Re: [tcpm] I-D Action: draft-ietf-tcpm-rfc793bis-08.txt
Gorry Fairhurst <gorry@erg.abdn.ac.uk> Thu, 05 April 2018 17:14 UTC
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To: Yuchung Cheng <ycheng@google.com>, "tcpm@ietf.org Extensions" <tcpm@ietf.org>
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From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
Organization: The University of Aberdeen is a charity registered in Scotland, No SC013683.
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Date: Thu, 05 Apr 2018 18:14:03 +0100
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Subject: Re: [tcpm] I-D Action: draft-ietf-tcpm-rfc793bis-08.txt
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A couple of comments-on-comments in-line, Gorry On 29/03/2018 15:10, Yuchung Cheng wrote: > Thanks for the update. I enjoy reading the new diffserv text. > > comments: > <quote> > The IPv4 specification [1] includes a precedence value in the Type of > precedence will still have to check the precedence of incoming Service > field (TOS), that was also modified in [15], and then > segments and possibly raise the precedence level they use on the > obsoleted by the definition of Differentiated Services (DiffServ) > connection. [6]. I think this text kind of suggests ToS still exists. DiffServ is mature technology. I think we shouldn't even be hinting that ToS semantics are permitted - I'd suggest we firmly state that Diffserv has obsoleted the former TOS semantics. > In DiffServ the former precedence values are treated as Class > Selector codepoints, and methods for compatible treatment are > described in the DiffServ architecture. The RFC 793/1122 TCP > specification includes logic intending to have connections use the > highest precedence requested by either endpoint application, and to > keep the precedence consistent throughout a connection. > Right, RFC 7657 has slightly more refined text in the same vein on not change DSCPs too often. > There is an > assumption of bidirectional/symmetric precedence values, however, the > DiffServ architecture is asymmetric. Problems were described in [17] > and the solution described is to ignore IP precedence in TCP. Since > RFC 2873 is a Standards Track document (although not marked as > updating RFC 793), these checks are no longer a part of the TCP > standard defined in this document, though the DiffServ field value is > still is a part of the interface between TCP and the network layer, /is still is/ > and values can be indicated both ways between TCP and the > application. > </quote> > > I am not entirely I get the main points this paragraph tries to convey. Are they > 1. a TCP stack MUST implement RFC2873 > 2. precedence is obsoleted. > ? > I think something does have to be said about the way diffserv works, although RFC 2873 is all the more vague by avoiding all keywords. > > <quote> > Note that the DiffServ field is permitted to change during a > connection (section 4.2.4.2 of RFC 1122). However, the > application interface might not support this ability, > Well always possible, but do we really need to say that, since it kind of breaks diffserv. > and the > application does not have knowledge about individual TCP > segments, so this can only be done on a coarse granularity, at > best. This limitation is further discussed in RFC 7657 (sec > 5.1, 5.3, and 6) [37]. Generally, an application SHOULD NOT > change the DiffServ field value during the course of a > connection. > </quote> > > The underlying assumptions of this text is > 1. Application can not specify precisely the DiffServ at TCP segments level > 2. TCP does not tolerate reordering well today > > As API and TCP evolve and socket API isn't the only one, it would be > good to be explicit about these assumptions. e.g. > "Generally an application SHOULD NOT change DiffServ field value > during the course of a connection because it may cause excessive > reorderings and adversely hurts performance" > > nits: > p32: s/the DiffServ field value is still is a part/ the DiffServ field > value still is a part / > p68: s/ SND.NEXT/SND.NXT/ > p47: s/TCP may be buffer the data/TCP may buffer the data/ > > On Wed, Mar 28, 2018 at 9:01 PM, <internet-drafts@ietf.org> wrote: >> >> A New Internet-Draft is available from the on-line Internet-Drafts directories. >> This draft is a work item of the TCP Maintenance and Minor Extensions WG of the IETF. >> >> Title : Transmission Control Protocol Specification >> Author : Wesley M. Eddy >> Filename : draft-ietf-tcpm-rfc793bis-08.txt >> Pages : 102 >> Date : 2018-03-28 >> >> Abstract: >> This document specifies the Internet's Transmission Control Protocol >> (TCP). TCP is an important transport layer protocol in the Internet >> stack, and has continuously evolved over decades of use and growth of >> the Internet. Over this time, a number of changes have been made to >> TCP as it was specified in RFC 793, though these have only been >> documented in a piecemeal fashion. This document collects and brings >> those changes together with the protocol specification from RFC 793. >> This document obsoletes RFC 793, as well as 879, 2873, 6093, 6429, >> 6528, and 6691 that updated parts of RFC 793. It updates RFC 1122, >> and should be considered as a replacement for the portions of that >> document dealing with TCP requirements. It updates RFC 5961 due to a >> small clarification in reset handling while in the SYN-RECEIVED >> state. >> >> RFC EDITOR NOTE: If approved for publication as an RFC, this should >> be marked additionally as "STD: 7" and replace RFC 793 in that role. >> >> >> >> The IETF datatracker status page for this draft is: >> https://datatracker.ietf.org/doc/draft-ietf-tcpm-rfc793bis/ >> >> There are also htmlized versions available at: >> https://tools.ietf.org/html/draft-ietf-tcpm-rfc793bis-08 >> https://datatracker.ietf.org/doc/html/draft-ietf-tcpm-rfc793bis-08 >> >> A diff from the previous version is available at: >> https://www.ietf.org/rfcdiff?url2=draft-ietf-tcpm-rfc793bis-08 >> >> >> Please note that it may take a couple of minutes from the time of submission >> until the htmlized version and diff are available at tools.ietf.org. >> >> Internet-Drafts are also available by anonymous FTP at: >> ftp://ftp.ietf.org/internet-drafts/ >> >> _______________________________________________ >> tcpm mailing list >> tcpm@ietf.org >> https://www.ietf.org/mailman/listinfo/tcpm > > _______________________________________________ > tcpm mailing list > tcpm@ietf.org > https://www.ietf.org/mailman/listinfo/tcpm >
- [tcpm] I-D Action: draft-ietf-tcpm-rfc793bis-08.t… internet-drafts
- Re: [tcpm] I-D Action: draft-ietf-tcpm-rfc793bis-… Yuchung Cheng
- Re: [tcpm] I-D Action: draft-ietf-tcpm-rfc793bis-… Gorry Fairhurst
- Re: [tcpm] I-D Action: draft-ietf-tcpm-rfc793bis-… Yuchung Cheng