I am the assigned Gen-ART reviewer for this draft. For background on Gen-ART, please see the FAQ at < http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>. Please wait for direction from your document shepherd or AD before posting a new version of the draft. Document: draft-ietf-mpls-tp-psc-itu-03.txt Reviewer: Elwyn Davies Review Date: 22 March 2014 IETF LC End Date: 2014-02-24 IESG Telechat date: 27 March 2014 Summary: Almost ready. There are a couple of points which I raised at Last Call and discussed with the authors and others both by email and f2f in London that are not resolved. These point revolve around being rigorous about wire encoding, clarifying error behaviour and being definite that implementations support modes as specfic combinations of capabilities so that arbitrary capability combinations are not allowed and result in invalid protocol messages. Major Issues: Minor Issues: s1: From my discussions with the authors and others associated with this document, it is my understanding that the intention is that only combinations of capabilities specified by modes should be legal and hence that implementations would support modes rather than arbitrary sets of capbilities. I think it would be worth being more explicit about this. This would answer my comments at Last Call that it was unclear whether other combinations were allowed and would make it clear that a message that arrived with a corrupted bit in the flags field was definitely malformed. I suggest adding the following text to para 16 of s1 (starts "This document introduces capabilities and modes.") before the last sentence: Only combinations of capabilities specified by modes will be supported by implementations. Nits/Editorial Comments: s4.4, para 1: OLD: When the modified priorities specified in this document is in use,.. NEW: When the modified priorities specified in this document are in use,.. (or maybe better:) When the modified priority order specified in this document is in use,.. s7.3 et seq: The term "selector bridge" is introduced without definition. I suspect it is a piece of jargon I am supposed to know but I think a reference would help. s9.1: RFC 6378 doesn't define the encoding of the TLV type and TLV length fields, so it needs to be done here (Unsigned integers). It also doesn't define encoding of the overall TLV length field in the PSC header. This may be thought to be 'obvious' but there is no default specified in IETF documents. s9.1: Both RFC6378 and this document are incomplete as regards specifying what constitutes an invalid protocol message. In particular there is no discussion of behaviour if correctly formed but unrecognized TLVs are received. Do these make the message invalid or should they be ignored? s9.1.1 and s12: In s12 it is stated (similar wording in s9.1.1): > o If the Capabilities TLV mismatches, the node MUST alert the > operator and MUST NOT perform any protection switching until the > operator resolves the mismatch in the Capabilities TLV. Having discussed the situation with the authors and others, I understand that there are circumstances, depending on the underlying transport, that bit errors might not be detected and hence that there is a small probability that corrupt PSC messages may be propagated up to the protocol machine. At present there is no explicit statement that a corrupted flag word would be trapped as an invalid protocol message (this seems to be the intention) rather than triggering this operator alert. I think that the best that can be done is specify that a PSC protocol message MUST have the flags for a recognized mode set exactly and otherwise it will be treated as an invalid message. The wording in s9.1.1 and s12 would then catch an inadvertent reconfiguration. I suggest adding the following to s9.1.1: Any PSC message that has a combination of capability bits set that does not correspond to a defined mode will be treated as an invalid message and ignored.