Last Call Review of draft-ietf-mpls-rfc4379bis-07
review-ietf-mpls-rfc4379bis-07-genart-lc-davies-2016-10-18-00
| Request | Review of | draft-ietf-mpls-rfc4379bis |
|---|---|---|
| Requested revision | No specific revision (document currently at 09) | |
| Type | Last Call Review | |
| Team | General Area Review Team (Gen-ART) (genart) | |
| Deadline | 2016-10-18 | |
| Requested | 2016-10-06 | |
| Authors | Kireeti Kompella , George Swallow , Carlos Pignataro , Nagendra Kumar Nainar , Sam Aldrin , Mach Chen | |
| Draft last updated | 2016-10-18 | |
| Completed reviews |
Genart Last Call review of -07
by
Elwyn B. Davies
(diff)
Genart Telechat review of -07 by Elwyn B. Davies (diff) Secdir Last Call review of -07 by Vincent Roca (diff) Opsdir Last Call review of -07 by Sheng Jiang (diff) Rtgdir Early review of -06 by Daniele Ceccarelli (diff) |
|
| Assignment | Reviewer | Elwyn B. Davies |
| State | Completed | |
| Review |
review-ietf-mpls-rfc4379bis-07-genart-lc-davies-2016-10-18
|
|
| Reviewed revision | 07 (document currently at 09) | |
| Result | Not Ready | |
| Completed | 2016-10-18 |
review-ietf-mpls-rfc4379bis-07-genart-lc-davies-2016-10-18-00
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.
[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.
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.
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.
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.
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.
Nits/editorial comments:
======================
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.
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
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
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
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.
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
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
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')?
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.
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)
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
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.
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).
s3.2.9: s/sender's PE IPv4 address/Sender's PE IPv4 Address/;
s/remote PE IPv4 address/Remote PE IPv4 Address/
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.
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
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
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.
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.
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.
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.