Shorewall users - Jun 2005 - Question about connecting to a cisco vpn concentrator

My company uses a cisco firewall, and I have currently got my firewall 
(shorewall + racoon etc) connected to the company firewall via a vpn 
client called vpnc.  Works ok, but doesn''t to rekeying, so it dies
after
about 4 hours.  I should be able to use racoon to do this, but I can''t 
get the config right.
Any hints?
wcn