ipsec

I have just got ipcomp working between 2 hosts as follows:

• Install the ipsec-tools program
• Add the following config to /etc/ipsec-tools.d/peername.conf
  
  spdadd MY_IP PEER_IP any -P out ipsec ipcomp/transport//use;
  add MY_IP PEER_IP ipcomp 1000 -m transport -C deflate;

  spdadd PEER_IP MY_IP any -P in ipsec ipcomp/transport//use;
  add PEER_IP MY_IP ipcomp 1000 -m transport -C deflate;
  

When using IPSEC, I prefer to use tunnel interfaces so you can route traffic normally across the tunnel and use BGP/OSPF to transfer routes between sites. I managed to get this working from Linux to Cisco as follows, with redundant DSL connections (yuo can adjust to suit your environment):

On the Cisco router:
crypto isakmp policy 1
encr 3des
authentication pre-share
group 2
lifetime 3600

crypto isakmp key Pre-Shared-Key address Linux-IP-Address no-xauth