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Re: [v6ops] PMTUD issue discussion

"Fred Baker (fred)" <fred@cisco.com> Thu, 04 September 2014 20:22 UTC

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From: "Fred Baker (fred)" <fred@cisco.com>
To: Tom Perrine <tperrine@scea.com>
Thread-Topic: [v6ops] PMTUD issue discussion
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Date: Thu, 04 Sep 2014 20:22:43 +0000
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Subject: Re: [v6ops] PMTUD issue discussion
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On Sep 3, 2014, at 6:22 AM, Tom Perrine <tperrine@scea.com> wrote:

> What MTUs are actually (commonly) seen in the wild?
> 
> I can only think of less than a dozen that I would expect to see, assuming that the actual MTU is based solely on the underlying network technology.

There are a number of magic numbers in the literature, notably the values in RFC 2470, which is for IEEE 802.5 Token Ring. As a practical matter today, I think the magic numbers are 1500 and 9000, and those numbers reduced by the sizes of various encapsulations. I’m not quite sure of the math that led us to select the number 1280, but I’ll certainly agree that any encapsulation I can readily think of would work with a packet of that size.

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