linux failover (redundant internet/dial backup)

I have question about Linux routing I guess. I want to create a
backup connection to the internet. I will have a DSL line to the
internet and a dialup modem for backup. What I want to do is put a
higher metric on the dial up line. How will it know to switch over to
the dial up line when the Ethernet line is down. Which distribution
will work for this, I will have two Ethernet cards and a modems. Do I
need a default route for my main internet provider. Thanks Mike D

On Feb 26, 5:31 am, mdiac...@yahoo.com wrote:
> I have question about Linux routing I guess. I want to create a
> backup connection to the internet. I will have a DSL line to the
> internet and a dialup modem for backup. What I want to do is put a
> higher metric on the dial up line. How will it know to switch over to
> the dial up line when the Ethernet line is down. Which distribution
> will work for this, I will have two Ethernet cards and a modems. Do I
> need a default route for my main internet provider. Thanks Mike D

The usual way this is handled is to have two default routes. The
higher-priority one uses your DSL and the lower-priority one uses your
dialup link. If the DSL route goes away (you will need to make sure
the route goes away if the link is inoperative), packets will take the
lower-priority route, which will trigger your dialup link to dial.

This is a somewhat tricky thing to set up. Google is your friend. Here
are the things you need to do:

1) Arrange things so that if your DSL link is not working, the default
route goes away. A route will go away automatically if its gateway is
not reachable.

2) Create a lower-priority default route that will cause your dialup
to auto-dial.

3) Test everything.

DS

On Tue, 26 Feb 2008 05:31:21 -0800, mdiaczyk wrote:

> I have question about Linux routing I guess. I want to create a backup
> connection to the internet. I will have a DSL line to the internet and
> a dialup modem for backup. What I want to do is put a higher metric on
> the dial up line. How will it know to switch over to the dial up line
> when the Ethernet line is down. Which distribution will work for this,
> I will have two Ethernet cards and a modems. Do I need a default route
> for my main internet provider. Thanks Mike D

Linux Advanced Routing and Traffic Control guide should have what you
need. There is extensive info about this in their mailing list archive
as well.

http://lartc.org