[Spud] on trust and lying

[Eliot Lear <[e-mail]>]

A comment was made at the microphone that middle boxes will lie to end
hosts and end hosts will lie to middle boxes.  That is not strictly
true, and we have an existence proof of when it is not: that is TCP. 
The intended point of Joe's slide to map SPUD states to TCP wasn't just
a simple example.  The behavior of TCP on the hosts can be observed by
the middle box and based on that behavior the middlebox can make
appropriate decisions.  The most classic example of this is simply
blocking inbound SYNs to block opening of new connections.  New
connections do not establish absent that first naked SYN.  Similarly,
the network can assume that only connections that are already open will
contain an ACK, knowing that a host will reject an unsolicited packet
that contains that flag.  That three way handshake is in effect an
implicit behavior contract between the end host and middle boxes.

Whatever SPUD becomes, it has to establish, at the very least, that
implicit behavior contract for UDP.  Today it simply doesn't exist in
the general sense, although there are may be a higher few protocols that
allow for that.

Eliot