Symptom
Following tracebacks may be seen:
002529: Nov 28 10:53:45.898 UTC: L2TP-3-ILLEGAL _____:_____:________:
ERROR: L2TP session, no L2X
-Traceback= 1#fa53c8e50eb34ad6b14c6e73742aa633 :400000+8D10D1
:400000+36F9F5C :400000+36F9D22 :400000+36F9AFA :400000+371DAF0
:400000+3721419 :400000+370EFE7 :400000+370EF7B :400000+3713909
:400000+3713639 :400000+3714FC5 :400000+37165DF :400000+3717003
:400000+3717F11 :400000+3714CF3 :400000+36FAEB4
002530: Nov 28 10:53:45.900 UTC: L2TP-3-ILLEGAL _____:_____:________:
ERROR: L2TP session, no L2X
-Traceback= 1#fa53c8e50eb34ad6b14c6e73742aa633 :400000+8D10D1
:400000+36F9F5C :400000+36F9D22 :400000+36F9AFA :400000+371DAF0
:400000+371ED59 :400000+3720AFE :400000+370EF94 :400000+3713909
:400000+3713639 :400000+3714FC5 :400000+37165DF :400000+3717003
:400000+3717F11 :400000+3714CF3 :400000+36FAEB4
002531: Nov 28 10:53:45.902 UTC: L2TP-3-ILLEGAL _____:_____:________:
ERROR: unexpected
-Traceback= 1#fa53c8e50eb34ad6b14c6e73742aa633 :400000+8D10D1
:400000+36F9F5C :400000+36F9D22 :400000+36F9AFA :400000+3720B2B
:400000+370EF94 :400000+3713909 :400000+3713639 :400000+3714FC5
:400000+37165DF :400000+3717003 :400000+3717F11 :400000+3714CF3
:400000+36FAEB4 :400000+3714E83 :400000+3716B29
Root cause is L2TP sessions being torn down at the moment the session is being renegotiated.
--> This is a very corner case and should remain very rare.
Tracebacks are harmless in this case. (As the L2TP session was being torn down anyway)