Re: Never fragment: getting PMTU info transmitted reliably
Michael Richardson <mcr+ietf@sandelman.ca> Thu, 17 January 2019 02:39 UTC
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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Brian E Carpenter <brian.e.carpenter@gmail.com>
cc: "Joel M. Halpern" <jmh@joelhalpern.com>, IPv6 List <ipv6@ietf.org>
Subject: Re: Never fragment: getting PMTU info transmitted reliably
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Date: Wed, 16 Jan 2019 21:39:41 -0500
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Brian E Carpenter <brian.e.carpenter@gmail.com> wrote: > On 2019-01-17 13:12, Joel M. Halpern wrote: >> Just to clarify one aspect of the way entropy in path selection, I want >> to point out a complication. >> >> It is not anywhere near enough to have as much entropy data as the >> number of choices. The problem is that you need enough randomness so >> that you can expect a good distribution of flows. And that even the >> smaller number of larger flows will likely get distributed across the >> choices. Reducing the amount of available entropy can be quite >> problematic. > Right. And for the server farm case, I don't think it's science fiction > these days to think about hundreds or thousands of servers. Also, if the > load sharing algorithm attempts to ensure that a given server has only > one big job at a time, then a high collision rate in the hash can > defeat it. A form of the birthday paradox applies: not "what is the > chance of a clash per flow" but "what is the chance that out of a > thousand servers, one of them gets two big jobs at the same time"? Based upon my reading of the netflix blogs, they have experiemented extensively with the load sharing, and they really don't care about flow-labels in their decision process. (Of course, because IPv4 has no such things) It's about how fresh the (disk read) caches on the servers are, what content is being streamed, and other things that have nothing to do with the packets themselves. Architecturally with IPv6, if you have an entire /64 (or more) to play with and you can statelessly forward packets at wire speed, then there are other interesting off-path choices one can do. (For instance, assign new server/128 for each client connection, and then when the connection arrives, dynamically map it to a particular server. This pushes the state storage from layer-4 to the neighbour cache, which might not be a win) So I seriously question whether any of this matters to server farms. > I am strongly against breaking the flow label just at the time when > the major o/s are starting to set it correctly. :-) > I'm all for fixing the fragmentation problem; > draft-ietf-intarea-frag-fragile > exists for a reason. But not by breaking something else. My quick read says that it looks great to me. Again, I don't really think that using the flow label to seed PLPMTUD is much of a win, but if it did provide something useful, I think it could be done without too much harm. To reiterate: I don't think the benefit is high enough to warrant the risk, despite the fact that I don't think the risk is as high as you are suggesting. -- ] Never tell me the odds! | ipv6 mesh networks [ ] Michael Richardson, Sandelman Software Works | IoT architect [ ] mcr@sandelman.ca http://www.sandelman.ca/ | ruby on rails [ -- Michael Richardson <mcr+IETF@sandelman.ca>, Sandelman Software Works -= IPv6 IoT consulting =-
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- Re: Non-Last Small IPv6 Fragments Bob Hinden
- Re: Non-Last Small IPv6 Fragments 神明達哉
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- RE: Non-Last Small IPv6 Fragments Ron Bonica
- Re: Non-Last Small IPv6 Fragments Erik Kline
- RE: Non-Last Small IPv6 Fragments Ron Bonica
- Re: Non-Last Small IPv6 Fragments Brian E Carpenter
- RE: Non-Last Small IPv6 Fragments Ron Bonica
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Mark Andrews
- Re: Non-Last Small IPv6 Fragments Simon Hobson
- Re: Non-Last Small IPv6 Fragments Erik Kline
- Re: Non-Last Small IPv6 Fragments David Farmer
- Re: Non-Last Small IPv6 Fragments Mark Andrews
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Erik Kline
- Re: Non-Last Small IPv6 Fragments Carsten Bormann
- Re: Non-Last Small IPv6 Fragments 神明達哉
- Re: Non-Last Small IPv6 Fragments Brian E Carpenter
- Re: Non-Last Small IPv6 Fragments Brian E Carpenter
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Mikael Abrahamsson
- Re: Non-Last Small IPv6 Fragments Mark Andrews
- Re: Non-Last Small IPv6 Fragments Bjoern A. Zeeb
- Re: Non-Last Small IPv6 Fragments Bjoern A. Zeeb
- Re: Non-Last Small IPv6 Fragments Timothy Winters
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Ole Troan
- Re: Non-Last Small IPv6 Fragments Timothy Winters
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Simon Hobson
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments David Farmer
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- RE: Non-Last Small IPv6 Fragments Ron Bonica
- Re: Non-Last Small IPv6 Fragments David Farmer
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Bob Hinden
- Re: Non-Last Small IPv6 Fragments David Farmer
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Erik Kline
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Christian Huitema
- Re: Non-Last Small IPv6 Fragments Ole Troan
- RE: Non-Last Small IPv6 Fragments Lubashev, Igor
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Ole Troan
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Ole Troan
- Re: Non-Last Small IPv6 Fragments Nick Hilliard
- Re: Non-Last Small IPv6 Fragments Bob Hinden
- Re: Non-Last Small IPv6 Fragments Brian E Carpenter
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Ole Troan
- Re: Non-Last Small IPv6 Fragments Nick Hilliard
- Re: Non-Last Small IPv6 Fragments Ole Troan
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Nick Hilliard
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Brian E Carpenter
- RE: Non-Last Small IPv6 Fragments Manfredi (US), Albert E
- Re: Non-Last Small IPv6 Fragments Bjoern A. Zeeb
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Brian E Carpenter
- Re: Non-Last Small IPv6 Fragments Erik Kline
- Re: Non-Last Small IPv6 Fragments Mark Smith
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Simon Hobson
- Re: Non-Last Small IPv6 Fragments Nick Hilliard
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Nick Hilliard
- Re: Non-Last Small IPv6 Fragments Bjoern A. Zeeb
- Re: Non-Last Small IPv6 Fragments Simon Hobson
- Re: Non-Last Small IPv6 Fragments Nick Hilliard
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- Re: Non-Last Small IPv6 Fragments Brian E Carpenter
- Re: Non-Last Small IPv6 Fragments Mark Andrews
- Re: Non-Last Small IPv6 Fragments Erik Kline
- Re: Non-Last Small IPv6 Fragments Nick Hilliard
- Re: Non-Last Small IPv6 Fragments Ole Troan
- Re: Non-Last Small IPv6 Fragments Erik Kline
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Tom Herbert
- End-to-end (was Re: Non-Last Small IPv6 Fragments) Christian Huitema
- Re: End-to-end (was Re: Non-Last Small IPv6 Fragm… Tom Herbert
- Re: End-to-end (was Re: Non-Last Small IPv6 Fragm… Nick Hilliard
- Re: Non-Last Small IPv6 Fragments Warren Kumari
- Re: Non-Last Small IPv6 Fragments Brian E Carpenter
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: End-to-end (was Re: Non-Last Small IPv6 Fragm… Fernando Gont
- Re: Non-Last Small IPv6 Fragments Mikael Abrahamsson
- Re: Non-Last Small IPv6 Fragments Tim Chown
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Warren Kumari
- Re: End-to-end (was Re: Non-Last Small IPv6 Fragm… Tom Herbert
- Re: Non-Last Small IPv6 Fragments Ole Troan
- Re: End-to-end (was Re: Non-Last Small IPv6 Fragm… Fernando Gont
- Re: Non-Last Small IPv6 Fragments Fernando Gont
- Re: Non-Last Small IPv6 Fragments Fred Baker
- Re: Non-Last Small IPv6 Fragments Tim Chown
- Re: End-to-end (was Re: Non-Last Small IPv6 Fragm… Tom Herbert
- Re: End-to-end (was Re: Non-Last Small IPv6 Fragm… Brian E Carpenter
- Re: Non-Last Small IPv6 Fragments Brian E Carpenter
- Re: Non-Last Small IPv6 Fragments Michael Richardson
- Never fragment: getting PMTU info transmitted rel… Michael Richardson
- Re: Never fragment: getting PMTU info transmitted… Joel M. Halpern
- Re: Never fragment: getting PMTU info transmitted… Brian E Carpenter
- Re: Never fragment: getting PMTU info transmitted… Tom Herbert
- Re: Never fragment: getting PMTU info transmitted… Michael Richardson
- Re: Never fragment: getting PMTU info transmitted… Brian E Carpenter
- Re: Never fragment: getting PMTU info transmitted… Mark Smith
- Re: Never fragment: getting PMTU info transmitted… Erik Kline
- Re: Never fragment: getting PMTU info transmitted… Mark Smith
- Re: Never fragment: getting PMTU info transmitted… Tom Herbert
- Re: Never fragment: getting PMTU info transmitted… Brian E Carpenter
- RE: Never fragment: getting PMTU info transmitted… Lubashev, Igor
- Re: Never fragment: getting PMTU info transmitted… Tom Herbert
- RE: Never fragment: getting PMTU info transmitted… Lubashev, Igor
- Re: Never fragment: getting PMTU info transmitted… C. M. Heard
- Re: Never fragment: getting PMTU info transmitted… Christian Huitema