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Odd network issue - I have a VDSL (fibre-to-the-cabinet) line to home. My router connects via PPPoE to my ISP, and the ISP then sends regular LCP echo packets to monitor the connection and show latency/congestion on the connection.
Recently had a strange fault - I had no "internet" connectivity, but the ISPs echo monitoring was working fine. The PPPoE connection established, and the LCP echo was working, but all IP packets from the ISP down to my router were being lost. Upstream packets from my router to the ISP were apparently being sent correctly.
So the connection path looks like this :-
My router <---> My end of the PPP link <---> backhaul provider <----> ISP end of the PPP link <----> rest of internet
Something was broken between my end of the PPP link and the ISP end of the PPP link. The ISP was saying this was a backhaul issue, the backhaul provider was saying nothing was wrong. But isn't the traffic supposed to be encapsulated within the PPP link? How could the LCP echo get to my router, but not regular IP packets?
David
Posted 2018-06-11T09:59:20.680
Reputation: 528
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I don't know about VDSL, but at least in ADSL I believe that the PPP tunnel isn't actually terminated at the ISP – it only goes as far as the DSLAM station (a few meters to ~1 km away), so that might provide some clues. (Currently I'm trying to make sense of this document.)
– user1686 – 2018-06-11T10:03:07.8271@grawity A big reason the DSL industry kept PPP around (as PPPoE and PPPoA) was so the DSLAM POP operators could tunnel those customer sessions via L2TP to the ISPs’ PPP servers just like they did from dial-up modem pool POPs in the 1990’s. So the PPP session usually terminates at your ISP, not at whoever owns the DSLAM. – Spiff – 2018-06-11T15:46:07.957