[Sipping] draft-campen-sipping-stack-loop-detect-00, top route headers and spiraling

Both draft-campen-sipping-stack-loop-detect-00 and RFC3261 include the topmost Route header in the calculation of a digest for loop detection. This will fail in the following scenario involving a UE and 3 proxies P1,P2,P3:

UE sends:
INVITE U1
Route: P1

P1 removes Route: P1 and forwards to P2:
INVITE U1
Route: P2

P2 removes Route: P2 and forwards to P3 via P1:
INVITE U1
Route: P1, P3

P1 receives this request and detects a loop (while it shouldn't).

In other words, the route header that influences the processing is the topmost Route header *after* removing route headers that point to the element processing the request. In terms of RFC3261, the processing step mentioned at the end of section 16.4 should be performed before section 16.3 point 4.

Second issue: the loop-detect-draft suggest the use of an IP address to identify a node. This won't work in case multiple ports and/or transports are used at a single IP address. Each should be treated as a different logical instance of a proxy (hence: suggestion to include the transport and port in the node identifier)

Final question: do I understand correctly that the stack-based loop detection algorithm may detect a multi-hop loop later than the current RFC3261 algorithm? So if I have UE->P1->P2->P3->P1->P2 it may detect it at P2, not P1?

Regards,

Jeroen