routes learned from the eBGP peers are the routes i want to advertise into my OSPF domain.

I have configured mutual redistribution using route-map’s and the routes are redistributed just fine and all appear in the routing tables as expected. However, another OSPF router (not running BGP) has learned the eBGP routes as i wanted but with an incorrect next-hop. As this router isn’t running iBGP, how do i change the next-hop-self so OSPF advertises the redistributed routes with the correct next hop instead of the eBGP next hop?

Hi Richard,

Do you only have one router that is doing redistribution? If so, is it not easier to use a default route in your OSPF domain instead of redistributing the eBGP prefixes?

You can’t change the next hop directly in OSPF. You could advertise the network that has the next hop in OSPF, or you might be able to get this working by messing with the OSPF forwarding address.

Rene