[ALUG] Routing/port forwarding question

If I set up a 'router' box which does connection sharing with something like the following in its routing:- ip route add default scop global \ nexthop via 192.168.0.2 dev eth0 weight1 \ nexthop via 192.168.0.3 dev eth0 weight1 (two ADSL modems/routers on 192.168.0/24 with approximately equal speed) Then how do I deal with SSL, incoming SMTP and similar which require that, once started, the 'session' continues to use the same interface? Is there a routing syntax that allows one to specify a port number which would override the above for specific port numbers? -- Chris Green