mtu question

Wed Nov 17 21:57:13 UTC 2010

Thanks for the 411 Mark!

Again, this NANOG list is such a valuable source of info and knowledge!

> Date: Thu, 18 Nov 2010 08:18:10 +1030
> From: nanog at 85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org
> To: brandon.kim at brandontek.com
> CC: jbates at brightok.net; deric.kwok2000 at gmail.com; nanog at nanog.org
> Subject: Re: mtu question
> 
> On Wed, 17 Nov 2010 16:23:54 -0500
> Brandon Kim <brandon.kim at brandontek.com> wrote:
> 
> > 
> > Jack brings up a good point. MTU is basically pointless since packets never traverse any real interface.......
> > So in theory the size can be anything...
> > 
> > 
> 
> Not quite. You hit packet length field limits. IPv4 packets can't be
> larger than 65535, and IPv6 packets also can't be larger than 65 576
> (40 byte IPv6 header + 2^16 payload), unless the jumbograms and the
> jumbo payload extension header is supported. Last time I checked, by
> setting the loopback MTU > 65 576, Linux, for example, doesn't support
> the jumbo payload extension header (or if it does, I didn't spend
> enough time finding out how to switch it on - a very large MTU didn't
> trigger it).
> 
> That being said, with a 64K MTU on loopback, you can legitimately claim
> to get >10Gbps at home, as long as you don't mention how you're doing
> it ;-)
> 
> Regards,
> Mark.