RE: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04

"Templin, Fred L" <Fred.L.Templin@boeing.com> Tue, 14 February 2017 18:55 UTC

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From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: "otroan@employees.org" <otroan@employees.org>, Stewart Bryant <stewart.bryant@gmail.com>
Subject: RE: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04
Thread-Topic: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04
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Date: Tue, 14 Feb 2017 18:54:33 +0000
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Hi Ole,

> -----Original Message-----
> From: otroan@employees.org [mailto:otroan@employees.org]
> Sent: Tuesday, February 14, 2017 10:33 AM
> To: Stewart Bryant <stewart.bryant@gmail.com>
> Cc: Templin, Fred L <Fred.L.Templin@boeing.com>om>; Brian E Carpenter <brian.e.carpenter@gmail.com>om>; gen-art@ietf.org; 6man WG
> <ipv6@ietf.org>rg>; ietf@ietf.org; draft-ietf-6man-rfc1981bis.all@ietf.org
> Subject: Re: [Gen-art] Review of draft-ietf-6man-rfc1981bis-04
> 
> Stewart,
> 
> > *If*  you care about packet loss, then your only option is to probe the path with with
> > synthetic data that exactly mimics the live data, or not to probe at all and live
> > with the 1280. As I said 1280 is pretty close to 1496 which is all most networks
> > will give you in practice.
> 
> Yes, but sending at 1280 does not work for IP tunnels. The whole purpose of the minimum MTU was to give space for tunnel headers
> (1500-1280).

But, if non-tunnel links set a 1280 MTU which is perfectly OK with the standard then
there is no space for headers. Given the issues with classical PMTUD then (plus the
non-applicability of RFC4821 for tunnels) the only solution for tunnels is fragmentation.
I'll let Joe step in if he wants to.

Thanks - Fred

> > When I think about the people asking for fast re-route to minimise packet loss, it seems
> > very strange to deliberately induce loss to try to stretch the MTU by 15%.
> 
> Please show the data that there is significant loss. The measurements I have found has not shown that.
> If not, then let's please leave that argument on the shelf.
> 
> (And please don't read me wrong, I think we should get DNS fixed, that we should fix the IP tunnelling protocols, and that we should
> get IP fragmentation deprecated).
> 
> But right here, right now. PMTUD is for many problems the only solution on the table.
> We as a community can choose not to elevate the standard of course, and that will of course not have any big consequence.
> Are you afraid that elevating 1981, will hinder people from working on new and better solutions?
> 
> Best regards,
> Ole