I've got a nice VPLS implementation with 22 different sites, implemented by 1 carrier (let's call them carrierA).
The boss now wants to have a backup VPLS implementation with a second carrier (let's call them carrierB).
So the end result will be that we will have 2 separate VPLS implementations provided by 2 different carriers.
The million dollar question:
Is it possible to multi-home these things, so that if there is any failure of any of the VPLS lines provided by carrierA, it will fail-over to carrierB?
The hardware I've got at these sites are Catalyst 4500 and 3750 switches, as well as some ISRs.
Ahh good question. The answer is both. It's convoluted.
Some sites are routing over the VPLS, other sites are layer 2 (most of them, actually).
You would rely on spanning-tree to find the best path. If one of your interfaces goes down then it should send traffic to the next available interface. The downfall of ethernet circuits is that the protocol or interface typically doesn't go down when there is an issue. The switch or router will show up/up but actual issues exists and traffic is just being dropped from carrier issues. For that reason I like to setup IP SLA.
For the routing side just set both in the routing table and if you want an active/standby just weight one route higher.