On 6to4 gateway and recommended MTU setting

Erik Kline ek at google.com
Thu Mar 11 12:56:53 CET 2010

On 11 March 2010 20:40, Martin Millnert <martin at millnert.se> wrote:
> Hello list,
> was discussing best 6to4-relay interface MTU size with a friend and
> basically need more and wiser input.
> Apparently, Free BSD has a unmodifiable, static value of 1280 for the
> 6in4-interface. It could be argued that this follows 4213 3.2.1
> ( http://tools.ietf.org/html/rfc4213#section-3.2.1 ). OSX also has a
> static value of 1280, unmodifiable (I try to stay away from OSX, could
> this be due to the kernel being the same?). XP reportedly also defaults
> to 1280, and I see my Windows 7-box does the same for 6to4, which
> appears once I deactivate native IPv6 on my LAN interface  (netsh
> interface ipv6 show subinterfaces).
> Linux on the other hand defaults to 1480, but it is changeable.
> A working PMTUd will resolve MTU problems, both on underlying IPv4 node
> <-> 6to4-gateway, but this isn't the issue at the moment.
> The issue is what MTU value a single random 6to4-gateway today should
> have (purposefully not considering "the whole"), to maximize good
> interoperability and minimize problems.
> I'm not really concerned with the values of a end-node's 6to4 interface.
> I am not satisfied by the reasoning in 4213#3.2.1 in this regard, hence
> this mail. 3.2.1 to me doesn't seem to talk about a the MTU value of the
> interface on a globally announced relay gateway.
> Cheers,
> Martin

Not to be too snarky, but how about 0?  Just let 6to4 die.  Please,
please, please don't waste any time with 6to4.

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