As long as only a small minority of hosts supports >1500-byte MTUs,
there is no incentive for anyone important to start supporting them.
A public server supporting 9000-byte MTUs will be frustrated when it
tries to use them. The overhead (from attempted large packets that
don't make it) and potential trouble will just not be worth it.
This is a little similar to IPv6.
So I don't see large MTUs coming to the Internet at large soon. They
probably make sense in special cases, maybe for "land-speed records"
and dumb high-speed video equipment, or for server-to-server stuff
such as USENET news.
It is *certainly* helpful for USENET news.
So perhaps it is time to chuck the whole thing out and start over. There
seem to be enough projects out there (cleanslate.stanford.edu, etc) that
are looking at just that topic... maybe it is time for a new network
design with IPv6, flexible MTU's, etc.
The existing MTU 1500 situation made sense on ten megabit ethernet, of
course, and at the time, the overall design of the Internet, and the
capabilities of the underlying network hardware were such that it
wasn't that reasonable or practical to consider trying to make it
There is no valid technical reason for that situation with modern
hardware. The reasons people argue against larger MTU all appear to
have to do with hysterical raisins.
1500 was okay at 10 megabits. That could imply 15000 for 100 megabits,
and 150000 for 1 gigabit. There probably isn't a huge number of
applications for such large MTU's, and certainly universal support is
not likely to happen, but we have to realize that the speeds of networks
will continue to increase, and in five years we'll probably be running
terabit networks everywhere. I could picture 150K MTU's being useful
at those speeds.
The goal shouldn't really be to simply allow for some fixed higher MTU.
If any of these "redesign the Internet" programs succeed, we should be
very certain that MTU flexibility is a core feature.