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Re: [v6ops] PMTUD issue discussion

"Fred Baker (fred)" <fred@cisco.com> Tue, 26 August 2014 15:14 UTC

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From: "Fred Baker (fred)" <fred@cisco.com>
To: Andrew 👽 Yourtchenko <ayourtch@gmail.com>
Thread-Topic: [v6ops] PMTUD issue discussion
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Date: Tue, 26 Aug 2014 15:13:51 +0000
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Subject: Re: [v6ops] PMTUD issue discussion
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On Aug 26, 2014, at 2:50 AM, Andrew 👽 Yourtchenko <ayourtch@gmail.com> wrote:

> However, the value of 1 causes a large value of MSS to be used,
> resulting in about 1.5 second hiccup. So, yeah it "works" but for
> barely acceptable values of "works"
> 
> Setting the value to 2 causes the initial MSS to be 512, which
> "mitigates" the problem and avoided the hiccups on a 100kb file I was
> testing with - at the expense of almost 3x more packets of course.
> 
> I think it would be useful to see the discussion of this measure and
> its applicability/tradeoffs in the draft.

It seems like it might have value to also test the interaction with various initial window settings, and look at its inclusion in other relevant OS’s including FreeBSD, Windows, and MacOSX. My reading of 4821 says it’s grand theory, but I’m not precisely sure how I would write the code. As an initial setting, for example, I could imagine sending an initial burst containing a 9K byte packet, a 1500 byte packet, and a 1280 byte packet in that order, and set the MSS to the the size of the first acknowledgment I receive. How does that relate to IW=10 (RFC 6928)?

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