[strongSwan] Route VPN server traffic via IPIP tun0

[Igor]

I have a tun0 interface by IPIP tunnel like:

tun0      Link encap:IPIP Tunnel  HWaddr
          inet addr:10.1.1.2  P-t-P:10.1.1.1  Mask:255.255.255.255

How can I route all VPN traffic through the tun0 interface on the
server instead of default route, tried leftnexthop=10.1.1.1 but it
doesn't work.

Thanks!

Bests,
-Igor