Re: [Int-area] IPv6 fragmentation for IPv4

"Templin, Fred L" <Fred.L.Templin@boeing.com> Tue, 23 May 2017 20:13 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 20:13:13 +0000
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Subject: Re: [Int-area] IPv6 fragmentation for IPv4
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Joe,

> -----Original Message-----
> From: Int-area [mailto:int-area-bounces@ietf.org] On Behalf Of Templin, Fred L
> Sent: Tuesday, May 23, 2017 11:49 AM
> To: Joe Touch <touch@isi.edu>; int-area@ietf.org
> Subject: Re: [Int-area] IPv6 fragmentation for IPv4
> 
> 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>; 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.

Here's another think - since the IPv6 Frag Header already has a
32-bit IP ID that we are using for fragmentation, and since we
are asking the IPv4 header to set DF=1, the 16-bit IP ID field in
the IPv4 header is available for use as a flow field - right?

Thanks - Fred

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