iBGP prefix problem

Why is that when I establish an iBGP relationship between R1 and R2 I cannot receive the routes originating from R4?

But when I establish an iBGP relationship between R1 and R3 then I see the prefixes in R1?

*R2 is peered with R3 and has the routes that I want installed int its routing table

bgpquestion.jpg

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NetworkVeteran

Why is that when I establish an iBGP relationship between R1 and R2 I cannot receive the routes originating from R4?

A router won't advertise routes it learns via iBGP to another iBGP neighbor.

But when I establish an iBGP relationship between R1 and R3 then I see the prefixes in R1?

Because in that case the above rule doesn't apply.

When in doubt, full-mesh your iBGP.

mochaaddict

Might also want to play with route reflectors or confederations to get around the iBGP full mesh requirement.

vishaw1986

In IBGP we need a fully mesh network , this a type of BGP split horizon route (for loop prevention )......

e.g
A

C , A is neighbor to B and B is neighbor to C

Now the route learn by B through A is not fwd to C and ViceVersa

mguy

NetworkVeteran wrote: »

A router won't advertise routes it learns via iBGP to another iBGP neighbor.

Because in that case the above rule doesn't apply.

When in doubt, full-mesh your iBGP.

So this means all iBGP peers must be peered with the edge router (the router with an eBGP connection).

Thanks for the rule

mattau

if you want to use the general rule of ibgp peering like discussed, other wise make R2 a route reflector.