Keeping the VPN active?

[mike.botha]

At the Head end I have a 2600 router with a static IP and configured to use a pre-shared key and dynamic crypto maps.

On the remote sites I have 877 and 857 routers connected to ADSL lines. The IP addresses are negotiated.

I am using dyndns.org to overcome the negotiated IP.

What is the best way to keep the VPN tunnel active?

[gfullage]

To keep the tunnel up you need traffic to be flowing over it. The easiest way to do this is to setup your head-end router (or a host on the head-end network) as a NTP server (Network Time Protocol). Then setup your spokes as NTP clients and source the NTP packets from the inside interface, they will send regular, very small NTP update packets to the head-end which will keep your tunnel up. This has the added advantage of keeping all your times in sync for logging purposes, etc.

On the head-end router do the following:

ntp master 5

and on each remote site router then do:

ntp server source

This will make each remote site router send NTP packets, sourced from its inside interface, to the inside interface of the hub router. Assuming that this matches your crypto ACL this traffic will keep the tunnel up.