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Re: [Int-area] New Version Notification for draft-bonica-intarea-lossless-pmtud-00.txt

Joe Touch <touch@strayalpha.com> Thu, 21 November 2019 05:06 UTC

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From: Joe Touch <touch@strayalpha.com>
In-Reply-To: <8EAB2C81-6BAB-48FE-A25A-469E7770266B@juniper.net>
Date: Wed, 20 Nov 2019 21:06:18 -0800
Cc: "Templin (US), Fred L" <Fred.L.Templin@boeing.com>, "int-area@ietf.org" <int-area@ietf.org>
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References: <81496B9A-2325-47FB-994D-C287CEFFE4D9@juniper.net> <0244fd7b69df4182b4ef250b702a344f@boeing.com> <8EAB2C81-6BAB-48FE-A25A-469E7770266B@juniper.net>
To: Manoj Nayak <manojnayak@juniper.net>
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Subject: Re: [Int-area] New Version Notification for draft-bonica-intarea-lossless-pmtud-00.txt
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> On Nov 20, 2019, at 8:14 PM, Manoj Nayak <manojnayak@juniper.net> wrote:
> 
> Hello Fred,
> 
> Yes, it is possible that the largest fragment received is *much* smaller than the PMTU. However, a survey of 
> popular operating systems reveals that the largest fragment does reflect the PMTU.

That’s great if that’s the only place this ever runs...

> If we are really worried about this problem, the sender can ignore the ICMP message when the MTU is smaller than
> the “smallest believable value” (e.g., 1500 bytes).

I suppose that means you don’t “believe” in tunnels.

Seriously, all this work to get direct report from the endpoint of a packet size that works
- using a protocol that we don’t rely on because it’s generally blocked
- providing a number that might work, if you run on “popular” systems
- all to then throw it out because it isn’t what you “expect”

> There was another query, if it is worth doing Lossless PMTUD for ipv4.
> IPv4 will be with us for a long time. Lossless PMTUD doesn’t take much effort. So why not …

I provided a partial list above.

Joe

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