2 Internet Links x 1 LAN

[breno.moiana@partekforest.com]

Greetings!
I have a very unusual setup here. I have researched on three-connections
firewall setups, and the most common types are either two LANs and one Internet,
or one LAN, one DMZ and one Internet connection.

However, it is my intention to have two internet connections and one LAN
connection on my firewall. They would be a wide ADSL connection, to be used for
heavy traffic as web browsing and downloads, and a smaller, but more reliable
connection to be used by the mail system. It would be interesting to have some
automatic load balancing on them, so that if one link fails, the other assumes
its functions.
Calling "Link A" the small, but high quality one, and "Link B" the wide,
lower-quality, I would make something like this:

LINK A:
e-mail, special services (specific ports, like, for example, Lotus Notes)

LINK B:
everything else (http, ftp etc)

I know how I can allow a service/port to "go out" throug a specific interface
(for :
iptables -A FORWARD -p tcp -o $EXT_IF -i $INT_IF -s $INT_NET --dport 80 -j
ACCEPT

being INT_IF, EXT_IF, and INT_NET, the internal and external interfaces and the
internal network.
I could also tell the linux how to route to specific IPS through an interface
other than the default.

The question is: How could I implement port-based routing? I would like to have
LINK B as default, and the few specific services that I wanted to go through
Link A would be explicitly configured to go that way.

Any ideas?

Regards,

Breno Moiana
-------------------------------------------------------------
"Science is organized knowledge. Wisdom is organized life."

"Ciência é conhecimento organizado. Sabedoria é vida organizada."
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