Re: [tcpm] Draft schepherd write-up for 793bis Thu, 10 June 2021 14:49 UTC

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To: "Scharf, Michael" <>, "" <>
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Thread-Topic: Draft schepherd write-up for 793bis
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Date: Thu, 10 Jun 2021 14:49:16 +0000
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Subject: Re: [tcpm] Draft schepherd write-up for 793bis
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Hi Michael, 

One comment about the IANA part, we have agreed to move one existing IANA **registry** to be a **sub-registry** under the existing TCP registry. I would update the IANA part accordingly. 

Other than that, this looks good. Thanks. 


> -----Message d'origine-----
> De : tcpm [] De la part de Scharf,
> Michael
> Envoyé : jeudi 10 juin 2021 11:03
> À :
> Cc : tcpm-chairs <>
> Objet : [tcpm] Draft schepherd write-up for 793bis
> Dear all,
> As document shepherd, I have started to work on my write-up for
> 793bis. Given that 793bis may one of the most important deliverables
> of TCPM, I'd like to ensure that the write-up correctly describes
> the TCPM consensus. Therefore, I share the text before actually
> hitting the button.
> If the write-up listed below is not accurate or misses important
> details, please let me know ASAP (on-list of off-list).
> I plan to forward 793bis to our AD tomorrow.
> Thanks
> Michael
> ***
> 1. Summary
> The document shepherd is Michael Scharf <michael.scharf@hs-
> The responsible Area Director is Martin Duke
> <>om>.
> This document specifies the Transmission Control Protocol (TCP) as
> "bis" document to RFC 793. It obsoletes RFC 793 as well as a several
> other RFCs that specified additions to RFC 793. It also updates RFC
> 1122, and it should be considered as a replacement for the portions
> of that document dealing with TCP requirements.
> The purpose of this document is to bring together all the IETF
> Standards Track changes that have been made to the base TCP
> functional specification and unify them into an update of RFC 793.
> The document focuses on the common basis all TCP implementations
> must support to interoperate. With one exception, protocol
> modifications compared to RFC 793 are limited to standards-track
> RFCs or verified erratas, i.e., changes of TCP standards that
> already have IETF consensus.
> RFC 793 and RFC 1122 are ubiquitously implemented Internet
> Standards. The same applies to 793bis. The TCPM working group
> requests publication of 793bis on Standards Track. If approved, the
> document should replace RFC 793 as "STD 7".
> 2. Review and Consensus
> The TCPM working group has worked on this document for more than 6
> years, and many TCPM contributors have reviewed the specification
> during that time. In particular, many TCP implementers have provided
> detailed comments based on operational experience. The document was
> relatively stable in the latest versions. During and after WGLC,
> several comprehensive reviews flagged some open issues that all got
> resolved.
> 793bis improves the specification of TCP but it does not modify the
> TCP protocol. TCP is a complex protocol and even minor wording
> details in the protocol specification can matter. Given the
> restriction to TCP changes that already have IETF consensus, there
> has never been any major controversy about the main content.
> Nonetheless, several questions were non-trivial and triggered longer
> discussions in TCPM. These issues can roughly be subdivided in three
> categories:
> 1/ Being published in 1981, RFC 793 defines several protocol
> mechanisms that have become outdated and may not be implemented at
> all in a modern TCP/IP stack. However, in some cases the
> corresponding specification in RFC 793 never got updated or
> obsoleted and is still formally valid. Appendix A.1 summarizes some
> of these issues. The TCPM consensus for those cases is to document
> the issues in 793bis, but not to change the TCP standards. The
> required changes to the TCP standards should be handled by
> dedicated, narrow-focused RFCs that would have to reach IETF
> consensus first. This de-risk strategy ensures that each TCP
> protocol change can be properly and comprehensively reviewed.
> 2/ There are some known issues in the standards-track specification
> of TCP that exist but only matter in corner cases. An example is
> documented in Appendix A.2. In Internet usage of TCP, these
> conditions are rarely occurring. Common operating systems include
> different alternative mitigations, and the standard has not been
> updated yet to codify one of them. Also, there is no known best
> approach. Given the lack of practical relevance, the TCPM consensus
> is to describe these known problems, but not to change the TCP
> standards in 793bis. Again, these problems could be solved by
> future, dedicated, narrow-focused RFC that would have to reach IETF
> consensus first.
> 3/ There are known deviations between mandatory-to-implement
> requirements in the TCP standard and some widely deployed
> implementations. An example are some details in Section 3.8.3, such
> as the numerical value in MUST-23. Those cases typically do not
> affect interoperability with other implementations. The TCPM working
> group has discussed whether to change the standard in such cases
> (e.g., downgrade MUST-23 to a SHOULD), but finally refrained from
> going down that road in 793bis, given the huge installed base with a
> very large variety of TCP implementations. Similar like in the
> previous cases, 793bis may get updated by narrow-focused RFCs.
> There is one important exception to the decision not to include new
> guidance in 793bis. The exception is Section 3.8.2 "TCP Congestion
> Control". TCP congestion control was developed after publication of
> RFC 793 and the state-of-the-art has evolved a lot as compared to
> RFC 1122. While there are numerous RFCs that specify TCP congestion
> control, there is no clear normative guidance on the required
> minimum in all TCP implementations that would be appropriate for
> 793bis. However, 793bis cannot just stay silent on congestion
> control. Given the lack of other applicable wording in existing
> standards, Section 3.8.2 includes new text and is therefore
> different to the rest of the document. Section 3.8.2 was
> comprehensively reviewed by the TCPM working group and in particular
> by TCP implementers. The section is short and straightforward, and
> the wording was chosen very carefully to reflect existing TCP
> standards and operational experience in the Internet. Also, given
> ongoing research, TCP conge  stion control will most likely further
> evolve in future. Section 3.8.2 enables such a further evolution
> while defining important base requirements.
> Running code exists - in billions of TCP/IP stacks. Given the very
> limited scope of modifications in the 793bis document, all TCP
> implementations that are already compliant to the TCP standards
> before publication of 793bis should be compliant to 793bis as well.
> The shepherd believes that the 793bis document has unanimous support
> from the entire TCPM working group.
> 3. Intellectual Property
> The editor has stated that his direct, personal knowledge of any IPR
> related to this document has already been disclosed, in conformance
> with BCPs 78 and 79. The editor is not aware of any IPR relevant for
> the base TCP protocol. Since 793bis does not change the TCP
> protocol, relevant IPR would have to be disclosed already for the
> existing RFCs included in 793bis.
> There is a Cisco IPR disclosure from year 2004 related to the
> Internet-Draft that resulted in RFC 5961
> ( RFC 5961 is one source of
> changes included in 793bis. In all places in 793bis where the
> recommendations from RFC 5961 are mentioned, 5961 is prominently
> referenced. RFC 5961 mostly affects MAY-12 in 793bis, i.e., the
> changes described in RFC 5961 are optional and not mandatory-to-
> implement.
> It has been suggested that the owner of the IPR disclosed in
> updates the IPR disclosure to
> make clear whether it applies to 793bis, or not.
> The TCPM working group is aware of the IPR disclosure related to RFC
> 5961, which is known already for a long time. The document shepherd
> has verified on the TCPM mailing list that the TCPM working group is
> fine with the proposed text in 793bis related to RFC 5961. In the
> TCPM working group there are no known concerns regarding this IPR
> disclosure related to an optional mechanism.
> 4. Other Points
> The intended status listed in the document is "Proposed Standard".
> As all main TCP implementations are supposed to comply with 793bis,
> the document may fulfill the requirements of an "Internet Standard"
> according to RFC 2026 and RFC 7127.
> idnits reports some warnings, such as obsolete references. These are
> all false positives. The document refers to some obsolete documents
> to provide historical context.
> The IANA Considerations in Section 5 include some editorial clean-up
> of the TCP entries in the IANA registry. The modifications neither
> change any allocation nor any policy in the IANA registry. These
> purely editorial changes have been discussed in the TCPM working
> group for a long time and there is unanimous consensus in TCPM that
> this clean-up is useful.
> All errata to RFC 793 and related RFCs have been considered in this
> "bis" document.
> When Wes started working on a 793bis document in 2013, the document
> shepherd, as well as many other TCPM contributors, were pretty
> convinced that writing a 793bis document is an impossible endeavor.
> Well, after many years, we are proven wrong. Many thanks to Wes as
> editor!
> _______________________________________________
> tcpm mailing list


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