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

Rémi Després <remi.despres@free.fr> Mon, 11 October 2010 16:28 UTC

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To: Washam Fan <washam.fan@gmail.com>, "Templin, Fred L" <Fred.L.Templin@boeing.com>
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Subject: Re: [v4tov6transition] IPv6 VPNs configured over 1280 MTU tunnels
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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.
(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