Re: [Int-area] IPv6 fragmentation for IPv4

Joe Touch <touch@isi.edu> Tue, 23 May 2017 18:01 UTC

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To: "Templin, Fred L" <Fred.L.Templin@boeing.com>, "int-area@ietf.org" <int-area@ietf.org>
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From: Joe Touch <touch@isi.edu>
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Date: Tue, 23 May 2017 11:00:40 -0700
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Subject: Re: [Int-area] IPv6 fragmentation for IPv4
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Hi, Fred (et al.),

On 5/23/2017 9:17 AM, Templin, Fred L wrote:
> Joe, I wanted to run an idea by you. We all know that IPv4 fragmentation has
> problems because of the 16-bit ID field. So, why not insert an IPv6 Fragment
> Header between the IPv4 header and the upper layer protocol data, then
> use IPv6-style fragmentation instead of IPv4 fragmentation?

IPv4 fragmentation has several impediments:
    - small ID field
    - lack of a reassembly checksum
    - lack of a fixed-location flow ID

Using IPv6-Frag as the next header solves only the first of these. The
last is significant - putting a new header would defeat IPv4 flow ECMP
even for the first fragment. IPv6 includes a flow field that serves this
purpose.

Joe