[vox-tech] Using dial-up as backup for DSL

[Ted Deppner]

On Fri, Dec 23, 2005 at 12:33:22AM -0800, Paul wrote:
> Since my DSL was down for about 4hrs today (thanks pacbell/sbc/att) I'm 
> trying to figure out how to setup my server box and a modem as a 
> fallback when my dsl line goes down.

I actually had this setup, although I wrote all the scripts myself.  What
I did was kind of a kludge, but it what exactly what I wanted and
relatively easy to control and extend.

I had PPPOE through SBC at the time, and a standard PPP dialup available
to me.  If you can do some scripting, I can explain and perhaps share some
of my scripts (if I can find them) in more detail.

Essentially, a program "chooser" ran from cron, which looked at what
routes were in the routing table, and then did ping tests.  When PPP links
would come up an ip-up script would add a special route which was
different for each PPP link, usually that providers DNS server.  Chooser
knew which DNS server (and therefore route) was the primary desired.
Lastly, all the links were controllable under DJB's daemontools, so a
simple "svc -u /service/ppp" or "svc -u /service/pppoe" would bring up the
relevant service.  Chooser would itself modify the default route if it
found a link to be up, but it's DNS server to be unresponsive, or that a
more preferred link had just come back up.

-- 
Ted Deppner
http://www.deppner.us/