Theodore Ts'o writes:
There are a lot of really dumb, dumb, dumb firewall authors out there,
that's why....
Actually, Sally Floyd's explanation makes a lot more sense.
The dumb authors, I think, are those who built Linux implementations
that doggedly attempt to negotiate ECN and are unprepared for cases
where it does not work, even though it's unreasonable to assume that the
entire world is equipped to handle ECN or that all other hosts will
cheerfully ignore the setting of bits that are supposed to be zero. In
this context, Linux is beginning to remind me of Netscape in the early
days.