mtu question

Mark Smith nanog at
Wed Nov 17 15:48:10 CST 2010

On Wed, 17 Nov 2010 16:23:54 -0500
Brandon Kim < at> 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 ;-)


More information about the NANOG mailing list