Re: Re: ICMP Destination Unreachable Port Unreachable

[Valdis.Kletnieks () vt edu]

On Wed, 16 Aug 2006 12:33:13 BST, Barrie Dempster said:
> Although the port 0 in this case is a red herring and irrelevant. Port 0
> itself when used with TCP/UDP (not ICMP!) can actually be used on the
> Internet. A while back I modified netcat and my linux kernel so that it would
> allow usage of port 0 and was able to connect to a remote machine via TCP
> with that port and communicate fine.

Of course, the poor security geek who see a TCP SYN from port 0 to port 0,
and then a SYN+ACK reply back, will be going WTF??!? for the rest of the day. :)

(Another good one to induce head-scratching is anything that does
RFC1644-style T/TCP.  Anytime you see a packet go by in one direction with
SYN/FIN *and* data, and the reply has SYN/ACK/FIN and data.. ;)
data on it... ;)

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