iBGP between Dual ISP Routers

[snarayanaraju]

Hello All - Refer the diagram attached. What is the advantage or requirement of configuring iBGP session between Router 1 and Router 2.

learning prefix 10.1.0.0/16 in R1 using eBGP between R1 and R3
learning prefix 10.1.0.0/16 in R2 using eBGP between R4 and R2

Using network command in R1 and R2, advertising 192.168.1.0/24 to R3 & R4 respectively

EIGRP between R1 and LAN L3 Switch. Redistribute BGP to EIGRP

EIGRP between R2 and LAN L3 Switch. Redistribute BGP to EIGRP

regards,SAIRAM

[paul driver]

Hello

when you have external bgp peerings (ebgp’s) especially between different isps then running an internal bgp (ibgp) between your internal wan rtrs will provide routing resiliency between each iisp for you internal network as each Ibgp neighbour will advertise its ebgp learned routes to each other so each rtr will beaware of the others learned external routesBthen if you desire you could redistribute these learned prefixs into your internal network 

[snarayanaraju]

Thanks Paul - What is the advantage of using iBGP between the WAN Routers as each prefixes i learn from eBGP is getting redistributed EIGRP and my Core switch is going to decide what is the next Hop.

[paul driver]

Hello

I don't see any attached diagram?
If you dont have a IBGP relationship then if you lose connection from your lan core to either one of those rtrs then you lose connection to its related ISP, However if the ibgp relationship existed then connectivity wouldn't be lost as traffic would be routed from your core switch via the remaining rtr over its ibgp peering then out towards the isp you lost connection to via the core switch.

[snarayanaraju]

Thanks again. I understand the resilenccy you refer. Specific to the topology i refer in the attached diagram What is the disadvantage i will have if I don't have iBGP between these WAN routers

[paul driver · Accepted solution]

Hello

As above...

[snarayanaraju]

Thanks, It makes sense. However the diagram is attached for your reference