[LARTC] Multiple uplinks through single ethernet

[Chris Bennett]

Next week I'm replacing my single SDSL connection with two ADSL connections. 
I've got a plan for dealing with this, but I'd like any thoughts on 
potential problems I might run into.

My goal is not to load balance the bandwidth (yet), but I do want to run all 
traffic through a single router.  At the moment this router only has one 
ethernet port for both of the ADSL connections (and another ethernet port 
for the local network) so this is my biggest concern.  The example in the 
HOWTO assumes a separate ethernet port for each uplink.

Here's the intended setup:

ADSL 1 = 6mbps/768kbps, several static IPs on 66.92.128.0/24 (gw = .1)

ADSL 2 = 6mpbs/768kbps, several static IPs on 69.17.22.0/24 (gw = .1)


LOCAL NET                ROUTER            INTERNET
                    -----------------
192.168.A.0/24 ----|     <-NAT->     |---- ADSL 1
                   |ETH0         ETH1|
192.168.B.0/24 ----|     <-NAT->     |---- ADSL 2
                    -----------------

For example (to make up some numbers):

subnet A:
192.168.1.2 <-> 66.92.128.2
192.168.1.3 <-> 66.92.128.3
subnet B:
192.168.2.2 <-> 69.17.22.2
192.168.2.3 <-> 69.17.22.3

The default route to the Internet will be 66.92.128.1 via ADSL 1, but all 
traffic for internal subnet B (SNATs to 69.17.22.xx) should instead route to 
69.17.22.1 via ADSL 2.

I think (but correct me if I'm wrong) the command for this is:

ip route add 69.17.22.0/24 dev eth1 src 69.17.22.2

So are there any problems with this setup?  Is there any need for separate 
routing tables if both ADSL connections are on the same ethernet port?  My 
router is a mini-itx so I'm not sure I can easily fit another ethernet port 
in it, but I could look into that would really make things work better.

Thanks!

Chris