Re: PPPoE Modem hangup after random time - how to debug?

James Carlson
2020-04-22T22:00:52Z

On 2020-04-22 13:45, David BalaÅ¾ic wrote:
> Hi!
>
> I have a router running openwrt connected to a GPON ONT, running a
> PPPoE connection (hw details below).

This looks to be (possibly) a PPPoE failure, though there's nothing
interesting in the log messages provided. If there were an interesting
log message, it would almost certainly come somewhere (perhaps even
*minutes*) before that initial "Modem hangup" message.

The definitive test would be to run a packet capture on the Ethernet
interface itself (*not* on the PPP interface) with something like
Wireshark and determine what happens in the lead-up to the failure. I'd
expect the system is just getting a stray PADT from the peer, if it's
some kind of PPPoE problem.

If it isn't, then possibly it's something else. I think that the last
time I looked at the PPPoE implementation on Linux it was a bit hokey --
it ran PPP over a pty pair and then decoded the framing in user space
and wrote it back out over Ethernet using PPPoE. I hope it's not still
like that, as I haven't looked at it in years, but it may well be. An
internal error in that logic could also cause a "hangup" message,
although hopefully along with some kind of system log about a core file
as well.

(The implementation on other platforms, such as Solaris, was a bit more
solid.)

--
James Carlson 42.703N 71.076W <carlsonj@workingcode.com>