mtu question

Mark Smith nanog at 85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org
Wed Nov 17 15:48:10 CST 2010


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.




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