Can adjacent AS in BGP run same protocol in IGP?

Question

I am trying to create a BGP simulation in GNS3.

I have the following topology

Here's what I have understood:

R1 will advertise 201.10.10.0

R2 will advertise 203.0.2.0

R3 will advertise 203.0.2.0

R4 will advertise 203.0.4.0, 205.0.0.0, 205.0.0.128

Since, the next hop is not changed in iBGP sessions, I will either have to use neighbor next-hop-self command or add IGP.'

I am adding IGP. In AS 200 for R3 I will have to add 203.0.2.0 and 203.0.3.0. Similarly for R2 I will have to add 203.0.1.0 and 203.0.2.0.

If I choose to add RIP or OSPF with same process ID in AS 200 and AS 300 then doing IGP will share the routing information of AS 200 and AS 300 with each other using IGP. How do I fix this?

Answer 1

The answer is actually very easy: make sure R3 and R4 do not form an IGP neighbor relationship. You do this by configuring the serial interface between those routers as "passive" only.

A passive interface does not send or receive routing protocol updates, but it is advertised in the routing protocol. For RIP you configure this:

router rip
    passive-interface s0/0

OSPF configuration is left as an exercise for the reader.