comcast and verizon

[adler-wRvlPVLobi1/31tCrMuHxg at public.gmane.org (Stephen Adler)]

Guys,

I'm planning on switching over to verizon fios, but before I do, I want 
to test the two out. As it stands now, I have both comcast and verizon 
fios in my house.

What I would like to do is setup my servers such that each can talk to 
either the comcast or verizon network cards. Here's what I have

eth0 - comcast
eth1 - verizon

Now the problem I'm having is that if I set the default router to be the 
one which goes through the comcast network, then I can only ssh into my 
system from the comcast ip address. When I try and ssh to the verizon ip 
address for eth1, it does not connect. Likewise goes for the verizon 
side. If I set the default route to be through eth1 and the verizon 
network, then I can ssh to the verizon ip address on eth1 but not the 
comcast one on eth0.

What do I have to do to have both up and running? Do I need to setup my 
server as a router with ip forwarding and all that?

thanks. Steve.