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Re: Automatic ISP failover if connection fails

On Fri, 8 Oct 2004 16:39:21 +0200 (CEST), Peter Funk <pf@artcom-gmbh.de> wrote:
> > So, I'd really be interested in hearing if there is a good solution.
> > I'm convinced that it can be done!
> The trick is to have two routes with different Metric.  If for example
> ippp0 is your ISDN-device and ppp0 is your DSL connection, you could
> have two default routes: one with metric == 0 on ppp0 and another one
> with metric == 1 on ippp0.  If both pppd-Demons are configured to
> "dial" on demand, the ISDN connection will be established automatically,
> if the pppoed dies for some reason.

OK, sounds reasonable. Can this scheme be adapted to a scenario where
1 NIC (no pppd) and 1 ISDN-card are involved? Putting
up-/down-statements into the NIC-setup won't do much good, as the
NIC-link doesn't go down, even when the connection on the WAN-side is

> Since my setup is little bit different (ISDN goes directly to a computer
> in our company network and is a fallback for the VPN) I can't provide
> a working configuration file.
> Just a guess: you have to insert or modify some 'up' and 'down' commands
> in your /etc/network/interfaces file.  Like so
> ...
> iface ppp0 inet ... # DSL (pppoed)
> ...
>        up route add default gw XXX.XXX.XXX.XXX metric 0
>        down route del default gw XXX.XXX.XXX.XXX
> ...
> iface ippp0 inet ... # ISDN
> ...
>        up route add default gw XXX.XXX.XXX.XXX metric 1
>        down route del default gw XXX.XXX.XXX.XXX
> Read /usr/share/doc/ifupdown/examples/network-interfaces.gz
> for more information.

Is there a way to alter the metric of an interface based on RTT of the
ISP-router on the other side of the link? I guess this would solve
part of the problem....

Best regards,

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