We are in the process of creating a WAN Distribution layer. Prior to implementation, we would redistribute BGP routes learned from our different MPLS carriers into one core EIGRP instance. Our WAN consists of primarily two different routers. One one router, we will call R1, there is a Provider A. On router 2, R2, we have two other providers, Provider B and Provider C.
Provider A and B give us our primary circuits in our remote locations, which typically consist of T1 circuits. Provider C is a DSL provider and allow for a backup connection that is always on. As I said before, all of the Providers are BGP MPLS connections.
Here is the current topology in graphical form:
Problem: Suboptimal Routing for traffic because of the common redistribution metric that is used between the access routers and the WAN distribution switch.
Scenario #1: For remote location A, the primary circuit is comes from Provider A, and the backup circuit comes from Provider C. Provider A has QoS enabled on the MPLS network, carries voice traffic and is a larger circuit with stricter SLA's. Provider C is strictly a data only connection without any QoS and is not designed at this time to carry voice. Also the links from Provider C are typically smaller. So there would be a drastic performance hit both from the applications and voice perspective. Once the routes are redistributed into EIGRP, both paths become equally in cost and therefore equal cost load balancing will occur when traffic comes from the core through the WAN Distribution switch, with some of the traffic going over the preferred path, over Provider A, and some of the traffic going over the path through Provider C.
Scenario#2: For remote location B, the primary circuit comes from Provider B, and again he backup circuit comes from Provider C.
Solution #1: Rather than distribute routes from BGP to EIGRP on the access routers, create IBGP neighbors between the Access routers and the WAn Distribution switch and use local preference to control the routing for Scenario#1. For Scenario#2, use weighting to prefer Provider B over C.
Solution#2: Rather than create IBGP peers, prepend the Provider's C AS using the AS path prepend, and then adjust the redistribution metrics between EIGRP and BGP on the access routers so that the WAN Distribution will see the preference for the primary circuit to go over Provider A or B.
So which solution would you choose? Why?
Do you have any other ideas?
