Redundant Interfaces to Same Switch

[TaylorDC]

MSR 3012 router.  I want two interfaces to have the same IP going to different physical switches that share the same subnet.  The purpose is for switch failover tolerance.  There is still a single point of failure in the router, but this is by design.

Attached is a network diagram of what I'd like to be able to do.  Is there a better way that I'm not considering?  Something with the switches, maybe using LACP or something else?

[Ian Vaughan]

Hi,
I would IRF the switches together as this is best for down-stream LACP. I would then do OSPF between the router interfaces and 2 routed (# port link-mode bridge) interfaces on the switches. 2 little /30 "transit" networks should do it.
You can have ECMP for optimized load-balancing or BFD for super-fast failover in this kind of topology.
You can advertise a default route into here and if you ever get a secondary, say DSL, router that also be configured to advertise a more costly route into the switch for use if the primary router ever goes offline.
I would also look to monitor the primary router's uplink - not only for link connectivity but also the routing protocol as quite often the upstream ethernet stays up even when the WAN link goes down.
Best of luck
Ian

[jmpprd]

Good to know