Re: [v4tov6transition] IPv6 VPNs configured over 1280 MTU tunnels

"Templin, Fred L" <Fred.L.Templin@boeing.com> Mon, 11 October 2010 16:41 UTC

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From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: =?iso-8859-1?Q?R=E9mi_Despr=E9s?= <remi.despres@free.fr>, Washam Fan <washam.fan@gmail.com>
Date: Mon, 11 Oct 2010 09:42:18 -0700
Thread-Topic: [v4tov6transition] IPv6 VPNs configured over 1280 MTU tunnels
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Cc: Softwires <softwires@ietf.org>, "v4tov6transition@ietf.org" <v4tov6transition@ietf.org>
Subject: Re: [v4tov6transition] IPv6 VPNs configured over 1280 MTU tunnels
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> -----Original Message-----
> From: Rémi Després [mailto:remi.despres@free.fr] 
> Sent: Monday, October 11, 2010 9:29 AM
> To: Washam Fan; Templin, Fred L
> Cc: Softwires; v4tov6transition@ietf.org
> Subject: Re: [v4tov6transition] IPv6 VPNs configured over 
> 1280 MTU tunnels
> 
> Hi Washam and Fred,
> 
> Le 9 oct. 2010 à 05:02, Washam Fan a écrit :
> > ...
> > For this bullet in sec5, draft-despres-softwire-6a44-00
> > 
> >   o  6a44 Server functions refuse packets received from their IPv6
> >      pseudo interfaces if their sizes exceed 1280 octets, 
> with ICMPv6
> >      Packet Too Big messages returned to sources as required by
> >      [RFC2460].)
> > 
> > I think it could only apply to the case where the received IPv6
> > packets forwarded to the external domain. In the case the 
> 6a44 server
> > does the hairpinning, the 6a44 server would refuse packets 
> whose size
> > exceed (IPv4 MTU - 28) octets, with ptb ICMPv6 msg.
> > ...
> 
> 
> >>> -----Original Message-----
> >>> From: v4tov6transition-bounces@ietf.org
> >>> [mailto:v4tov6transition-bounces@ietf.org] On Behalf Of
> >>> Templin, Fred L
> >>> ...
> >>> More to this point about double-tunneling, how were
> >>> folks thinking that IPv6 VPNs would be run over a
> >>> 1280 MTU IPv6-in-IPv4 tunnel? That is double-tunneling,
> >>> and seems like it would be a quite common case, but the
> >>> MTU seems deficient. Should it use IPv6 fragmentation?
> >>> ...
> 
> Actually, the 6a44 specification should, instead of 1280, 
> require IPv4 MTU - 28 octets, both for hairpinning and 
> traversal cases.

How can you be sure that IPv4 PMTUD will work in
the traversal case?

Fred

> (It is only hosts that should better take 1280 as default MTU 
> if not having reliable PMTU discovery.)
> I will check with co-authors to fix it in a later version.
> 
> Thanks to both of you for the discussion.
> RD
> 
> 
>