This is also the case for larger MTU's. This problem is nowhere near non-trivial. Consider e.g. an IPv6 link which is separated by two Ethernet switches, one which supports jumboframes (MTU=9K) and one which does not. How would the hosts be able to, with simple and robust mechanisms, to determine the MTUs to be used on such environment?
This is why we need routers to explicitly advertise the maximum MTU using a new option.
No need for that, already supported now :-).
No, the existing option is only usable for lowering the MTU used within a subnet to a value lower than what the "IP over ..." RFC prescribes. We also need a way to convey the maximum packet size that layer 2 equipment can handle. I think this should be an option that is similar to, but different from the existing MTU option.
It is unlikely that people who need the extra performance gained by the use of jumboframes are also the ones that hook up a $20 switch to a $600 one.
You would be surprised which vendors don't support jumbograms. The bit more expensive ones as well, for example, HP (very widely used around here at least).
Well in that case you have nothing to worry about and stick to 1500 bytes. :-)
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