On Jan 16, 2007, at 10:40 AM, Randall Stewart wrote:
"reserved" means one "SHOULD NOT" use that port, where the phrase
in caps is defined in RFC-2119 (http://www.ietf.org/rfc/rfc2119.txt).
[ ...format-flowed quoting trimmed... ]
So let me see if I understand the statements above..
We are using the SHOULD NOT.. which is YOU REALLY REALLY REALLY
REALLY REALLY REALLY should not do this unless you have some
very dramatic demonstrative need to do so and know the FULL
consequences of the action.
Pretty much. :-) If you have a choice about solving the problem in
a way that avoids doing something described as "SHOULD NOT", then one
really ought to prefer that choice.
The bit from wikipedia, while not authoritative in my mind, says you
can send FROM the port, but don't expect an answer back.. which
implies
you cannot bind it and/or cannot read from it if your source
port is 0... Of course in TCP this is totally useless since you
have to get something back in order to setup the handshake.
I don't consider wikipedia to be authoritative either, but it can be
a useful reference or guideline in conjunction with other sources.
Note that there are some uncommonly used TCP variants (T/TCP comes to
mind) where you can short-circuit the 3-way handshake and put actual
data in the initial SYN packet.
I would agree that one SHOULD NOT listen on port 0.
In UDP I guess one could get a packet if the other O/S did not
have any bind restrictions.. or one were to use a raw socket.
Sure, or use BPF/PCAP to generate the packets directly.
But why all this for something you SHOULD NOT DO.. one of the
consequences in my mind of this is that not all O/S's may be
able to read your data .. nor respond to it.
Seems to me a lot of hassle when one can just use a different
port :-0
Well, yes-- there are another 65500+ ports available.
--
-Chuck
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