Re: [tsvwg] Robert Wilton's No Objection on draft-ietf-tsvwg-datagram-plpmtud-19: (with COMMENT)

Jonathan Morton <chromatix99@gmail.com> Fri, 10 April 2020 14:02 UTC

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From: Jonathan Morton <chromatix99@gmail.com>
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Date: Fri, 10 Apr 2020 17:02:00 +0300
Cc: "Rodney W. Grimes" <ietf@gndrsh.dnsmgr.net>, Gorry Fairhurst <gorry@erg.abdn.ac.uk>, "tsvwg@ietf.org" <tsvwg@ietf.org>, Robert Wilton <rwilton@cisco.com>, "draft-ietf-tsvwg-datagram-plpmtud@ietf.org" <draft-ietf-tsvwg-datagram-plpmtud@ietf.org>, "tsvwg-chairs@ietf.org" <tsvwg-chairs@ietf.org>, The IESG <iesg@ietf.org>
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To: Spencer Dawkins at IETF <spencerdawkins.ietf@gmail.com>
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Subject: Re: [tsvwg] Robert Wilton's No Objection on draft-ietf-tsvwg-datagram-plpmtud-19: (with COMMENT)
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> On 10 Apr, 2020, at 4:38 pm, Spencer Dawkins at IETF <spencerdawkins.ietf@gmail.com> wrote:
> 
> ISTM that asking people to poke at this and report back in MAPRG is an excellent idea. Depending on whether there are still "relatively few MTU values in use" or not, it might then be useful to consider either updating the table of commonly-used values, or saying "binary search will probably work fine now".

In connection with this, it's perhaps worth noting that some applications won't need to establish the precise MTU, only the minimum number of fragments they need to use for their jumbo datagram.

For example, a 10,000 byte IPv4 packet can fit through a 1500-byte MTU path in seven 1446-byte fragments, but not in six 1684-byte fragments.  (The calculation is different for IPv6 due to the larger headers.)  Refining this distinction further only becomes relevant when datagrams of different sizes have to be sent over the same path, or when a stream transport is involved so that testing specific divisors is not helpful.

So a variety of search algorithms may be useful in different circumstances.

 - Jonathan Morton