Gerry George <[EMAIL PROTECTED]> writes:
> I am considering a situation where a remote site is being connected via a
> 64k leased line. This line has a backup ISDN link which, with the
> telecom-provided router will automatically dial out via ISDN in case the
> leased line drops.
>
> I would like to replace this with a Linux system if possible - one already
> exists as a server at the remote site. I am considering a WAN card (ex.
> Sangoma WanPipe) plus an ISDN adapter. I assume that using diald, once the
> 64k line drops then a dial-out will be initiated. However, as soon as the
> line is reactivated, it should drop the ISDN line (very expensive usage
> charges) and revert to the WAN card.
It should be possible. You want your Linux box to act as a dynamic router.
All you have to do is become a high-power network administrator :-O
I'm thinking of something like this:
1) a diald configured to bring up the ISDN line,
2) a default route to the diald proxy, but with a bad metric,
3) a daemon such as gated(8), to monitor the status of the leased
line and maintain a default route through it, with a good metric.
The idea is that when the leased line fails, gated removes the good route,
the kernel starts routing packets through the diald proxy and diald brings
up the ISDN line. When the leased line comes back, gated restores the
good route, the ISDN connection goes unused and diald brings it down
after it times out.
Issues:
1) What happens when the leased line goes out? Does the corresponding
network interface get ifconfig'd out? Can gated notice?
2) What happens when the line comes back up? Same issues.
3) Will diald and gated get into a fight over the routing tables?
That one can probably be managed by writing diald `addroute' and
`delroute' scripts that are compatible with gated.
You might want to try this out internally with a couple of ethernets or
serial lines before you commit to the leased line and the ISDN line.
Disclaimer: I am NOT a high-power network administrator !!
--Pierre Asselin
Colorado
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