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New Member

ISDN Backup for VPN Tunnel


I read something about this in the forums , but i didn't find an solution for this problem. This is the situation:

2 Sub Locations with

VPN 1751 with SHDSL Wic and ISDN Bri S/T


VPN 2651 with SHDSL Wic and ISDN BRi S/T

If the tunnel is down , the isdn has to make the connection to the remote sites.

When the tunnel comes up, traffic should past the tunnel and the isdn should go down.

I configured a Tunnel interface and use ospf as routing protocol

i have a static route (host) to the other site of the tunnel.

In OSPF i only define the internal networks including ISDN

When the tunnel is up ospf is learning the other site through the tunnel

I used dialer watch to monitor if the route is up, when the tunnel is down isdn is making the connection, but i can't ping the other network ?

In the examples i found, they use OSPF on te WAN interface, but this is not possible for me, because i use the internet and shdsl !

Who can help me with a suggestion, i think i'm close to a solution.

The routers are in a testlab.

1751 ---- 2651 ------ 1751

The 2651 is only configured for routing between the two 1751 and not configured for ospf or other routing protocols.

The 2651 is a simulation of the internet.

Thanks for helpning me out,

Edwin Gerritsen

Dhs Informatisering

06 50647271

New Member

Re: ISDN Backup for VPN Tunnel

You should consider setting up a GRE tunnel on your IPSEC connection. This will give you the ability to run OSPF on the WAN/Internet side.

Here is a link that should help:



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