[plug] Another network question (IP Aliasing)

[Leon Brooks]

On Tue, 10 Jun 2003 12:51, Ryan wrote:
> Supposedly iproute2 can route via aliased IPs, is that the sort of
> thing that would fix this issue (after a lot of reading)?

Yes.

I also use iproute2 for multi-homing sites. You tag traffic inbound on 
one interface to be routed through an alternate table, then set a 
different default route in that table. Here's a recipe:

    ip route add default via 202.181.72.53 dev eth1 \
      table $ISP1 src $INTERFACE1
    ip route add default via 172.31.22.178 dev ppp0 \
      table $ISP2 src $INTERFACE2
    ip rule del from $INTERFACE1
    ip rule add from $INTERFACE1 table $ISP1 priority 1010
    ip rule del from $INTERFACE2
    ip rule add from $INTERFACE2 table $ISP2 priority 1000

You can even do the tagging split with weighting, like this:

    route del default
    ip route add default scope global \
      nexthop via $GATEWAY1 dev eth1 weight 3 \
      nexthop via $GATEWAY2 dev ppp0 weight 2

This sends 60% of your outbound connections through eth1 and 40% through 
ppp0. I used that on a site which was committed to $ISP1 (who shall 
remain nameless except to say that they bought a several other local 
ISPs but aren't iiNet) for some time but they were expensive for 
traffic (haggled down to 10c/mb from 14c), so they got a DSL from $ISP2 
(WestNet, I'm sure they won't mind the promotion) which gives them a 
swag of gigabytes for free and only charge half the rate for bytes 
over. We adjusted the weights to minimise costs.

Cheers; Leon