I have also observed very similar behavior.
I am running kernel 2.4.0-test2 and pppd 2.4.0b2.
The only difference in my case is that if the second link
drops the first one continues to forward fine.
My observation was that the first link brings up IPCP
and runs the ip-up script. If the first link drops
it also shuts down IPCP and runs the ip-down script.
If the dropping of the second line goes undetected
(in my case, I had to add LCP echo to the pppd command
line options to prevent this), then the kernel PPP
continues to forward (and fragment frames) on the down'ed
channel, but the fragment gets dropped by the lower level
driver.
I was planning on adding a cron job that monitors the
primary line and if it drops, it will also drop the second
line and try to bring them back up again. Whoever comes up
first will run IPCP again and things should be peachy.
I am working with nailed up lines though. For modem case,
if you are planning on dropping the links after a period
of inactivity, the cron job needs to take that into account.
Hope this helps and keep me posted if you find out anything
different.
Koral
Software Engineer
Occam Networks Inc.
Chris Gosley wrote:
>
> I have redhat 6.1 "out of the box" which has the ppp 2.3.10-3 driver
> and connected two modems to ttys0 and ttys1, set both through linuxconf
> to dial my Cisco 2511 and turned it on.
> both interfaces came up and dialled and connected, multilink appeared to
> work perfectly.
>
> Then I tried some fault tolerance I turned off one modem, and the link
> failed to route completely, even though the other modem was still
> connected fine.
>
> Am I right in assuming that the first modem to connect get "designated"
> the primary of the two and carries all of the back channel (upstream)
> data, whilst the second modem simply acts as a secondary channel to
> assist in receiving every other packet ?
>
> hmmm, I just tired doing it the other way around and switching off the
> other modem instead (after the first had redialled again), once again
> the remaining modem failed to route, so it appears that if either modem
> fails then regardless of wether the other is connected or not the
> multilink fails.
>
> I don't want to sound dumb, just trying to understand the system before
> I give it to a customer so I know what to expect.
>
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--
Koral Ilgun
Software Engineer
Occam Networks, Inc.
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