Necroing and piggybacking on this old thread to expand on my at-the-mic-comment about concerns around IP fragmentation.
My concern is that with IPv4aaS technologies such as 464XLAT, MAP and lw4over6, we have pushed NAT64 translation/encapsulation down to the mobile UE and fixed-line CEs; fragmented packets--which are sometimes unavoidable with the additional encapsulation in or translation to IPv6--require reassembling, and depending on the implementation that will at best consume more resources and at worst be consistently dropped if the hashing is consistent across retransmits. I realise the argument about it consuming more resources and effort on the CE Router or UE is just me saying that I'd rather keep that problem upstream, so I'm more concerned about the risk where fragments are consistently dropped having a permanent impact on packet delivery. -Rich On Thu, 13 Mar 2025 at 00:31, [email protected] <[email protected]> wrote: > Fragment reassembly is one reason. Another non-transport reason is IPsec > replay. But in both cases, it’s not just ordering that matters; it varies > depending on whether the stream is reordered in isolation or different > reordered streams are concurrent. > > - in all cases, reordering matters within in a ’stream’, but the > definition of ’stream’ varies > IPsec = IP addresses + SPI > IP reassembly = IP addresses + FragID > > - out of order impact differs > IPsec = > reordering within a stream causes later packets of the same stream to the > dropped as replay attacks > interleaving of different reordered streams has no new impact over > interleaving of order-preserving streams > IPreassembly = > reordering within a stream set may or may not have any impact over > interleaving of order preserving streams > interleaving of different reordered streams consumes more resources, as > each pending stream requires a max-receive buffer > Otherwise, I can’t see a good reason either. > > Joe > > — > Dr. Joe Touch, temporal epistemologist > www.strayalpha.com > > On Mar 12, 2025, at 5:10 PM, Joel Halpern <[email protected]> wrote: > > I am trying to think why IP (as distinct from TCP / QUIC / ..) would care > about ordering at all. I suppose the corner case of reordered fragments > could be considered relevant to IP. But mostly, this seems to belong at > transport, not IP. > > Yours, > > Joel > > PS: I think the wording in the draft could be clearer that this is data > for input to L2 standards bodies, not recommendations for behavior at L2. > On 3/12/2025 8:02 PM, Greg White wrote: > > Thanks Joe. > > Yes, that could be case, but IMO it would be out of scope for the draft to > explore non-IP use cases. > > Perhaps the goal of this document could be described as gathering the > current wisdom around the implications, positive and negative, of L2 > resequencing on IP. > > Greg > > On Mar 12, 2025, at 5:32 PM, [email protected] wrote: > > 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 > <[email protected]> > <[email protected]> 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, "[email protected] > <mailto:[email protected]> <[email protected]>" < > [email protected] <mailto:[email protected]> > <[email protected]>> 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> > <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/> > <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> > <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> > <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 -- [email protected] > To unsubscribe send an email to [email protected] > > > > _______________________________________________ > Int-area mailing list -- [email protected] > To unsubscribe send an email to [email protected] > > > _______________________________________________ > Int-area mailing list -- [email protected] > To unsubscribe send an email to [email protected] >
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