Hi Greg, FWIW, it might be useful to note that some L2s maintain ordering for their own purposes, e.g., ATM did so to simplify fragmentation and reassembly in its own protocol layers. Others may rely on in-order delivery for control messages (do Ethernet BPDUs require this?).
I.e., it’s not always something L2 does for IP… Joe — Dr. Joe Touch, temporal epistemologist www.strayalpha.com > On Mar 11, 2025, at 1:05 PM, Greg White > <g.white=40cablelabs....@dmarc.ietf.org> wrote: > > Hi all, > > There was a recent discussion on the QUIC and TSVWG mailing lists* regarding > the somewhat common implementation in L2 networks of guaranteeing in-order > delivery by delaying higher-sequenced L2 frames while waiting for a later > arriving lower-sequenced frame. This practice has been important > historically, but brings multiple costs due to implementation complexity and > L2 protocol complexity. In addition, the re-sequencing may end up doing more > harm than good, since it is generally done without knowledge of the > higher-layer protocol contexts (e.g. the late packet that triggers the delay > might be for a different TCP connection than the ones that get delayed). > Since modern TCPs and many QUIC implementations are tolerant of some > reordering, a few of us thought it would be worthwhile to have a broader > discussion and see if we could agree on new guidance that the IETF could > provide to L2 standards orgs. Intarea was suggested as being the most > appropriate WG to bring the discussion to. > > To that end, we've written a draft. The datatracker version (draft-00) is > linked below, but the version on GitHub is more up-to-date. > https://gwhitecl.github.io/draft-white-intarea-reordering/draft-white-intarea-reordering.html > > There is a short slot on the agenda on Monday to introduce the draft and get > reactions. > > Best regards, > Greg > > * > https://mailarchive.ietf.org/arch/browse/tsvwg/?gbt=1&q=%22Robustness%20to%20packet%20reordering%22 > > > > On 3/3/25, 3:56 PM, "internet-dra...@ietf.org > <mailto:internet-dra...@ietf.org>" <internet-dra...@ietf.org > <mailto:internet-dra...@ietf.org>> wrote: > > > A new version of Internet-Draft draft-white-intarea-reordering-00.txt has been > successfully submitted by Greg White and posted to the > IETF repository. > > > Name: draft-white-intarea-reordering > Revision: 00 > Title: Proposal for Updates to Guidance on Packet Reordering > Date: 2025-03-03 > Group: Individual Submission > Pages: 6 > URL: https://www.ietf.org/archive/id/draft-white-intarea-reordering-00.txt > <https://www.ietf.org/archive/id/draft-white-intarea-reordering-00.txt> > Status: https://datatracker.ietf.org/doc/draft-white-intarea-reordering/ > <https://datatracker.ietf.org/doc/draft-white-intarea-reordering/> > HTML: https://www.ietf.org/archive/id/draft-white-intarea-reordering-00.html > <https://www.ietf.org/archive/id/draft-white-intarea-reordering-00.html> > HTMLized: > https://datatracker.ietf.org/doc/html/draft-white-intarea-reordering > <https://datatracker.ietf.org/doc/html/draft-white-intarea-reordering> > > > > > Abstract: > > > Several link technology standards mandate that equipment guarantee > in-order delivery of layer 2 frames, apparently due to a belief that > this is required by higher layer protocols. In addition, certain > link types can introduce out-of-order arrivals at the end of the > layer 2 link, which the receiving equipment is required to rectify by > delaying higher sequenced frames until all lower sequenced frames can > be delivered or are deemed lost. The delaying of higher sequenced > frames is generally done without any knowledge of the higher layer > protocols in use, let alone any knowledge of higher layer protocol > contexts (e.g. TCP connections) in the case that the layer 2 link is > carrying a multiplex of such contexts. It could, for example, be the > case that all of the higher sequenced frames being delayed are > carrying packets for different layer 4 contexts than a single lower- > sequenced frame that triggered the delay. The result is that this > "re-sequencing" operation can introduce delays that result in > degradation of performance rather than improving it. Moreover, > modern, performant TCP and QUIC implementations support features that > significantly improve their tolerance to out-of-order delivery. > > > This draft is intended to promote an analysis and discussion of the > sensitivity of modern protocols to out-of-order delivery, and to > potentially develop new guidance to layer 2 technology standards > regarding the need to assure in-order delivery. > > > > > > > The IETF Secretariat > > > > > > > > _______________________________________________ > Int-area mailing list -- int-area@ietf.org > To unsubscribe send an email to int-area-le...@ietf.org
_______________________________________________ Int-area mailing list -- int-area@ietf.org To unsubscribe send an email to int-area-le...@ietf.org
