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

"Templin, Fred L" <Fred.L.Templin@boeing.com> Tue, 14 February 2017 19:46 UTC

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From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: "otroan@employees.org" <otroan@employees.org>
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 19:46:06 +0000
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Hi Ole,

> -----Original Message-----
> From: otroan@employees.org [mailto:otroan@employees.org]
> Sent: Tuesday, February 14, 2017 11:17 AM
> To: Templin, Fred L <Fred.L.Templin@boeing.com>
> Cc: Stewart Bryant <stewart.bryant@gmail.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
> 
> Fred,
> 
> >> 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.
> 
> You are correct. "Does not work for IP tunnels without fragmenting the outer header" is what I should have written.
> Of course it appears IPv6 fragments have a order of magnitude higher drop probability than ICMP PMTUD messages.

Right. Depending on the encapsulation, however, fragmentation might occur as
some mid-layer between the outer and inner IP headers. For example, a UDP
encapsulation that includes its own fragmentation control fields. In that way,
the network would only see UDP/IP packets - it would not see IPv6 fragments.

GUE is an example UDP encapsulation that include its own fragmentation
control fields:

https://datatracker.ietf.org/doc/draft-herbert-gue-extensions/

> Pick your poison.

As far as RFC 2473 is concerned, you are right. Other encapsulations that
can do the fragmentation at a mid-layer between the inner and outer
IP headers should be OK.

Thanks - Fred

> Best regards,
> Ole