draft-ietf-6man-udpchecksums-02.txt

[Gorry Fairhurst <[e-mail]>]

Marshall &  Philip, I've read the new draft, and have a few new 
comments. Hope these are helpful - happy to discuss if this seems useful.

Best wishes,

Gorry

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BOILER PLATE:
- Please an Updates line:goprry
"Updates RFC2460 (if approved)"

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Section 3:
   "there is no additional
    benefit and indeed some cost to nodes to both compute and check the
    UDP checksum of the outer (encapsulating) header."

- I do not think this sentence is really true, and I think it's
important that we do get this right. I suggest there ARE benefits in
performing a UDP integrity check for IPv6, see Section 3 of
I-D.ietf-6man-udpzero. However, I agree that omitting this check can
reduce the forwarding cost for systems that perform the check in software.

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Section 3:
   "to set the checksum field of the
    outer header only to 0 and skip both the sender and receiver
    computation."

- Could we insert a "UDP transport" between "outer" and "header" above,
so there can be no confusion with the network layer headers.

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Section 4:
    "In Section 5.1 of [I-D.ietf-6man-udpzero], the authors propose nine
    (9) constraints on the usage of a zero checksum for UDP over IPv6.
    We agree with the restrictions proposed, and in fact proposed some of
    those restrictions ourselves in the previous version of the current
    draft.  These restrictions are incorporated into the proposed changes
    below."

- This reads rather like a paper. ietf-6man-udpzero is also a working
group document, and I would like to think we can find better language.
I suggest something like:

    "Section 5.1 of [I-D.ietf-6man-udpzero], identifies 9 requirements
    that introduce constraints on the usage of a zero checksum for
    UDP over IPv6. This document is intended to satisfy these
    requirements."

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Section 4:
  "inspection firewall devices or other middleboxes actually checking"
- remove "actually"?

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Section 4:
   "This is would be an issue also for legacy systems
    which have not implemented the change in the IPv6 specification.  So
    in any case, there may be packet loss of lightweight tunneling
    packets because of mixed new-rule and old-rule nodes."

- Seems like it could be improved. I suggest:
   "This would be an issue also for any legacy IPv6 system
    that has not implemented the change to the IPv6 specification. In
    this case, the system will discard the zero-checksum UDP
    packets, and should log this as an error."

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Section 4:
"   As an example, we discuss how can errors be detected and "
                                   ^^^
- remove "can"

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Section 4:
   "Note that other (non-tunneling) protocols may have
    different approaches."
- suggest replace add:
   ", but these are not the topic of this update."

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Section 4:
   "The control packets can
    also contain any negotiation that is necessary to set up the
    endpoint/adapters to accept UDP packets with a zero checksum."
- this needs to be enabled for each flow, so please add:
"The control packets may
       also carry any negotiation that is necessary to set up the
       endpoint/adapters to identify the set of ports that
       need to enable reception UDP datagrams with a zero
        checksum."

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Section 4:
"Only UDP packets containing tunneled packets should have a UDP
       checksum equal to zero."
- Please use keywords. e.g.
  "A system MUST NOT set the UDP checksum to zero in packets that do
not contain tunneled packets."

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Section 4:
"We note that
       these outcomes not equally likely, as most require multiple bit
       errors with errored bits in separate fields. "
- It seems wrong to suggest that single bit inversions are a likely
cause of residual errors at the transport layer. I do not think this is
the case. I suggest direct replacement of a sequence of bytes is a
likely form of corruption. Suggest you omit the second part of the sentence?

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Section 4:
" If it is some
          other application, with very high probability, the application
          will not recognize the contents of the packet."
- I disagree - it all comes down to applications design. The detection
is only if the app is defined this way, since the transport does not
know, etc. RFC 5405 provides recommended best current practice for
applications in general.

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Section 4:
- I think the wording of this section needs to be tightened.It would be
good to see more of a focus on what needs to be implemented, rather than
discussing the guidance provided in the other working group document.

If the guidance itself needs to be updated, then it would be good to
explore this - We'd be happy to update the text and guidance if there is
something more that should be said.

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Section 5:
"   outer encapsulating packet of a lightweight tunneling protocol."
- is it intentional to permit this only for *lightweight* tunneling
protocols? - The initial request was for *any* tunneling protocol that
meets the requirements.

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Section 5:
"UDP
    endpoints that implement this solution MUST change their behavior and
    not discard UDP packets received with a 0 checksum on the outer
    packet of tunneling protocols."
- I think we really should add a few words about being enabled only for
the set of ports that are supported by system for use by tunneling
protocol(s).

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Section 5:
"its behavior should be as specified originally."
- replace "should be as specified originally", by "is not updated and
uses the method specified in RFC2460".

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Section 6:
"   The persistence of this issue among a significant number of
protocols being developed in the IETF requires a definitive policy."
- Is this a recommendation for more work, or a statement of the
motivation for this document. I was not sure.

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Section 6:
- I think it could be useful to include the points in section 6 possibly
also as a part of ietf-6man-udpzero. What do you think?


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I'd suggest we add a normative citation to RFC 5405, stating that this
provides the IETF guidance on the design of applications using UDP and
includes guidelines on the usage of checksums by application designers.

- Possibly best placed in the introduction, indicating that this
document adds to this for the case of tunneling applications.

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-- 
Prof Gorry Fairhurst, School of Engineering, University of Aberdeen.
The University of Aberdeen is a charity registered in Scotland,
No SC013683.