> I'm not sure this should go into a replacement specification for RFC
> 2461, but I'll bring it up anyway:
>
> Currently, routers can advertise an MTU for a link. That's nice. But
> what we really need is a way for hosts to find out the MTU each
> individual neighbor can handle. 100 Mbps and slower ethernet interfaces
> can typically handle only the standard 1500 byte ethernet MTU, while
> gigabit ethernet interfaces usually support a much larger MTU.
>
> However, in most cases hosts with different MTUs are present on the
> same subnet, so simply advertising a larger MTU wouldn't solve this.
> (Not that this would work anyway as hosts are instructed to only listen
> to MTU advertisements where the MTU is between 1280 and 1500 (for
> ethernet).)
>
> But if hosts can tell each other the MTU they support, each set of two
> hosts is always able to use the largest possible MTU between them.
> (This would also require a new link MTU option that conveys the maximum
> MTU the lower layer equipment supports. Switches have their own MTU and
> even some hubs start doing strange things when a larger than expected
> MTU is used.)
the assumption made in RFC2461 is that the link MTU is constant
over the link, i guess. i don't think it is necessary to make
MTU negotiable between peers, it would complicate too many things.
itojun
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