Re: [Int-area] Discussion about Section 6.1 in draft-ietf-intarea-frag-fragile

Ole Troan <otroan@employees.org> Fri, 06 September 2019 16:34 UTC

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From: Ole Troan <otroan@employees.org>
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Date: Fri, 6 Sep 2019 18:34:33 +0200
Cc: Joe Touch <touch@strayalpha.com>, Ron Bonica <rbonica=40juniper.net@dmarc.ietf.org>, "int-area@ietf.org" <int-area@ietf.org>, IESG <iesg@ietf.org>, Joel Halpern <joel.halpern@ericsson.com>, "draft-ietf-intarea-frag-fragile@ietf.org" <draft-ietf-intarea-frag-fragile@ietf.org>, Suresh Krishnan <suresh@kaloom.com>, "intarea-chairs@ietf.org" <intarea-chairs@ietf.org>
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Subject: Re: [Int-area] Discussion about Section 6.1 in draft-ietf-intarea-frag-fragile
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>>>>> And of course encapsulation can also exacerbate the problem
>>>>> by increasing packet size.
> 
> All this means is that the fragmentation layer needs to take into account the
> size of the outer encapsulation layers that will be added and make sure its
> fragments do not exceed 1280 bytes *after* encapsulation. So, e.g., if the
> encapsulation layer adds an IPv6 header and a UDP header the fragmentation
> layer should not produce fragments larger than 1280 - 40 - 8 = 1232. If the
> fragmentation layer does not know the size of the outer encapsulations to
> be added, it can overestimate and set a safe smaller value (e.g., 1024).

Yes, absolutely. But I don't think we are talking about IP fragmentation any more.

Cheers,
Ole