Re: Automatic ISP failover if connection fails
--- Albert Ulmer <jayaeu@gmail.com> wrote:
> 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
> lost.
>
What happens is the routing code detects that the metric 0 path isn't
working and it starts using the metric 1 part. The thing that may be
tricky for you, I don't know ISDN only NICs, is that you must keep the
interface bound to an IP and have routes(that have a higher metric)
attched to it. This means that the interface has to be "ifconfig xxxy
up", but maby not dialed and working.
> > 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....
>
That's what metric is, it's the admins perseption of what routes are
better then others. You could base this only on RTT, but that may be
narrow minded.
> Best regards,
> Albert.
>
>
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