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[wlug] ADSL failover

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Craig Box craig@d...
Thu Feb 13 10:42:41 NZDT 2003

Hi everyone,

I'm currently investigating how to set up ADSL failover.

The default gateway on the network is a Linux machine, and its default
gateway is a Nokia M1122 connected to Tempest.  In case the Tempest
connection goes down, I would like to set the machine up to fall back to a
secondary route, connected to a Jetstream modem.  The Jetsream connection
should only ever be used in the case that the Tempest connection is

How I've thought this should work:

- set a route for both modems, giving the Tempest modem a higher metric
(this might not be necessary?)
- periodically discover the connection state on the Tempest connection using
a script of some sort 
  - if fine, do nothing 
  - if not fine, set default route to Jetstream modem and start script
watching Tempest connection

The script watching the Tempest connection needs to see if the connection is
up, and when connectivity returns, change the route back to the original

Mail failover will be handled automatically using MX records, so that if
Tempest is unavailable from the outside world then delivery will be
attempted to the Jetstream connection, 

Would a ping test fired by something like Nagios be enough for this task?
The modems support RIP, but I'm not sure what I'd need to do with the Linux
machine to use it, and if it's overkill?  Am I missing anything?

I promise to wiki the answer.


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