De : Warren Kumari [mailto:[email protected]] Envoyé : jeudi 3 août 2017 01:38 À : The IESG; SEITE Pierrick IMT/OLN Cc : Jouni Korhonen; [email protected]; [email protected]; [email protected] Objet : Re: RE : Warren Kumari's Discuss on draft-ietf-dmm-mag-multihoming-04: (with DISCUSS) On Wed, Aug 2, 2017 at 5:18 PM <[email protected]> wrote: Hello Please see inline Pierrick Sent from my cell phone, mind the typos. -------- Message d'origine -------- De : Warren Kumari <[email protected]> Date : 02/08/2017 22:23 (GMT+01:00) À : The IESG <[email protected]> Cc : [email protected], Jouni Korhonen <[email protected]>, [email protected], [email protected], [email protected] Objet : Warren Kumari's Discuss on draft-ietf-dmm-mag-multihoming-04: (with DISCUSS) Warren Kumari has entered the following ballot position for draft-ietf-dmm-mag-multihoming-04: Discuss When responding, please keep the subject line intact and reply to all email addresses included in the To and CC lines. (Feel free to cut this introductory paragraph, however.) Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html for more information about IESG DISCUSS and COMMENT positions. The document, along with other ballot positions, can be found here: https://datatracker.ietf.org/doc/draft-ietf-dmm-mag-multihoming/ ---------------------------------------------------------------------- DISCUSS: ---------------------------------------------------------------------- Section 3.2. Traffic distribution schemes "Per-packet management: the LMA and the MAG distribute packets, belonging to a same IP flow, over more than one bindings (i.e. more than one WAN interface)." This immediately made my out-of-order-packets antenna pop up, so I read the section looking for mitigations. The very next sentence reads: "Packet distribution can be done either at the transport level, e.g. using MPTCP or at When operating at the IP packet level, different packets distribution algorithms are possible. " -- the fact that this sentence is a: malformed and b: hand-wavy did nothing to allay my concerns, so I read further: "The distribution algorithm is left to implementer but whatever the algorithm is, packets distribution likely introduces packet latency and out-of-order delivery. LMA and MAG shall thus be able to make reordering before packets delivery." - I agree with the first sentence (although it is poorly worded), but the second sentence doesn't follow from the first; "shall thus be able to" implies that the prior text somehow provides a solution, not points out a problem (the sentence is also malformed)-- I think you mean something like "The LMA and MAG thus need to be able reorder packets to their original order before delivery." This then continues with "Sequence number can be can be used for that purpose, for example using GRE with sequence number option [RFC5845]." - I think that the actual reference should be RFC2890, but regardless of this, I don't think that what you are proposing works - "The Sequence Number field is used to maintain sequence of packets **within** the GRE Tunnel." (from RFC2890, emphasis added). This means that sequence numbers are local to the tunnel, and (as I understand it) your solution involves diverse tunnels. Further, Section 2.2. Sequence Number says: "The receiver may perform a small amount of buffering in an attempt to recover the original sequence of transmitted packets. In this case, the packet may be placed in a buffer sorted by sequence number." - if you are proposing using a single sequence number space for multiple tunnels, you will end up with sequence number space gabs, and lots of buffering, etc. The section ends with: "However, more detailed considerations on reordering and IP packet distribution scheme (e.g. definition of packets distribution algorithm) are out the scope of this document." - I think that, unless the prior paragraph is significantly reworked, it should not try and suggest any mitigations. >> ok The whole idea of striping packets of a flow across (notably) different transports seems like a really bad idea to me -- is it actually needed? >> some use-cases implement per-packet distribution. However this document does >> not aim to make recommendation on the way to distribute packets So, how do they deal with out of order packets? >> AFAIK, it is implementation specific and depends on the use-case: some >> implementation relies on MPTCP, some others have proprietary mechanisms >> adding sequence numbers to the tunneled packet. Sometimes, if only some >> specific application are supposed to take benefit of the aggregation, >> reordering is only managed at the application layer. W _________________________________________________________________________________________________________________________ Ce message et ses pieces jointes peuvent contenir des informations confidentielles ou privilegiees et ne doivent donc pas etre diffuses, exploites ou copies sans autorisation. Si vous avez recu ce message par erreur, veuillez le signaler a l'expediteur et le detruire ainsi que les pieces jointes. Les messages electroniques etant susceptibles d'alteration, Orange decline toute responsabilite si ce message a ete altere, deforme ou falsifie. Merci. This message and its attachments may contain confidential or privileged information that may be protected by law; they should not be distributed, used or copied without authorisation. If you have received this email in error, please notify the sender and delete this message and its attachments. As emails may be altered, Orange is not liable for messages that have been modified, changed or falsified. Thank you. -- I don't think the execution is relevant when it was obviously a bad idea in the first place. This is like putting rabid weasels in your pants, and later expressing regret at having chosen those particular rabid weasels and that pair of pants. ---maf
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