RE: Tunnel MTU

["Templin, Fred L" <Fred.L.Templin@boeing.com>]

Iljitsch,

> -----Original Message-----
> From: Iljitsch van Beijnum [mailto:iljitsch@muada.com]
> Sent: Tuesday, July 28, 2009 11:04 AM
> To: Mark Townsley
> Cc: Templin, Fred L; IPv6 Operations
> Subject: Re: Tunnel MTU
> 
> On 28 jul 2009, at 19:44, Mark Townsley wrote:
> 
> > I'd like to clarify of course that some of the MTU issues we
> > discussed were not specific to tunneling, but to mismatched MTUs on
> > a home LAN vs. WAN interface in general.
> 
> In IPv6 you can easily broadcast your WAN MTU in RAs on the LAN. So if
> your WAN has 1337 you simply have an MTU option with "1337" in RAs
> that are sent out on the LAN side.

Not good unless you want to dumb down the MTU on the
LAN side even for communications local to the home
network.

> > The extra 20 bytes of a 6rd or 6to4
> 
> With 6to4 most implementations simply use 1280.

...and *pray* that it won't fragment.

> > encapsulation isn't significant when trying to solve support of 9K
> > jumbo frames and standard 1500 byte ethernet MTUs in the same
network.
> 
> I have an expired draft that solves exactly that issue:
> 
> http://tools.ietf.org/html/draft-van-beijnum-multi-mtu-02
> 
> I intend to bring it back to life in a much improved incarnation at
> some point, didn't get that done before this meeting.

Is it going to require updates to all routers and hosts,
as well as IPv6 specs to be updated?

Fred
fred.l.templin@boeing.com