Re: [pmtud] comments and discusses on draft-ietf-pmtud-method-10
Michael Tuexen <Michael.Tuexen@lurchi.franken.de> Thu, 26 October 2006 18:49 UTC
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From: Michael Tuexen <Michael.Tuexen@lurchi.franken.de>
Subject: Re: [pmtud] comments and discusses on draft-ietf-pmtud-method-10
Date: Thu, 26 Oct 2006 20:47:31 +0200
To: Lars Eggert <lars.eggert@netlab.nec.de>
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Dear all, just a comment regarding I-D.ietf-tsvwg-sctp-padding document. It was last called in the WG and the comments are integrated in the version currently available. Best regards Michael On Oct 26, 2006, at 6:31 PM, Lars Eggert wrote: > Hi, > > draft-ietf-pmtud-method-10 has gathered some discusses and comments > during IESG evaluation. The most serious one is probably David > Kessens'. I encourage the authors to try and resolve these with the > discussing ADs. > > Lars > > Jari Arkko: > Comment: > [2006-10-25] > Some protocols may require additional packets after > a loss to detect > > it promptly (e.g., TCP loss detection using duplicate > > acknowledgments). Such a protocol SHOULD wait until sufficient data > > and window space is available so that it will be able to transmit > > enough data after the probe to trigger the loss detection mechanism > > in the event of a lost probe. > > It would be useful to have some additional suggested > parameters that guide how long such wait should be. > > Brian Carpenter: > Discuss: > [2006-10-25] This is very welcome document and I hope this issue > can be quickly resolved: > > > 5.2. Storing PMTU information > ... > > If IPv6 flows are in use, an implementation MAY use the IPv6 > flow id > > [RFC2460][RFC1809] as the local representation of a path. > Packets > > sent to a particular destination but belonging to different > flows may > > use different paths, with the choice of path depending on the > flow > > id. This approach will result in the use of optimally sized > packets > > on a per-flow basis, providing finer granularity than MTU values > > maintained on a per-destination basis. > > One problem here is that the informative reference to RFC 1809 > needs to > be replaced by a normative reference to RFC 3697 (which updates 2460). > > The second problem is that the flow label is not a routing tag. > The second sentence is therefore very speculative. I believe the third > sentence is misleading and should say something much more tentative > such as "Such an approach could theoretically result...". > > Bill Fenner: > Comment: > [2006-10-25] Normative reference to draft-ietf-tsvwg-sctp-padding > may cause delay. > > Russ Housley: > Comment: > [2006-10-24] > COMMENT > > The Abstract seem a little bit long. Maybe it can be reworded to > include less of the information that is also in the Introduction. > > David Kessens: > Discuss: > [2006-10-26] > In section '7.2. Selecting initial values' > > It is RECOMMENDED that search_low be initially set to an MTU size > that is likely to work over a very wide range of environments. Given > today's technologies, a value of 512 bytes is probably safe. For > IPv6 flows, a value of 1280 bytes is appropriate. The initial value > for search_low SHOULD be configurable. > > When 1280 was selected as the minimum MTU for ipv6, it was choosen > because it was considered that there were no (reasonable) media that > cannot at least support a MTU of 1280 and that 1280 bytes was therefor > a 'safe value'. Why is it that this document > recommends a different value for ipv4 while it really deals with the > same problem. Basically, why penalize short lived tcp connections > over normal media for pathological cases ? > > Combined with the following advice in section '7.3. Selecting > probe size': > > However, for > some protocols, such as TCP, failed probes are more expensive than > successful ones, since data in a failed probe will need to be > retransmitted. For such protocols, a strategy that raises the probe > size in smaller increments might have lower overhead. > > it might take a long time before you reach the proper MTU size. > > Considering that I would not qualify 'TCP' as 'some' protocol as it > normally is the majority of all traffic on any network this can have > major consequences for the number of packets that need to be processed > by all routers in the network, especially with a large number of > short lived connections. In addition to this, the end-user > experience might > suffer as well. Obviously, this all depends on the exact algorithm > choosen > for raising the probe size which is underspecified at best. > > Did anybody do any research in this topic ? Did anybody run any > simulations based on the actual traffic mix that we see on the > Internet? > > Without that (please correct me if I am wrong), I believe we cannot > recommend this work as a Proposed Standard. Maybe experimental with > a clear warning that it supposed to be used to research the issue, but > not for full scale deployment. > > I also received a review by Pekka Savola from the Ops Directorate. > > Please fix the first issue that he brings up or convince me that he is > wrong ;-). See below for his full review: > > The first one is probably Discuss unless some other AD picks it up > first, the rest more editorial comments. > > Section 5.4: " It is worth noting that classical PMTUD does not > work at all as > +ICMP > PTB messages are never generated in response to packets with > multicast destination addresses [RFC1112][RFC2460]." > > ==> while this is correct for v4, it is not true for v6. RFC1981 > specifically includes text on how to do PMTUDv6 with multicast. > RFC2460 also includes discussion on how ICMP errors may be generated > in response to a multicast packet. See RFC 4443 section 2.4 clause > e.3. So, while this error must be corrected, it can easily be done by > just rewording (or removing) this paragraph and no further changes are > required. > > Abstract is not very abstract. A shorter, single paragraph version > might be better. > > Section 4: "All Internet nodes SHOULD implement PLPMTUD ..", yet the > doc says that each protocol needs to have its own implementation of > PLPMTUD. So it's not quite clear what the above requirement means. > That at least one of the protocols of the node should implement > PLPMTUD? > > Section 13.1, I-D.ietf-tsvwg-sctp-padding is a normative reference, > but the state is still "AD watching". Hence this document will have > to wait in the RFC-ed queue. > > Dan Romascanu: > Comment: > [2006-10-25] I like the way this document (especially section 7) > deals with operational and initial deployment considerations, > analyzing carefully the impact of the usage of the discovery method > in the Internet. > > Mark Townsley: > Comment: > [2006-10-25] > The abstract is very long. I recommend sticking with just the first > paragraph, and moving the rest to an introduction section > (eliminating redundant information). > > -- > Lars Eggert NEC Network > Laboratories > > > _______________________________________________ > pmtud mailing list > pmtud@ietf.org > https://www1.ietf.org/mailman/listinfo/pmtud _______________________________________________ pmtud mailing list pmtud@ietf.org https://www1.ietf.org/mailman/listinfo/pmtud
- [pmtud] comments and discusses on draft-ietf-pmtu… Lars Eggert
- Re: [pmtud] comments and discusses on draft-ietf-… Michael Tuexen
- [pmtud] Revised draft-ietf-pmtud-method-10 per IE… Matt Mathis
- [pmtud] Re: Revised draft-ietf-pmtud-method-10 pe… Brian E Carpenter
- Re: [pmtud] Revised draft-ietf-pmtud-method-10 pe… Lars Eggert