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IBGP Peering not needed but desirable


I have an office with two stacked 3750x switches as collapsed distribution, connected to two 2951 CE routers. The routers are peering EBGP with my service provider using BGP and filtering out all routes except An outbound route map prevents the default being re-advertised into BGP. The routers and switches are all in OSPF area 0 and redistributing BGP received defaults.

I have been peering the CEs using IBGP as I like to be able to check both CEs on a single switch using show ip bgp but the design team are telling me it is not necessary because OSPF is already sharing the default. I like that IBGP peering and am loathe to remove it.

Can anyone think of any other reasons for the IBGP peering or point to a best practice doc I can wave at them?



Peter Paluch
Hall of Fame Cisco Employee

Hi Dave,

To be honest, I also do not see any compelling reason for you to keep the iBGP peering. You say yourself that it helps you to check both CEs using the show ip bgp command. However, that reduces BGP from a complex routing protocol to a verification tool. It is arguable whether the convenience of show ip bgp justifies the need of running iBGP, especially in your setup. It carries the default route only and even this default route cannot be placed into the 3750x stack's routing table because of higher AD. After all, CEs inject the default route into OSPF only if they received it themselves from your ISP via BGP (assuming you are not using the default-information originate always in OSPF). If on the 3750x stack, only a single OSPF-learned default route is placed into the routing table, the other CE clearly has a problem, and you can tell that easily without having the iBGP running.

It is true that your iBGP does not incur any significant load on the routers and 3750x stack. The value of running it is, however, dubious in my personal opinion. There is no harm in leaving it in place - but the added value of running it is, methinks, negligible.

Best regards,