[clug] Multi-homing

Dennis M. Gray d0325mgray at fareast.com.au
Wed Jan 28 01:30:03 GMT 2004

I've had several responses but I think you have the idea of what I
am trying to do.

1. The permanent dial-up on ppp0 is running services that I will
move to the ADSL. I will then discontinue the permanent dial-up.

2. I only want to run both interfaces at the same time because I am
in Canberra and the box is in Sydney. I want to SSH to the box on
the ppp0 and be able to configure and test the ADSL on eth0.

3. The source based routing solution sounds like what I am looking
for but I would need to upgrade to be able to do that. I do want
connections coming in on the dial-up to go out on the dial-up and
the same for the ADSL, like you said.


Martijn van Oosterhout said:
> On Wed, Jan 28, 2004 at 11:48:56AM +1100, Dennis M. Gray wrote:
>> I have been running a Red Hat 7.1 distro with a permanent
>> dial-up to my ISP. I intend to stop using that and have added
>> an ADSL
>> service on another phone line. I am using the eth0 NIC for the
>> ADSL.
>> For a short period I want to enable both interfaces. When I
>> bring up the eth0 at the same time that the ppp0 is up, I can
>> no longer communicate via ppp0. The two interfaces are on two
>> completely
>> different networks.
> One of your problems is that both links will try to set a
> default route.
> Secondly, do either of your providers allow asymetric routing?
> If not, you need to get down and dirty. I presume you're
> running some kind of service on the permanent dial-up or you
> wouldn't be considering keeping it.
> The real solution is source based routing. So connections that
> come in your dialup go out the dialup and the same for the
> ADSL. For that you need the new iproute2 stuff in 2.4+. Try the
> LARTC (www.lartc.org) but the basic idea is below. Note, if
> have only setup it up with static IPs, if either of the IPs is
> dynamic you could be be into some fun. Also, this probably
> isn't the only way to do it, I'm sure there are some fancy
> netfilter modules that could do it also.
> Hope this helps, though I admit it can be quite confusing...
> Multi-homing is a pain. Do you really want this?
> --- begin ---
> # Lookup normal routing table but at priority 500 instead of
> 32766 ip rule add lookup main prio 500
> # Setup later tables at lower priority
> ip rule add from <dialup ip>         lookup dialup prio 600
> # Everything else
> ip rule add                          lookup adsl   prio 601
> # Set default route for dialup
> ip route add default via <dialup gw>     table dialup
> # Set default route everything else
> ip route add default via <adsl gw>        table adsl
> # Remove default route from main table to make it work
> route del default
> # Clear routing cache
> ip route flush cache
> --- end ---
> --
> Martijn van Oosterhout   <kleptog at svana.org>
> http://svana.org/kleptog/
>> (... have gone from d-i being barely usable even by its
>> developers anywhere, to being about 20% done. Sweet. And the
>> last 80% usually takes 20% of the time, too, right?) --
>> Anthony Towns, debian-devel-announce

Dennis M. Gray
Sydney Phone:    (02) 9310 7907
Sydney Fax:      (02) 9310 7917
Canberra Phone:  (02) 6258 7917
Mobile:          (0418) 646267

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