Re: [Int-area] IPv6 fragmentation for IPv4

"Templin, Fred L" <Fred.L.Templin@boeing.com> Tue, 23 May 2017 18:49 UTC

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From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: Joe Touch <touch@isi.edu>, "int-area@ietf.org" <int-area@ietf.org>
Thread-Topic: IPv6 fragmentation for IPv4
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Date: Tue, 23 May 2017 18:49:28 +0000
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Subject: Re: [Int-area] IPv6 fragmentation for IPv4
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Hi Joe,

> -----Original Message-----
> From: Joe Touch [mailto:touch@isi.edu]
> Sent: Tuesday, May 23, 2017 11:01 AM
> To: Templin, Fred L <Fred.L.Templin@boeing.com>om>; int-area@ietf.org
> Subject: Re: IPv6 fragmentation for IPv4
> 
> 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.

ECMP gateways could be updated to look at the ULP headers
following the IPv6 Frag header in the first fragment.

> IPv6 includes a flow field that serves this
> purpose.

How does it work for plain-old IPv4 fragmentation? I would think
that ECMP gateways would look at the IP ID and try to associate
the fragments so they all get equal ECMP treatment, i.e., the
same as for vanilla IPv4.

Thanks - Fred
fred.l.templin@boeing.com

> Joe