Fault Tolerant VPN??

[ilyaskhan]

Hi,

I have a dsl router(1721) on 1 site making a dynamic VPN to the fixed IP of a leased line router(1721) on another site.

Now, i want to add an ISDN module on the dsl router, and configure it as a backup interface to the internet. That's to say, I want that in a case where the DSL connection goes down, the isdn dials to the internet and the VPN is formed over it again automatically.Can i expect any complications with the VPN tunnel with regards to this upgrade and if yes, what would i have to do to work it out??

Thanks.

[mheusinger]

Hi,

with respect to the VPN in both cases (DSL and ISDN) you have a dynamically assigned IP address, so there should be no difference.

The tunnel has to be rebuilt once you are connected through ISDN in the backup case. Network outages will be evident, but except from that everything should be straight forward.

Hope this helps

Martin

[aacole]

One problem is that you can get failures downstream in the ISP network, but your DSL link remains active. In this case your backup link doesnt detect the failure and so wont kick in.

To resolve this problem you can use a feature called object tracking. Use it to detect a link failure by pinging a number of reliable Internet addresses via your DSL link. When the echo replies fail the `tracked object' goes down and you can use this to activate your backup.