How to setup a router with 2 internet connections?

[Christian Pernegger <pernegger@chello.at>]

Hello,

this is probably gonna be long, please bear with me...

I have a small network at home that uses a dedicated router box as
default gateway. The gateway in turn was until very recently connected
to the internet solely via a cable modem, happily
filtering/masquerading away.

Then I got myself an ADSL line additionally, which is also connected
to the router box. (It's potato + 2.4.2-ac20 + a few packages compiled
from sid-source.)

I've only gotten as far as to be able to 'switch' between
connections... :)

What I'd like to do is specify for each protocol the connection it
should be masqueraded out over, with the option to masquerade some
over both. I thought there wouldn't be any problem because you can
list multiple addresses for source NAT, BUT for that to work there
must be a valid route from each of those addresses to the
destination. The thing is, one cannot have 2 default routes.

I've found no way to specify two equal ways to the outside.

Of course I could use ip route's table feature to add two tables
containing the two default routes and select between them using
fwmark.

That has the disadvantage that the same information has to be in each
rule twice (the outgoing address should be enough to select the
interface, but we need fwmark) and there's no way to specify 'SNAT
over one or the other, I don't care', which'd be a godsend for http...

Comments?

Thanks

Christian