I am running into the problem, I have played around with it some, but most of the work I have done has been on production environments that I couldn't break.

Essentially what I have is the need to hook multiple DSL modems into a routerboard, draw DHCP addresses. some of which might be in the same subnet using the same default gateway, then route traffic from specific VLANs over specific modems. I have obviously used srcnatting to get the traffic to come in the way I want it, but all of the traffic going out goes over whatever interface the route table sees the default gateway on.

I think I may have figured it out. Will write back once I have time to test.

I have several PPPoE - ADSL setups which look the same, i.e. the gateway is 192.168.153.1 for all (up to 4) of the PPPoE connections.

It doesn't seem to matter, probably because the gateway is the interface, not the IP.

I have to admit that i looked at it and thought WTF when i first saw the same gateway IP on all of the connections.