I've inherited the support of two internet-facing 7206VXR routers used as the BGP tier / Internet ingress-egress point of my organisation. We have three ISP services split between two data centres and an iBGP peering between the two 7206s. Each ISP has two BGP sessions - one to the 7206 that their circuit is connected to and another to the 7206 in our other data centre. What I'm trying to understand is why they have been configured this way and what benefits (if any) it gives over just having a single eBGP session between each ISP and the local 7206 and the iBGP session between the two 7206s (which are both within our one AS)?
I've attached a high-level diagram that shows what I'm trying to explain!
thanks in advance