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Re: [Int-area] IPv6 fragmentation for IPv4

"Templin, Fred L" <Fred.L.Templin@boeing.com> Tue, 23 May 2017 20:45 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 20:45:41 +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 1:22 PM
> To: Templin, Fred L <Fred.L.Templin@boeing.com>; int-area@ietf.org
> Subject: Re: IPv6 fragmentation for IPv4
> 
> 
> 
> On 5/23/2017 1:13 PM, Templin, Fred L wrote:
> > 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?
> Except for all those devices that look only at the IPv4 header. In that
> case, redefining the IPv4 header this way could interfere with
> mechanisms to manage NAT traversal based based on ID context.

What was it that your document said about the setting of IP ID when
DF=1? Shouldn't it be OK to set the ID to some value of our own
choosing, e.g., a hash of the 5-tuple of the original packet?

> Finally, how do you know when you can even use this? Legacy devices
> could choke on such packets - whether routers or endpoints.

That is a real concern, yes. For the same reason that new transports
like SCTP and DCCP have been proven difficult to deploy. With this
proposal, ip-proto-44 would be just another protocol that middleboxes
block. But, maybe it would work in private internetworks such as
an enterprise network.

Thanks - Fred

> Joe

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