Re: Multiple internet connections routing.

From: Abdullah Ramazanoglu (
Date: 07/07/04

Date: Wed, 07 Jul 2004 03:17:57 +0300

Nirnimesh wrote:

> I have two internet connections for my network. How can I setup
> routing
> such that if one of the internet connections is down, the other
> one is used. I'm using a proxy server (squid on RH 9.0) through
> which all the users in my network connect, and it has a static
> route (route -n).
> Nirnimesh.

A lot depends on specifics of your network.

- If you don't want load balancing, but just fail-over, then you
could devise a small script that establishes the second connection
and changes routing table accordingly (assuming both connections
end up on the same gateway machine) whenever first one fails. You
could even find packages out there on sourceforge to streamline

- If you connect through a multi-port modem, it probably does load
balancing and fail-over in firmware.

- If you connect through different service providers, you could run
BGP to route to shortest-path, thus achieving a certain degree of
load balancing in addition to fail-over.

- There should be load balancing features in 2.4/2.6 kernel but I
can't talk about the details off the top of my head (I had skimmed
but not used them). You might want to investigate the relevant
kernel config options.

- If you primarily serve to internet, you could serve DNS on both
connections, each advertising its own public address, and then
register their addresses as your primary and secondary DNS servers
at the registrar. So, if one of the connections is broken, visitors
won't get DNS reply and try secondary, which will advertise its own
(working) public address. This would only achieve fail-over though.
If you also want load balancing, then your primary DNS server
should serve roun-robin between its own public address and the
other one, and you should again devise a script to disable
round-robin serving should the other connection breaks, and restore
roun-robin operation when other connection is reestablished.

- There is also multi-line ppp option but I guess it's not
applicable since it requires both connections terminating on the
same ISP and running PPP-ML on both sides (your control over both
PPP (leased line) and the ISP).

Without having your specifics, these are just a few ways I could
imagine right away. Others can suggest brighter ideas.

Abdullah        | aramazan@ |
Ramazanoglu     | myrealbox |
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