14-SEP-2012: You Can't Get There From Here (Policy Based Routing) r1 (See the current copy)
Which way do I go ? Well, you see... the problem is... you can't get there from here
Occasionally in the course of server management it becomes desirable, or sometimes even necessary, to configure a UNIX or Linux system with network interfaces on multiple networks.
On the surface, the problem appears straight-forward. It may indeed be as simple as it sounds depending on what you do after configuring the network interface. Often times, however, after configuring the network interface and reaching that early success an enterprising system administrator will then say themselves "Excellent, I now have an address on this network now I want to be able to reach it from other networks ! I know, I'll add a route !" and off they go.
They'll do (Linux):
# route add default gw 10.230.5.1
or sometimes, being slightly more aware of routing:
# route add -net 10.55.88.0/24 gw 10.230.5.1
Sometimes this will work. Sometimes this will work poorly. Sometimes this will not work at all. It all depends on what the route is, and what the router that you are forwarding packets to does with those packets.