[Gen-art] Post-Telechat update (was Re: Gen-art LC review of draft-ietf-mpls-rfc4379bis-07)

[Elwyn Davies <[e-mail]>]

Hi Carlos,

:-)
Thanks for addressing the comments.  I have looked through -08 and there 
are a couple of extra points that I noticed - the s3.4 issue was 
effectively mentioned wrt s4.5 in my previous notes.

Generally things are in good shape but there are some items that haven't 
been addressed or there is a quibble.

If there is another version over the weekend I'll do my very best to 
check it before Monday.

Regards,
Elwyn

Extra Points:
===========

I Forgot to mention that there is lack of consistency in capitalisation 
of the message names: Personally I would go with Echo Request and Echo 
Reply throughout to make it clear that these are message names.

s3,4, para 1:
> If the
>     replying router is the destination (Label Edge Router) of the FEC,
>     then a Downstream Detailed Mapping TLV SHOULD NOT be included in the
>     MPLS echo reply.  Otherwise, the replying router SHOULD include a
>     Downstream Detailed Mapping object for each interface over which this
>     FEC could be forwarded.
I suspect that the SHOULD NOT ought to be MUST NOT.  Otherwise it needs 
an explanation of the circumstances in which the DDMAP TLV could be 
included.  Similarly, the SHOULD needs to explain in what circumstances 
you wouldn't include one or more DDMAP TLVs.

s6.2.3: The Unassigned row should have a blank reference.

On 28/10/2016 02:29, Carlos Pignataro (cpignata) wrote:
> 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 <[e-mail] 
>> <mailto:[e-mail]>> 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>.
>>
>> 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.
Looks good to me!
>
>> [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.
There is one place (s3.1, para 1) where I think it could be made 
clearer.  Adding a few words to that section will help overall as well 
as just in that section.
>
>>
>> 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.
>
OK
>>
>> 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.
Fine.
>
>
>> 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 :-)
I think a short note in s3.5 about why it might be present would be 
useful. e.g.,
        The Pad TLV can be added to an Echo Request to create a message 
of a specific length
        in cases where pings of various sizes are needed for 
troubleshooting.
>
>> Nits/editorial comments:
>> ======================
>
> Thank for for these. Unless I make a specific follow-up inline, the 
> nit is fixed.
There are a couple of places where this doesn't seem to be the case, 
especially in a number of places where there are SHOULDs in the text but 
the reasons for/consequences of not following the SHOULD are not spelt 
out.  This can be important for interoperability.
>
>> 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
That's OK by me.  I wondered whether the DDM in the return code had been 
too firmly ensconced to change.
>
>>
>> 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.
This didn't happen.  Not essential but useful.
>>
>> 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.
Fair enough.
>
>>
>> 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"
OK
>
>> 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.
I just realized that the draft doesn't say that the Sequence Number is 
also (I assume) returned unchanged in the Echo Reply.  To emphasize this 
copying, it would probably be good to use the MUST word about both 
request -> reply copies.
>
>> 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”.
Yes.. oops.
>
>> 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.
OK
>
>> 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..
Fine.  I was just wondering.
>
>> 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.
True!
>
> As part of this, I also cleaned up all the “[sub][-]section” citations.
Good.
>
>>
>> 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.
The market may go down as well as up!  I'll have to live with this.
>
>> 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.
Hmm.  I found this potentially confusing.  This was the main point at 
which I thought the use of sender and receiver needed clarifying.  Am I 
right in thinking that the 'sender' is always the node sending an Echo 
Request and the 'receiver' is a node that is triggered by the Echo 
Request to send an 'Echo Reply'.  The issue for me is that the receiver 
also sends messages.  How about:
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 is set to zero in the Echo Request message by the 
(Echo Request) sender.
    The ((Echo Request) receiver can set it to one of the values listed 
below in the corresponding
     Echo Reply that it generates.
END
It is possible that I am misinterpreting sender or receiver.. but if so 
I would say that some additional words would help.
>
>> 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.
Thew new text is fine.
>
>>
>> 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.)
This didn't happen.

>>
>> 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.
Wild!
>
>> 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),
OK.  I think I read the text incorrectly here.  On reflection it looks 
fine as is.
>
>> 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?
This hasn't been addressed AFAICS.
>>
>> 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).
Ah!  Actually the original text and what I wrote are both wrong! The 
text in -08 is arguably not wrong, but is confusing because it looks 
like the instructions for Return Code.
VERSION 08 TEXT:
       The Return Subcode is set to zero by the sender.  The receiver can
       set it to an appropriate value as specified in Section 3.1. This
       field is filled in with the stack-depth for those codes that
       specify the stack-depth.  For all other codes, the Return Subcode
       MUST be set to zero.
MORE NEWER:
       The Return Subcode is set to zero by the sender.  The receiver 
can [MUST?]
       fill this field with the stack-depth for those codes that
       specify the stack-depth as indicated in Section 3.1  For all 
other codes, the Return Subcode
       MUST be set to zero.

>
>> 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.
Octets: good.  I'll live with the rest.
>
>> 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?
Thinking about this some more, I see these aren't operation rules in the 
same sense as s4 uses operation.  They are actually ordering rules:
OLD:
    FEC stack change sub-TLV operation rules are as follows:
NEW:
    When a DDMAP TLV needs several FEC stack change sub-TLVs to record 
the changes
    that the LSR makes to the label stack, the following number and 
ordering rules MUST
    be respected:
END

>>
>> 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.
See comment on s3.4 at head of message.
>>
>> 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.
OK
>
>> 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.
I was thinking of whether (e.g.) having a RA option set in a packet 
other than a MPLS Echo Request/Response could be a way of doing a DoS 
attack on an MPLS network since it could overload the data->control 
plane link... might wish to filter any packets with RA set at ingress to 
MPLS network.  Not sure if the UDP port rate limit would help with this.
>
>>
>> s5, Security risks of DoS using Errored TLV?
Injecting MPLS Ping packets with bad TLVs could be a way of creating a 
DoS perhaps as it would produce Errored TLV messages.
>>
>> 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.