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New Member

VPN Connection over different interfaces

We want to start using our 1720 routers to connect to offices using VPN over internet. Both offices have a serial connection to the internet and extra ISDN connections for backup. For normal operation we want to use the serial link to the internet to connect the offices using a VPN.

Now my question. Is it possible to use the ISDN lines to forsee in some extra bandwith if the bandwith of the serial link is not sufficiend. A sort of BOD but the over two different media's. (ISDN line's will connect directly to the other router not to the internet).

Can somebody help me out with this problem


Cisco Employee

Re: VPN Connection over different interfaces

Hmmmm, not really. The routers are simply going to look up the routing table to see which interface they should send the packet out. This interface also happens to have a crypto map on it and so the traffic is encrypted. You could apply the same crypto map to the ISDN interfaces, but the trouble is there's really no way to tell the router to use these interfaces if the Internet connection is slow. It's all to do with routing on the local router, and the route to the remote network will point out your Internet-connected interface. There's no way either router is going to now if the Internet is slow or congested.

New Member

Re: VPN Connection over different interfaces

I was affright for this answer. Somebody told me go build this. Its a cisco so it should work. But thanks for the answer. We will set the ISDN interfaces as backup. This shoud work if I set the metric for the route over the ISDN interface higher then the metric on the route over the SERIAL interface.

Thanks for the fast responce.


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