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Re: [tcpm] 793bis: IP ID

Joe Touch <touch@strayalpha.com> Thu, 23 January 2020 01:08 UTC

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From: Joe Touch <touch@strayalpha.com>
In-Reply-To: <a7080caa-18ce-94ec-3bbf-ae5c8d1bc17c@si6networks.com>
Date: Wed, 22 Jan 2020 17:08:12 -0800
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References: <5D669BDA.3000506@erg.abdn.ac.uk> <5D66A044.3060904@erg.abdn.ac.uk> <f4d75224-d7d0-002b-2bca-f93505d6c9d3@mti-systems.com> <4D99C7DD-F57E-4708-8F02-824EB4BF8E24@weston.borman.com> <333A2AF9-7DDD-4FAA-B0BD-E6871564850F@strayalpha.com> <F9E41A50-83FA-477C-8E19-5CE6A58931D3@weston.borman.com> <a7080caa-18ce-94ec-3bbf-ae5c8d1bc17c@si6networks.com>
To: Fernando Gont <fgont@si6networks.com>
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Subject: Re: [tcpm] 793bis: IP ID
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> On Jan 22, 2020, at 11:05 AM, Fernando Gont <fgont@si6networks.com> wrote:
> 
> On 20/12/19 17:37, David Borman wrote:
>> Yes, the IPID is only used for doing IP fragment reassembly, so the IPID really doesn’t matter on retransmission when IP fragmentation is not possible.
> 
> Some boxes are know to clear DF and fragment packets. That's why some implementations have resorted to ensure IP ID uniqueness (or try to), even when they send packets with DF=1.

True, but equally true that devices reuse the ID when the packet is atomic (not already fragmented and DF=1), as noted in RFC 6864. That RFC deprecated use of the IPv4 ID except for reassembly.

There is no similar deprecation of the need for intermediate devices to honor DF.

Joe

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