Deal Elwyn, Many thanks for a great review!
I just finished addressing all your comments: the major issue (easy to address, editorial fix, but with important implications), the minors, and all the nits. Surprisingly, I found a few small additional editorials, which I fixed as well. Rev -08 would address all outstanding issues, from this review, Mirja, and a couple others. Please see inline for a line-by-line set of responses. On Oct 20, 2016, at 4:42 PM, Elwyn Davies <[email protected]<mailto:[email protected]>> wrote: I am the assigned Gen-ART reviewer for this draft. The General Area Review Team (Gen-ART) reviews all IETF documents being processed by the IESG for the IETF Chair. Please treat these comments just like any other last call comments. For more information, please see the FAQ at <http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq><http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>. Document: draft-ietf-mpls-rfc4379bis-07.txt Reviewer: Elwyn Davies Review Date: 2016/10/21 IETF LC End Date: 2016/10/18 IESG Telechat date: (if known) - Summary: Not ready. There is one major issue (already notified to authors and agreed as an issue) and a considerable number of minor and editorial issues. I have worked through the various RFCs and errata that are subsumed into the new version and almost everything has been correctly translated AFAICS. A couple of minor points are covered in the comments. Major issues: ============ s3.4: A number of items that are used in the normative Downstream Detailed Mapping TLV were originally defined in s3.3 (Downstream Mapping TLV format) but have been shifted to Appendix A.2. This appendix is marked as non-normative. Thus there are now no normative definitions for the various TLVs used in s3.4 that are defined in A.2. I fear that these need to be returned to the normative part of the specification. This is an excellent catch. Thank you. The fix is simple and purely editorial but the implication is clear. I finished addressing this, which you will see posted as the new revision. I am super happy with the outcome. [I think it would be simplest and least error prone to swap the text that was in s3.3 of RFC 4379 back out of A.2 and put backward references to the new s3.4 into A.2 as necessary.] Minor issues: ============ Sender/receiver terminology: The document can be somewhat confusing to a naive reader. Sender and receiver are used in multiple contexts. Where the context appears to relate to LSP ping, both senders and receivers are involved in sending LSP ping packets. In general, sender and receiver appear to imply sending and receiving of Echo Request messages with their roles reversed with respect to Echo Responses, with the receiver stimulated to send an Echo Response by receiving an Echo Request. It would help if this terminology and usage was explicitly set out early in the document. Additionally, some instances would be made more comprehensible by making the function explicit in the text e.g., in the operation of return codes. Re-reading after fixing all the nits below, which include some sender clarifications, looks good. s1.4/s3/s6.2.3: The R (Global) flag is defined in RFC 6426. Unfortunately it isn't in the IANA considerations there as was spotted in RFC Erratum 4012. Might be worth mentioning the erratum (probably in s1.4?) Alternatively this document can be made to provide the IANA specification for the R flag and the erratum closed. The WG decided to keep the definition of the R Flag in RFC 6426 and not here — consequently, there’s little that can really be done as the erratum (which really is symbolic since the IANA registry is fixed) applies to RFC 6426 and not to RFC 4379. s2.1/s6: An update to http://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml is needed to replace RFC 4379 with RFC-to-be for special exceptions to usage rules. Done. s3.5, Clandestine Channel via Pad TLV: As specified the value part of a Pad TLV can serve as a clandestine channel since the value field contents are ignored. Added the following to S5: The value part of the Pad TLV contains a variable number of octets. With the exception of the first octet, these contents, if any, are ignored on receipt, and can therefore serve as a clandestine channel. s3.5, Usefulness of Pad TLV: Could you explain circumstances in which a Pad TLV would be needed please. I can't see any at present. Sure — when you want to send pings of various sizes for troubleshooting. I’ve used it in productions :-) Nits/editorial comments: ====================== Thank for for these. Unless I make a specific follow-up inline, the nit is fixed. General: s/i.e. /i.e., / (two instances s3.2, last para; s4.5.1, para 3) s1, para 1: s/methods of reliable reply/methods of providing reliable reply/ s1.4, bullet 4: Need to expand acronym PW on first use. s1.4, bullet 4: need to move expansion of FEC acronym to here from s2. s1.4, bullet 8: Acronyms DSMAP/DDMAP: When defining Return Code 14 in s3.1, the text is 'See DDM TLV...'. DDM is not expanded anywhere although it is clearly the same as DDMAP. But has by now made it into the IANA repository and is probably better to use it for 'Downstream Detailed Mapping', so I suggest: OLD: o Incorporate the updates from RFC 6424, by deprecating the Downstream Mapping TLV (DSMAP) and adding the Downstream Detailed Mapping TLV (DDMAP), updating two new return codes, updating the procedures, IANA section, Security Considerations, and obsoleting RFC 6424. NEW: o Incorporate the updates from RFC 6424, by deprecating the Downstream Mapping TLV (DSM) and adding the Downstream Detailed Mapping TLV (DDM), adding two new return codes, updating the procedures, IANA section, Security Considerations, and obsoleting RFC 6424. END Then s/DSMAP/DSM/g, s/DDMAP/DDM/g in the rest of the document. This is a good point, where DDM came from RFC 6424. However, these fields are known as DSMAP and DDMAP. Consequently, global replacing DDM -> DDMAP s1.4: Ought to mention the addition of the motivation (LSP stitching) for the additions in RFC 6424. s2.1, paras 7 and 8: This contains "the newly designated IPv4 link local addresses". Given that RFC 3927 is now over 11 years old, the qualifier is no longer appropriate, but it might be useful to provide a ref. Thus: OLD: the newly designated IPv4 link local addresses NEW: the IPv4 link local addresses [RFC3927] END The text in para 8 is also no longer appropriate. Suggest OLD: Furthermore, the IPv4 link local address range has only recently been allocated. Many deployed routers would forward a packet with an address from that range toward the default route. NEW: Older deployed routers may not correctly implement link local addresses and would forward a packet with an address from that range toward the default route. END Yes, many thanks. Updated with a slight change “Older deployed routers may not (correctly) implement IPv4 link local addresses …" s2.1, para 9: s/embedded in as/embedded in an/ s2.1, para 9: Useful to add a reference to RFC 4291. s2.2, para 1: To be clearer about the distinction between IPv4 and IPv6, suggest: OLD: This document requires the use of the Router Alert Option (RAO) set in IP header in order to have the transit node process the MPLS OAM payload. NEW: This document requires that the Router Alert Option (RAO) is carried in the IP header in order to have the transit node process the MPLS OAM payload. For IPv4 packets the RAO [RFC2111] MUST be added to the IPv4 header; for IPv6 packets a hop-by-hop RAO [RFC2711] must be chained to the IPv6 header. END I wanted to keep that paragraph IP version agnostic, since the specifics for IPv4 and IPv6 come in the next two paragraphs. s3, para 1: An MPLS echo request is a (possibly labeled) IPv4 or IPv6 UDP packet; This format applies to both requests and responses but the response case is not made explicit. Suggest: OLD: An MPLS echo request is a (possibly labeled) IPv4 or IPv6 UDP packet; NEW: An MPLS LSP ping message, is a (possibly labeled) IPv4 or IPv6 UDP packet; END That would leave out “traceroute” mode. I’ll add “request/reply" s3, main packet format and associated text: The Sender's Handle is not the packet sender's handle but the Echo Request Sender's Handle - it is copied in to the corresponding Echo Reply. Suggest renaming the Sender's Handle and Sequence Number to Echo Request Sender's Handle and Echo Request Sequence Number. This would affect para 5 of s4.3, para 2 of s4.5 and para 1 of s4.6 also. That would be too big of a departure for very well-known fields. s3, Timestamp format: RFC 5905 allows for 3 different time formats - the 32 bit basic format is intended: OLD: The TimeStamp Sent is the time-of-day (according to the sender's clock) in NTP format [RFC5905] NEW: The TimeStamp Sent is the time-of-day (according to the sender's clock) in 32 bit NTP format [RFC5905] END 64-bit. I changed to “64-bit NTP Timestamp format”. s3, Global flags: Technically, this doc only defines the V flag: Also forcing the other bits to be zero restricts addition of new flags> OLD: This document defines three flags, the R, T, and V bits; the rest MUST be set to zero when sending and ignored on receipt. NEW: At the time of writing three flags are defined, the R, T, and V bits; the rest SHOULD be set to zero when sending and ignored on receipt. END I changed the first part but leave in the MBZ. s3, TLV types: The values 4, 6 and 8 for TLV type and the value 5 for Tthe sub-type of TLV type 1 are specified as 'Not assigned': To be clear for the future, should these really be marked as 'Reserved' or could they be assigned in future (and hence s/b marked as 'Available for assignment')? They are not assigned. IANA now calls these as Not Assigned as “Unassigned” — updated.. s3: For clarity it would be useful to add a sentence to the end of the section stating: In Sections 3.2 - 3.4 and their various sub-sections, only the value section of the TLV is specified. Sure. But it’s really from 3.2 through 3.9. As part of this, I also cleaned up all the “[sub][-]section” citations. s3, TLV length calculation: This is shown by example only. I think it ought to be explained explicitly in text. I suggest: The length of a sub-TLV or a TLV whose value is not a list of sub-TLVs is the number of significant octets in the value part of the (sub-)TLV excluding any final padding. If the value of a TLV is a list of sub-TLVs, the length of the TLV is the sum of the overall lengths of the sub-TLVs including the sub-TLV header and the length of the padding, i.e. 4 + ((sub-TLV.length + 4) mod 4) The examples are clear enough and have been clear throughout many implementations. s3.1, para 1: I think this should be interpreted as saying that the Return Code MUST always be zero in an Echo Request and the Return Code is set to an appropriate one of the possible values in an Echo Reply. To be clear: I take it that it would not be normal for an Echo Reply to carry a zero Return Code. Assuming this is right... OLD: The Return Code is set to zero by the sender. The receiver can set it to one of the values listed below. NEW: The Return Code MUST be set to zero in an Echo Request message. The responder sets the Return Code in the Echo Reply message to an appropriate value other then zero from the list below. END Current text is OK. s3.1, Return code 14: Some of the extra text from Section 3.2.1 of RFC 6424 ought to be essential as it contains 'MUSTS'. Suggest adding this as an extra note against Return Code 14: Note 2: Return Code 14 is used to indicate that an Echo Reply contains one or more DDM TLVs (see Section 3.4). In this case there will be one Return Code and corresponding <RSC> for each path described and these are passed in the DDM TLV(s). This Return Code MUST only be used in the Echo Reply message header and MUST NOT be used in the Echo Request message even if the message contains a DDM TLV. Sure, added different text (above is incorrect), but this is a really good point. Updated also a section citation to point to this note. s3.1: The term IS_EGRESS is used later in the document to indicate an Echo Reply message with a Return Code of 3. It should defined here. The meaning is fairly obvious at its first use in s3.4(e) but there is not a formal definition. (AFAICS textual acronyms are not used for any of the other codes.) s3.2, last but one para: s/previx/prefix/ s3.2.8/s3.2.9/s3.2.11: It would be useful to use the name of the FEC type from RFC 4447 (PWid FEC) rather than just its number. (Also in A.1.1). The names are wildly used, and citations to 4447 exist. I’ll leave it as is. s3.2.9: s/sender's PE IPv4 address/Sender's PE IPv4 Address/; s/remote PE IPv4 address/Remote PE IPv4 Address/ OK, same for the Appendix and IPv6 PE addresses. s3.2.9, para 3: Need to expand PE acronym on first use. s3.2.10, para 1: The text uses source PE IPv4 address whereas the diagram uses Sender's PE IPv4 Address. Consistency is needed. See also the previous comment regarding consistency and capitalization. This is explained: Sender's Provider Edge (PE) IPv4 Address (the source address of the targeted LDP session), s3.2.10/s3.2.12: : It would be useful to use the name of the FEC type from RFC 4447 (Generalized PWid FEC) rather than just its number. s3.2.12: The text uses source whereas the diagram and field name use Sender's... consistency again? s3.4, DS Flags: I Interface and Label Stack Object Request When this flag is set, it indicates that the replying router SHOULD include an Interface and Label Stack Object in the echo reply message. What circumstances would cause the replaying router not to do this? What should it do otherwise? s3.4, Return Code: The Return Code is set to zero by the sender. The receiver can set it to one of the values specified in the "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters" registry, "Return Codes" sub-registry. a) I suspect that in the basic LSP ping described in this document, the return codes that ought to be available are only those specified in s3.1 of this document except for 14 (which is specifically only allowed in the header). The registry now contains a number of other return code values but a basic implementation wouldn't understand them in general. b) See the previous comments on meaning of sender and receiver. Suggest: OLD: The Return Subcode is set to zero by the sender. The receiver can set it to one of the values specified in the "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters" registry, "Return Codes" sub-registry. NEW: The Return Code in the (one) DMM TLV in an Echo Request message MUST be set to zero. The responder sets the Return Code in any DMM TLV in the Echo Reply message to an appropriate value other then zero or 14 ("See DDM TLV for Return Code and Return Subcode") taken from the list in Section 3.1. END Similar issue with the Subcode (you are mixing RC with RSC in the OLD/NEW). s3.4, Sub-tlv Length: I think that the components of the DSM are all multiples of 4 octets long so there is no padding to consider (apart from possibly in FECs ). OLD: Total length in bytes of the sub-TLVs associated with this TLV. NEW: Total length in octets of the sub-TLVs associated with this TLV including the TLV headers and any padding. END Leaving this does not hurt — however, fixed the bytes -> octets throughout. s3.4.1.3, FEC TLV length: Does this include any trailing padding and the TLV header? s3.4.1.3, Operation Rules: Shouldn't these be in s4? s3.6: Should contain a reference to the IANA registry URL. Sure, why not :-) s4.1, last para: s/some information how each/some information as to how each/ s4.2: s/to differentiate whether/to ascertain whether/ s4.3, para 1: s/MUST be set in IP header/MUST be set in appropriate IP options/ s4.4, item 1: It would be helpful to remind implementers how TLVs are marked to be ignored: OLD: If there are any TLVs not marked as "Ignore" NEW: If there are any TLVs not marked as "Ignore" (i.e., if the TLV type is less than 32768, see Section 3) END s4.4: s/subsection/Section/g s4.4, item 3: s/If there is no entry for L {/If there is no entry for Label-L {/ s4.4, item 4: OLD: Set Best-return-code to Return Code 9, "Label switched but no MPLS forwarding at stack-depth" and set Best-rtn- subcode to Label-stack-depth and goto Send_Reply_Packet. NEW: Set Best-return-code to Return Code 9, "Label switched but no MPLS forwarding at stack-depth" and set Best-rtn- subcode to Label-stack-depth and goto step 7 (Send Reply Packet). END s4.4.1, item 5: s/advertise FEC/advertise the FEC/ s4.5: If the replying router is the destination of the FEC, then Downstream Detailed Mapping TLVs SHOULD NOT be included in the echo reply. Under what circumstances might one be included? I think this is a MUST NOT. s4.5.2: This section is derived from s4.1.2 of RFC 6424. Whilst the new version appears to contain sufficient to define the proper normative behaviour, RFC 6424 contains additional examples of usage. These look useful to me. I wonder if it might be useful either to copy the illustrative material to an appendix or maybe point back to RFC 6424. I am not sure how the powers-that-be would consider back pointers to obsoleted documents! Maybe something like: [RFC6242] which originally specified the techniques needed to support tunnel transition contains some examples, in Section 4.1.2, of situations where the technique would be applied. This was discussed and decided did not want to over copy when the current text is enough. s4.6: If the echo reply contains Downstream Detailed Mappings, and X wishes to traceroute further, it SHOULD copy the Downstream Detailed Mapping(s) into its next echo request(s) (with TTL incremented by one). Presumably this means one DMM per Echo Request... might be worth being more explicit. s5: Security risks of Router Alert. Mention RFC 6398 and maybe copy 2nd para of s6 of RFC 7506. I believe the RA usage (which is specific and not generic) is adequately covered. s5, Security risks of DoS using Errored TLV? s6: Given the responses from IANA, a note is needed to say that entries originated other than from RFC 4379 should remain unaltered in the registry. The only exception might be the R flag in Global Flags where it might be sensible to use this document to fix erratum 4012. s6.2.5, last line: Remove ']]' which appears to be spurious. s8: Several new references are mentioned in these comments and would need to be added if the suggestions are actioned. Very many thanks again for the review! — Carlos.
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