Network Time Protocol Version 4: Port Randomization
draft-ietf-ntp-port-randomization-08

[Ballot comment]
Thank you to Sean Turner for the SECDIR review.

** Section 3.5.  Editorial. No issues with the text here.  However, it seems to duplicate what was already said in Section 3.1.

** Section 7.  Consider adding informal references for CVE-2019-11331 (https://nvd.nist.gov/vuln/detail/CVE-2019-11331)

[Ballot comment]
Thanks for this document. Thanks to all the reviewers, specially Brian Trammell for his TSVART review.

I have two observations,

    *  it says "This issue has been tracked by US-CERT with VU#597821, and has been
  assigned CVE-2019-11331." Please provide proper reference to the mentioned terminologies and assignment.

    *  removal of section 5: I don't think implementation status is a bad idea to be included in the memo. If not in a section, may be as appendix.

[Ballot comment]
Hi,

Thanks for this document.

Like Ben's comment, I was wondering why the document doesn't give a stronger recommendation as to which of the two approaches to follow.  It looks like all the implementations that the document lists already take the per-association approach, and that approach seems to be sufficient.  Hence, would it not be simpler to make that the RECOMMENDED approach, and then say that implementations MAY do per request randomization, but need to be aware that individual requests are more likely to take different paths with different latencies?

Thanks,
Rob

[Ballot comment]
There's a few places where we say things like "the choice of whether to
randomize the ephemeral port number on a per-request or a
per-association basis is left to the implementation, and should consider
the possible effects on path selection along with its possible impact on
time measurement."  But the main specific consideration that we mention
is that in ECMP and similar situations, randomizing per-request can
cause problems; in particular, I don't remember seeing anything that
would be an argument in favor of randomizing on a per-request basis.  So
the current guidance (entirely up to the implementation) doesn't seem to
match up very well with what we say about the two choices.  I think I'm
missing (in the text, that is) some aspect about how randomizing the
port on a per-request basis provides more robust defence against
off-path attacks than only randomizing per-association.

Section 3.3

  inspecting the source and destination port numbers.  Implementation
  of port randomization for non-symmetrical modes allows for simple
  differentiation of NTP requests and responses, and for the
  enforcement of security policies that may be valuable for the
  mitigation of DDoS attacks, when all NTP clients in a given network
  employ port randomization.

I guess the details of what those security policies might look like are
properly out of scope for this document ... but the potential
consequences of such policies on clients that don't employ port
randomization might be in scope for us.

Section 4

Just an observation (no need to change anything), but we seem to be
going from three lines of content in the original to 30 lines of content
in the new version.  If it was actually applied and viewed in context in
the manner of inline errata, the new text might feel a bit out of place.


NITS

Abstract

  number.  However, in the case of NTP modes where the use of a well-
  known port is not required, employing such well-known port
  unnecessarily increases the ability of attackers to perform blind/
  off-path attacks.  This document formally updates RFC5905,

"increases" has some implicit baseline, which is typically "the current
state prior to this document" (which is not the right baseline for this
case).  I'd suggest just "unnecessarily enables blind/off-path attacks",
or maybe a variant with "facilitates" rather than "enables".
(Similarly for the Introduction, twice.)

Section 7

  known for a long time now.  However, the NTP specification has
  traditionally followed a pattern of employing common settings and
  code even when not strictly necessary, which at times has resulted in
  negative security and privacy implications (see e.g.

It seems unusual for the NTP *specification* to employ common *code*.

  This issue has been tracked by US-CERT with VU#597821, and has been
  assigned CVE-2019-11331.

I failed to find anything under us-cert.gov that referenced "VU#597821"
or even just "597821".

[Ballot comment]
Thank you for the work on this document, short and to the point.

I only have one nit comment and a non-blocking comment.

Francesca

1. -----

  some off-path attacks (see e.g.  [NTP-FRAG].  This document aligns

FP: missing ")"

2. -----

  This issue has been tracked by US-CERT with VU#597821, and has been
  assigned CVE-2019-11331.

FP: I am just not sure that this sentence adds anything without some reference...

[Ballot comment]
Thank you for the work put into this document.

Please find below some non-blocking COMMENT points (but replies would be appreciated), and some nits.

Thanks to Karen O'Donoghue for her shepherd's write-up.

I hope that this helps to improve the document,

Regards,

-éric

== COMMENTS ==

-- Section 3.4 --
A reference for "Some NAT devices" would be welcome even if this behavior is to be expected.

The last § is convoluted and requires several read to understand it, paraphrasing would be good even if I have no suggestion.

-- Section 4 --
I wonder the added value of "The value in this variable becomes the source port number of packets sent from this association." Especially as 'variable' is not bound in the text to any value (OK we can guess that it is dstport).

Some rationale for "The randomized port number SHOULD NOT be shared with other associations." would be welcome. Also, is it OK to share this port number with other applications ?

-- Section 5 --
Interesting to read that many existing implementations have always implemented this specification

     
== NITS ==

Please address all nits detected by:
https://www6.ietf.org/tools/idnits?url=https://www.ietf.org/archive/id/draft-ietf-ntp-port-randomization-06.txt

-- Section 8 --
Unusual last paragraph in the acknowledgements ;-)

[Ballot comment]
All comments below are about very minor potential issues that you may choose to
address in some way - or ignore - as you see fit. Some were flagged by
automated tools (via https://github.com/larseggert/ietf-reviewtool), so there
will likely be some false positives. There is no need to let me know what you
did with these suggestions.

Document references draft-irtf-pearg-numeric-ids-generation-03, but -07 is the
latest available revision.

These URLs in the document can probably be converted to HTTPS:
* http://leapsecond.com/ntp/NTP_Paper_Sommars_PTTI2017.pdf
* http://www.cs.bu.edu/~goldbe/papers/NTPattack.pdf

(Via drafts-lastcall@iana.org): IESG/Authors/WG Chairs:

The IANA Functions Operator has reviewed draft-ietf-ntp-port-randomization-06, which is currently in Last Call, and has the following comments:

We understand that this document doesn't require any registry actions.

While it's often helpful for a document's IANA Considerations section to remain in place upon publication even if there are no actions, if the authors strongly prefer to remove it, we do not object.

If this assessment is not accurate, please respond as soon as possible.

Thank you,

Sabrina Tanamal
Senior IANA Services Specialist

The following Last Call announcement was sent out (ends 2021-02-25):

From: The IESG
To: IETF-Announce
CC: draft-ietf-ntp-port-randomization@ietf.org, ek.ietf@gmail.com, ntp-chairs@ietf.org, ntp@ietf.org, odonoghue@isoc.org
Reply-To: last-call@ietf.org
Sender:
Subject: Last Call:  (Port Randomization in the Network Time Protocol Version 4) to Proposed Standard


The IESG has received a request from the Network Time Protocol WG (ntp) to
consider the following document: - 'Port Randomization in the Network Time
Protocol Version 4'
  as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits final
comments on this action. Please send substantive comments to the
last-call@ietf.org mailing lists by 2021-02-25. Exceptionally, comments may
be sent to iesg@ietf.org instead. In either case, please retain the beginning
of the Subject line to allow automated sorting.

Abstract


  The Network Time Protocol can operate in several modes.  Some of
  these modes are based on the receipt of unsolicited packets, and
  therefore require the use of a well-known port as the local port
  number.  However, in the case of NTP modes where the use of a well-
  known port is not required, employing such well-known port
  unnecessarily increases the ability of attackers to perform blind/
  off-path attacks.  This document formally updates RFC5905,
  recommending the use of transport-protocol ephemeral port
  randomization for those modes where use of the NTP well-known port is
  not required.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-ntp-port-randomization/



No IPR declarations have been submitted directly on this I-D.

(1) What type of RFC is being requested (BCP, Proposed Standard, Internet Standard, Informational, Experimental, or Historic)? Why is this the proper type of RFC? Is this type of RFC indicated in the title page header?

Proposed standard. The RFC type is indicated on the title page header.

This document updates RFC5905, replacing text from RFC5095 to recommend the use of transport-protocol ephemeral port randomization for NTP modes where use of the service port is not required. Thus, it requires a Standards Track document.


(2) 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.

The Network Time Protocol can operate in several modes.  Some of these modes are based on the receipt of unsolicited packets, and therefore require the use of a well-known port as the local port number.  However, in the case of NTP modes where the use of a well-known port is not required, employing such well-known port unnecessarily increases the ability of attackers to perform blind/off-path attacks.  This document formally updates RFC5905, recommending the use of transport-protocol ephemeral port randomization for those modes where use of the NTP well-known port is not required.
 
 
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?

There was nothing particularly noteworthy in the WG process.


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, YANG 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 multiple implementations of the document. They are discussed in Section 5, entitled "Implementation Status".


Personnel:

Who is the Document Shepherd? Who is the Responsible Area Director?

Karen O'Donoghue is the Document Shepherd. Erik Kline is the Responsible Area Director.


(3) Briefly describe the review of this document that was performed by the Document Shepherd. If this version of the document is not ready for publication, please explain why the document is being forwarded to the IESG.

This document is an update of RFC5905. The document shepherd has reviewed the proposed change to that document, and has performed a thorough read of the entire document.


(4) Does the document Shepherd have any concerns about the depth or breadth of the reviews that have been performed?

No.


(5) Do portions of the document need review from a particular or from broader perspective, e.g., security, operational complexity, AAA, DNS, DHCP, XML, or internationalization? If so, describe the review that took place.

No.


(6) Describe any specific concerns or issues that the Document Shepherd has 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.

There are no concerns.


(7) Has each author confirmed that any and all appropriate IPR disclosures required for full conformance with the provisions of BCP 78 and BCP 79 have already been filed. If not, explain why?

All co-authors have confirmed conformance.


(8) Has an IPR disclosure been filed that references this document? If so, summarize any WG discussion and conclusion regarding the IPR disclosures.

No.


(9) 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 is WG consensus behind the document.


(10) 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 publicly available.)

No.


(11) Identify any ID nits the Document Shepherd has found in this document. (See http://www.ietf.org/tools/idnits/ and the Internet-Drafts Checklist). Boilerplate checks are not enough; this check needs to be thorough.

ID nits was run on 11 Feb 2021. The results at that time were:
Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--).
These are minor issues that will be addressed during the next stage of publication including the update of an outdated informative reference.

(12) Describe how the document meets any required formal review criteria, such as the MIB Doctor, YANG Doctor, media type, and URI type reviews.

None required.


(13) Have all references within this document been identified as either normative or informative?

Yes.


(14) 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 plan for their completion?

No.


(15) Are there downward normative references references (see RFC 3967)? If so, list these downward references to support the Area Director in the Last Call procedure.

There are no downward references.


(16) Will publication of this document change the status of any existing RFCs? Are those RFCs listed on the title page header, listed in the abstract, and discussed in the introduction? If the RFCs are not listed in the Abstract and Introduction, explain why, and point to the part of the document where the relationship of this document to the other RFCs is discussed. If this information is not in the document, explain why the WG considers it unnecessary.

This document updates RFC5905. This is listed on the title page header and the abstract, and discussed in the introduction.


(17) Describe the Document Shepherd's review of the IANA considerations section, especially with regard to its consistency with the body of the document. Confirm that all protocol extensions that the document makes are associated with the appropriate reservations in IANA registries. Confirm that any referenced IANA registries have been clearly identified. Confirm that newly created IANA registries include a detailed specification of the initial contents for the registry, that allocations procedures for future registrations are defined, and a reasonable name for the new registry has been suggested (see RFC 8126).

There are no IANA considerations.


(18) List any new IANA registries that require Expert Review for future allocations. Provide any public guidance that the IESG would find useful in selecting the IANA Experts for these new registries.

None.


(19) Describe reviews and automated checks performed by the Document Shepherd to validate sections of the document written in a formal language, such as XML code, BNF rules, MIB definitions, YANG modules, etc.

None.


(20) If the document contains a YANG module, has the module been checked with any of the recommended validation tools (https://trac.ietf.org/trac/ops/wiki/yang-review-tools) for syntax and formatting validation? If there are any resulting errors or warnings, what is the justification for not fixing them at this time? Does the YANG module comply with the Network Management Datastore Architecture (NMDA) as specified in RFC8342?

This document does not contain a YANG module.

(1) What type of RFC is being requested (BCP, Proposed Standard, Internet Standard, Informational, Experimental, or Historic)? Why is this the proper type of RFC? Is this type of RFC indicated in the title page header?

Proposed standard. The RFC type is indicated on the title page header.

This document updates RFC5905, replacing text from RFC5095 to recommend the use of transport-protocol ephemeral port randomization for NTP modes where use of the service port is not required. Thus, it requires a Standards Track document.


(2) 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.

The Network Time Protocol can operate in several modes.  Some of these modes are based on the receipt of unsolicited packets, and therefore require the use of a well-known port as the local port number.  However, in the case of NTP modes where the use of a well-known port is not required, employing such well-known port unnecessarily increases the ability of attackers to perform blind/off-path attacks.  This document formally updates RFC5905, recommending the use of transport-protocol ephemeral port randomization for those modes where use of the NTP well-known port is not required.
 
 
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?

There was nothing particularly noteworthy in the WG process.


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, YANG 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 multiple implementations of the document. They are discussed in Section 5, entitled "Implementation Status".


Personnel:

Who is the Document Shepherd? Who is the Responsible Area Director?

Karen O'Donoghue is the Document Shepherd. Erik Kline is the Responsible Area Director.


(3) Briefly describe the review of this document that was performed by the Document Shepherd. If this version of the document is not ready for publication, please explain why the document is being forwarded to the IESG.

This document is an update of RFC5905. The document shepherd has reviewed the proposed change to that document, and has performed a thorough read of the entire document.


(4) Does the document Shepherd have any concerns about the depth or breadth of the reviews that have been performed?

No.


(5) Do portions of the document need review from a particular or from broader perspective, e.g., security, operational complexity, AAA, DNS, DHCP, XML, or internationalization? If so, describe the review that took place.

No.


(6) Describe any specific concerns or issues that the Document Shepherd has 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.

There are no concerns.


(7) Has each author confirmed that any and all appropriate IPR disclosures required for full conformance with the provisions of BCP 78 and BCP 79 have already been filed. If not, explain why?

All co-authors have confirmed conformance.


(8) Has an IPR disclosure been filed that references this document? If so, summarize any WG discussion and conclusion regarding the IPR disclosures.

No.


(9) 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 is WG consensus behind the document.


(10) 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 publicly available.)

No.


(11) Identify any ID nits the Document Shepherd has found in this document. (See http://www.ietf.org/tools/idnits/ and the Internet-Drafts Checklist). Boilerplate checks are not enough; this check needs to be thorough.

ID nits was run on 11 Feb 2021. The results at that time were:
Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--).
These are minor issues that will be addressed during the next stage of publication including the update of an outdated informative reference.

(12) Describe how the document meets any required formal review criteria, such as the MIB Doctor, YANG Doctor, media type, and URI type reviews.

None required.


(13) Have all references within this document been identified as either normative or informative?

Yes.


(14) 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 plan for their completion?

No.


(15) Are there downward normative references references (see RFC 3967)? If so, list these downward references to support the Area Director in the Last Call procedure.

There are no downward references.


(16) Will publication of this document change the status of any existing RFCs? Are those RFCs listed on the title page header, listed in the abstract, and discussed in the introduction? If the RFCs are not listed in the Abstract and Introduction, explain why, and point to the part of the document where the relationship of this document to the other RFCs is discussed. If this information is not in the document, explain why the WG considers it unnecessary.

This document updates RFC5905. This is listed on the title page header and the abstract, and discussed in the introduction.


(17) Describe the Document Shepherd's review of the IANA considerations section, especially with regard to its consistency with the body of the document. Confirm that all protocol extensions that the document makes are associated with the appropriate reservations in IANA registries. Confirm that any referenced IANA registries have been clearly identified. Confirm that newly created IANA registries include a detailed specification of the initial contents for the registry, that allocations procedures for future registrations are defined, and a reasonable name for the new registry has been suggested (see RFC 8126).

There are no IANA considerations.


(18) List any new IANA registries that require Expert Review for future allocations. Provide any public guidance that the IESG would find useful in selecting the IANA Experts for these new registries.

None.


(19) Describe reviews and automated checks performed by the Document Shepherd to validate sections of the document written in a formal language, such as XML code, BNF rules, MIB definitions, YANG modules, etc.

None.


(20) If the document contains a YANG module, has the module been checked with any of the recommended validation tools (https://trac.ietf.org/trac/ops/wiki/yang-review-tools) for syntax and formatting validation? If there are any resulting errors or warnings, what is the justification for not fixing them at this time? Does the YANG module comply with the Network Management Datastore Architecture (NMDA) as specified in RFC8342?

This document does not contain a YANG module.