ICMP Attacks against TCP
draft-ietf-tcpm-icmp-attacks-12

[Ballot comment]
This document should be approved as an RFC. Thanks for
writing it.

However, I would like to note the following text from the document:

  The consensus of the TCPM WG (TCP Maintenance and
  Minor Extensions Working Group) was to document this widespread
  implementation of nonstandard TCP behavior but to not change the TCP
  standard.

This would seem to imply that the TCPM WG has decided to deviate
from the old IETF operating principle of "rough consensus and
running code". For at least some of the techniques described in
this draft, they are generally accepted and widely implemented
on key implementations. I ask what the reason is for divorcing
IETF standards from established best practices and actual running
code?

[Ballot comment]
section 7.3.2, figure 3 line 2: DATA size should be 1460, not 1500 (established MTU is 1500)

Section 7.3.5, figure 6 line 8: for this example, shouldn't TCPseq#=201 or 301?  101 has
already been acknowledged...

[Ballot discuss]
This document does an admirable job of articulating the important reasons that many tcp
stacks implement these features.  However, there is a downside; a stack might not react to
a valid ICMP that happened to be delayed in the network, or react more slowly to a valid
ICMP. For completeness, I would like to see a brief discussion of the reasons one might
choose not to implement these features.  Nothing too long, simply enough to acknowledge
the complexities of the topic.

[Ballot comment]
section 7.3.2, figure 3 line 2: DATA size should be 1460, not 1500 (established MTU is 1500)

Section 7.3.5, figure 6 line 8: for this example, shouldn't TCPseq#=201 or 301?  101 has
already been acknowledged...

[Ballot discuss]
This document does an admirable job of articulating the important reasons that many tcp
stacks implement these features.  However, there is a downside; a stack might not react to a valid ICMP that happened to be delayed in the network, or react more slowly to a valid ICMP. For completeness, I would like to see a brief discussion of the reasons one might choose not to implement these features.  Nothing too long, simply enough to acknowledge the complexities of the topic.

[Ballot comment]
Section 7.1:

For IPv6, the
  reported Next-Hop MTU could be as low as 1280 octets (the minimum
  IPv6 MTU) [RFC2460].

Actually the reported MTU can be lower than 1280. The proper response is to send if I understand RFC 2460 is to send a <= 1280 bytes packet with fragmentation header.

From section 5 of RFC 2460:

  In response to an IPv6 packet that is sent to an IPv4 destination
  (i.e., a packet that undergoes translation from IPv6 to IPv4), the
  originating IPv6 node may receive an ICMP Packet Too Big message
  reporting a Next-Hop MTU less than 1280.  In that case, the IPv6 node
  is not required to reduce the size of subsequent packets to less than
  1280, but must include a Fragment header in those packets so that the
  IPv6-to-IPv4 translating router can obtain a suitable Identification
  value to use in resulting IPv4 fragments.  Note that this means the
  payload may have to be reduced to 1232 octets (1280 minus 40 for the
  IPv6 header and 8 for the Fragment header), and smaller still if
  additional extension headers are used.

[Ballot discuss]
I would like to discuss whether the following paragrah does not require more specific information:

>  Most of the these counter-measures can be implemented while still
  remaining compliant with the current specifications, as they simply
  describe reasons for not taking the advice provided in the
  specifications in terms of "SHOULDs", but still comply with the
  requirements stated as "MUSTs".

Why only 'most' and not 'all'? Which are the exceptions? I could not find anything in the counter-measures description excepting maybe the ambiguity in the specification about ICMP message type 3 code 3 described in 5.1 and 5.2. Are there other that I missed? Should not this be explained in a more detailed manner?

[Ballot comment]
section 7.3.2, figure 3 line 2: DATA size should be 1460, not 1500 (established MTU is 1500)

Section 7.3.5, figure 6 line 8: for this example, shouldn't TCPseq#=201 or 301?  101 has
already been acknowledged...

[Ballot discuss]
This is a discuss-discuss.

The working group summary in the IESG writeup states

  The WG did not reach consensus that the IETF
  should recommend the mitigation techniques documented in this
  document due to a number of associated drawbacks, although
  some of the these techniques are widely implemented in
  popular TCP stacks.

Perhaps I am missing something, but I did not see any documentation of the associated
drawbacks.  I think that is important for this document.  What do others think?

[Ballot discuss]
This is a discuss-discuss.

The working group summary states

  The WG did not reach consensus that the IETF
  should recommend the mitigation techniques documented in this
  document due to a number of associated drawbacks, although
  some of the these techniques are widely implemented in
  popular TCP stacks.

Perhaps I am missing something, but I did not see any documentation of the associated
drawbacks.  I think that is important for this document.  What do others think?

[Ballot comment]
section 7.3.2, figure 3 line 2: Data size should be 1460, not 1500 (established MTU is 1500)

The working group summary states

  The WG did not reach consensus that the IETF
  should recommend the mitigation techniques documented in this
  document due to a number of associated drawbacks, although
  some of the these techniques are widely implemented in
  popular TCP stacks.

Perhaps I am missing something, but I did not see any documentation of the associated
drawbacks.  I think that is important for this document.

draft-ietf-tcpm-icmp-attacks-09
 


  (1.a) Who is the Document Shepherd for this document? Has the
        Document Shepherd personally reviewed this version of the
        document and, in particular, does he or she believe this
        version is ready for forwarding to the IESG for publication?


Wesley Eddy (Wesley.M.Eddy@nasa.gov) is the document shepherd.  He
has personally reviewed this version and believes it is ready for
forwarding to the IESG for publication.



  (1.b) Has the document had adequate review both from key WG members
        and from key non-WG members? Does the Document Shepherd have
        any concerns about the depth or breadth of the reviews that
        have been performed? 


The document has had review in the TCPM working group; the shepherd
has no concerns about the depth or breadth of reviews performed.



  (1.c) Does the Document Shepherd have concerns that the document
        needs more review from a particular or broader perspective,
        e.g., security, operational complexity, someone familiar with
        AAA, internationalization or XML?

No.



  (1.d) Does the Document Shepherd have any specific concerns or
        issues with this document that the Responsible Area Director
        and/or the IESG should be aware of? For example, perhaps he
        or she is uncomfortable with certain parts of the document, or
        has concerns whether there really is a need for it. In any
        event, if the WG has discussed those issues and has indicated
        that it still wishes to advance the document, detail those
        concerns here. Has an IPR disclosure related to this document
        been filed? If so, please include a reference to the
        disclosure and summarize the WG discussion and conclusion on
        this issue.

No.



  (1.e) How solid is the WG consensus behind this document? Does it
        represent the strong concurrence of a few individuals, with
        others being silent, or does the WG as a whole understand and
        agree with it? 

There does not seem to be any opposition to this document in the working
group.  I believe it is understood by everyone; a large number of people
have evaluated it from both standards and implementation perspectives.



  (1.f) Has anyone threatened an appeal or otherwise indicated extreme
        discontent? If so, please summarise the areas of conflict in
        separate email messages to the Responsible Area Director. (It
        should be in a separate email because this questionnaire is
        entered into the ID Tracker.)

No.



  (1.g) Has the Document Shepherd personally verified that the
        document satisfies all ID nits? (See the Internet-Drafts Checklist
        and http://tools.ietf.org/tools/idnits/). Boilerplate checks are
        not enough; this check needs to be thorough. Has the document
        met all formal review criteria it needs to, such as the MIB
        Doctor, media type and URI type reviews?

One false nit found by IDnits is a non-RFC3330-compliant IPv4 address; this
is triggered by idnits thinking a sub-section numer reference is an IPv4
address.


  (1.h) Has the document split its references into normative and
        informative? Are there normative references to documents that
        are not ready for advancement or are otherwise in an unclear
        state? If such normative references exist, what is the
        strategy for their completion? Are there normative references
        that are downward references, as described in [RFC3967]? If
        so, list these downward references to support the Area
        Director in the Last Call procedure for them [RFC3967].

Yes; references are split into normative and infromative.  All normative
references are alrady published RFC documents, and since this is an
Informational document, none are downward references.



  (1.i) Has the Document Shepherd verified that the document IANA
        consideration section exists and is consistent with the body
        of the document? If the document specifies protocol
        extensions, are reservations requested in appropriate IANA
        registries? Are the IANA registries clearly identified? If
        the document creates a new registry, does it define the
        proposed initial contents of the registry and an allocation
        procedure for future registrations? Does it suggest a
        reasonable name for the new registry? See [RFC5226]. If the
        document describes an Expert Review process has Shepherd
        conferred with the Responsible Area Director so that the IESG
        can appoint the needed Expert during the IESG Evaluation?

The IANA considerations section exists; and there are no requests
being made of IANA for this document.



  (1.j) Has the Document Shepherd verified that sections of the
        document that are written in a formal language, such as XML
        code, BNF rules, MIB definitions, etc., validate correctly in
        an automated checker?

N/A.  There is some C-like psuedo-code; it is not compelete enough to
be compiled or checked, and is only used as an illustration.



  (1.k) The IESG approval announcement includes a Document
        Announcement Write-Up. Please provide such a Document
        Announcement Write-Up? Recent examples can be found in the
        "Action" announcements for approved documents. The approval
        announcement contains the following sections:

    Technical Summary
        Relevant content can frequently be found in the abstract
        and/or introduction of the document. If not, this may be
        an indication that there are deficiencies in the abstract
        or introduction.


From abstract:

This document discusses the use of the Internet Control Message
Protocol (ICMP) to perform a variety of attacks against the
Transmission Control Protocol (TCP) and other similar protocols.
Additionally, describes a number of widely implemented modifications
to TCP's handling of ICMP error messages that help to mitigate these
issues.


    Working Group Summary
        Was there anything in WG process that is worth noting? For
        example, was there controversy about particular points or
        were there decisions where the consensus was particularly
        rough?

None.


    Document Quality
        Are there existing implementations of the protocol? Have a
        significant number of vendors indicated their plan to
        implement the specification? Are there any reviewers that
        merit special mention as having done a thorough review,
        e.g., one that resulted in important changes or a
        conclusion that the document had no substantive issues? If
        there was a MIB Doctor, Media Type or other expert review,
        what was its course (briefly)? In the case of a Media Type
        review, on what date was the request posted?

There are several existing implementations that perform certain
activities described in this document.  These come from many
different vendors and other sources, and some are widely deployed.