routing based upon port, not ip
Le Trôle
We've got isa 2004 with two network adapters.
Three adsl lines available. I don't expose isa directly to the internet.
Each adsl uses a dlink router as a firewall. The external interface
of isa 10.0.0.4 sees them as 10.0.0.1, 10.0.0.2, 10.0.0.3
10.0.0.1 for general web browsing
10.0.0.2 for the company websites that live at www.mydomain.com
and at www.myotherdomain.com, and at www.mylastdomain.com
10.0.0.3 has fixed ip with reverse dns to mail.mydomain.com
How the heck can I do it?
Now, here lies the rub. I can set the gateway of isa to 10.0.0.1, and
specify routes, based upon ip, of course, for the company websites
on 10.0.0.2. I'd like to be able to tell only smtp traffic to use 10.0.0.3,
but I can't. It seems as though smtp can't be routed to the third.
I'm currently stuck with having the mailserver and general browsing
using the same 10.0.0.1 gateway.
The only option I see, and it is described only to illustrate the problem,
is to add a default route to 10.0.0.3 based purely upon ip for each and
every external mailserver where we may happen to send mail. It would be
nice if all traffic for port 25, regardless of ip, was sent to the third
adsl line.