WAN for backup to fiber trunks

We have dark fiber ran between our local sites.  Everything is terminated at a 6500 and appears as a locally connected route.  Someone proposed using a DMVPN as a backup should our fiber get severed.  DMVPN doesnt appear to be the correct solution since everything terminates at the 6500.  With 2901 routers in hand is there a way to utilize them to make a trunk port over comcast/att should the fiber go down?

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Bryant SchaperCommented:
So to be clear, you have a 2901 at each end, with a fiber connection at each from Comcast.  You also have a dark fiber at each and you can setup an interface on each and ping the other side ok?

What about IP SLA or giving the route a weight?

How about a diagram?
silvercasAuthor Commented:
We currently have dark fiber ran from main office to several branches.  There are 3750's switches at each branch though routing is not configured on them.  In case our dark fiber was to ever get cut a backup "TRUNK" would be ideal.  I envision hooking the router into a trunk port on the 3750,6500 and the routers handling everything else.
Bryant SchaperCommented:
I really need to see a diagram, I think I conceptualize what you are saying, but dark fiber implies not in use.  So everything is currently running over Comcast now right?

You can use the routers to handle routing for sure.  The diagram will clear up some of my questions and any other expert who jumps in.
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silvercasAuthor Commented:
dark fiber is fiber we light up ourselves and is currently what we use between sites.  comcast/fios is what I want to use is fiber gets CUT.  I dont have a diagram at this moment but I do understand how it helps!

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Bryant SchaperCommented:
ok, so the dark is in use.  Explains a lot more.  I guess I would not consider it dark, but I would be at a loss of what else to label it as.

so how about trying a vpn tunnel over Comcast and then a route weight to send traffic there if the circuit is down.  The fiber circuit will have the highest weight as it appears as a direct connection.
silvercasAuthor Commented:

Do you know what I can search google for examples of what you are explaining?

Bryant SchaperCommented:
try cisco vpn failover configuration
silvercasAuthor Commented:
must change nework over to routed
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