Hi tlockett
This is a typical request from the server guys as it's simple for them and complex for you to sort safely. VPLS is not an option on the 2911 so that's out of the question.
Do your 2911 have spare routed interfaces that you could use to connect using l2tpv3? If they do that Will be your simplest solution. However be aware that this is not a scalable. Also the performance when running l2tpv3 will take a hit as the router will have to encapsulate the frames, this is a problem at small packet sizes and not ideal. This may also be a limiting factor on the performance of any backup solution run over the connection.
Worst case the volume of replication traffic could hammer the router and put it at risk.
Before you do it check with the server guys how much bandwidth will be required under both normal and failed conditions and make sure the router has the capacity to deal with it.
Meanwhile it may be an idea to encourage them to explore backup solutions that support L3 clustering, automation of gateway switching, possible some clever DNS solutions could help. Pretty much any solution other than l2tpv3.
Sorry not to be more positive but at least you have options.
HTH
