What's the cause of "Timeout waiting for PADO packet" errors?

[#1]

I've been using my own ASUS router for a couple of years without any problems.  It has far more CPU power than the one provided by Plusnet and is far more appropriate for a fibre connection in a family home (ie. where computers, mobiles, smart TVs, etc. may be connecting to the internet simultaneously).

Anyway, earlier today the whole internet went down and the system log was showing this error in particular every few minutes.

"Timeout waiting for PADO packet" 

I rebooted the router to no avail.  I unplugged the router for 15 minutes but that didn't resolve the issue.  Unplugged again for an hour, but nope.  

Then I figured I'd get the Plusnet router out of the loft.  Plugged it in and I had to figure out how to use the admin interface and update the password... and... that resolved the problem!

Plugged my ASUS router back in and that was immediately working again too.

So yeah, my question is in the subject line.  What causes the PADO packet errors?  Why did plugging in a different router resolve the problem for both routers?  And, on the off chance this happens again, is there an easier way to fix it?  Plugging in another router is a hassle due to the way I've got the preferred one setup in my home (wires behind wall panels for the sake of tidiness among other things).

[#2]

strange but since getting a dynamic IP i regularly see this too ?

May 4 00:43:53 WAN Connection: Fail to connect with some issues.
May 4 00:44:09 pppd[536]: Timeout waiting for PADO packets
May 4 00:44:09 pppd[536]: Connected to a0:f3:e4:34:d9:06 via interface vlan3880
May 4 00:44:09 pppd[536]: Connect: ppp0 <--> vlan3880
May 4 00:44:10 pppd[536]: CHAP authentication succeeded
May 4 00:44:10 pppd[536]: peer from calling number A0:F3:E4:34:D9:06 authorized

[#3]

What causes the PADO packet errors?

I believe one possibility is that a previous PPPoE session hasn't been cleared down properly by the disconnect. The system is then not in the correct state to respond to the PADI request and therefore never sends a PADO response.

It's possible to clear down an existing session by sending a PADT request and some routers can(may) do this automatically when starting.. So, when changing to the PN router this may be the case and so any existing session is closed.

[#4]

Thanks MisterW!  That's very plausible.  Come to think of it I only switched back to the official ASUS firmware around a month ago and now i'm wondering if the Asuswrt-Merlin firmware I used previously did a better job of recovering from the PADO packet timeout problem.

I only reverted to the ofiicial firmware out of curiosity so I think I'm going to re-install Asuswrt-Merlin.

[#5]

Yes, some routers/firmware seem to recover from this situation better than others. I recall seeing a few problems like this some while ago but can't quickly find them in the forum at the moment. I believe that eventually the PN system will timeout and close the session but it can take quite a while for that to happen under some circumstances