I have in my office two Catalyst 4000 switches that do layer 3 routing. HSRP is used on all vlans, so that one switch acts as primary and the other as failover. The HSRP address of each vlan interface is configured as the default gateway on all connected workstations.
For connecting to the WAN, I have two routers (with same BGP AS, directly connected back to back running iBGP between them). I intend to connect one to the primary switch and one to the backup in order to get as much redundancy as possible. Now, since these routers are in active-active mode (load balancing), I am not sure how to make a layer 3 design that allows my primary core switch to load balance traffic to the WAN over both routers.
My first idea was to create a "link VLAN" with a /30 netmask between each switch and router pair, run iBGP between the switches and eBGP between each switch and router, but after reading a bit about this, it seems like BGP would always prefer the locally connected router. My other idea was to create one vlan that spans both switches, and put both routers and switches on the same layer 3 segment, then run iBGP between the switches and eBGP between each switch and router pair.
Hope this explanation makes sense to someone.. All help is much appreciated!
Cat4000 -------------- Cat4000
Router1 ---- iBGP ---- Router2