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RE: Meta-issues: On the deprecation of the fragmentation function

"Templin, Fred L" <Fred.L.Templin@boeing.com> Tue, 09 July 2013 22:27 UTC

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From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: Carsten Bormann <cabo@tzi.org>, "Manfredi, Albert E" <albert.e.manfredi@boeing.com>
Subject: RE: Meta-issues: On the deprecation of the fragmentation function
Thread-Topic: Meta-issues: On the deprecation of the fragmentation function
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Date: Tue, 09 Jul 2013 22:27:05 +0000
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Hi,

> -----Original Message-----
> From: ipv6-bounces@ietf.org [mailto:ipv6-bounces@ietf.org] On Behalf Of
> Carsten Bormann
> Sent: Tuesday, July 09, 2013 3:08 PM
> To: Manfredi, Albert E
> Cc: ipv6@ietf.org List
> Subject: Re: Meta-issues: On the deprecation of the fragmentation
> function
> 
> > First is, the change of MTU was not one of 576 to 1280.
> 
> I think he was talking about changing the minMTU of Steve Deering's
> Simple IP from 576 first into the mistaken 1500 and then into 1280 in
> the process of turning it into IPv6.
> http://tools.ietf.org/html/draft-deering-sip-00
> (BTW, is that process documented anywhere? RFC1710 doesn't seem to
> mention the MTU.)
> 
> > The other point is, I don't see how transparent adaptation layers are
> an issue at all? I don't think anyone is saying that it's impossible to
> transmit IPv6 over ATM cells? Or are they?
> 
> The problem comes up where the transparency is a leaky abstraction
> (http://en.wikipedia.org/wiki/Leaky_abstraction).
> 
> For ATM, the abstraction was not very leaky as the performance impact
> of sending an MTU-size packet was negligible (at least for the more
> recent cases of ATM).
> 
> For the constrained networks Ran and I are interested in, the
> performance impact of adaptation layer fragmentation can be
> significant, and application layer protocols that get to choose their
> packet sizes can benefit quite a bit if they know this fragmentation is
> taking place and what packet sizes are the thresholds.

I already said in the other thread that aviation and tactical
military links are examples of slow RF links where even as much
as 1280 is asking a lot.

About size issues, the first IPv6 spec (RFC1883) had a 576 minMTU,
and that was changed to 1280 during publication of RFC2460 based
on Steve Deering's Nov. 1997 proposal on the IPng list. Other
sizes of interest:

  68 - real IPv4 minMTU
 576 - de-facto IPv4 minMTU (the one everyone assumes)
 576 - real IPv4 minMRU
 576 - old IPv6 minMTU
1280 - current IPv6 minMTU
1500 - current IPv6 minMRU
1500 - de-facto IPv4 minMRU (the one everyone assumes)
1500 - legacy Ethernet MTU
2048 - proposed new IPv6 minMRU

Fred
fred.l.templin@boeing.com

> Please read the short ALFI draft for more background.
> http://tools.ietf.org/html/draft-bormann-intarea-alfi-03
> http://www.ietf.org/proceedings/85/slides/slides-85-intarea-1.pdf
> 
> Grüße, Carsten
> 
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