absolutely not infected...

this is where it starts to get weird, because I read and thought I'd understood the operation of the DCC protocol....

running Ethereal on the source and destination computers on my local network, as well as Windows Network Monitor on the server that provides a DNS resolver showed the following:

for a DCC CHAT request
1. originating CLIENT sends a NOTICE to the IRC SERVER with a brief message giving the destination NICKNAME, "DCC CHAT" and the destination CLIENT IP address in dotted decimal form enclosed in parentheses, for example
"NOTICE test-nick DCC CHAT ("

2. that is followed immediately (next TCP packet) with a PRIVMSG to the IRC SERVER with a brief message giving the destination NICKNAME, "DCC CHAT chat" followed by the decimal value of the destination CLIENT IP address, and the PORT number to use, for example
"PRIVMSG test-nick DCC CHAT chat 1200058666 54018"

3. the IRC SERVER then passes these two packets to the destination CLIENT for processing -- the destination CLIENT PORT number used is NOT in the DCC PORT range.

4. the destination CLIENT displays the expected dialog box about an incoming chat request, but when the Accept button is pressed, nothing happens, including NO messages on the wire, eventually the attempt times out at the requesting end.

Okay, any thoughts on what to look for next?

To be certain, I loaded fresh copies of mIRC and reinstalled, double-checking to avoid inadvertently making any changes to the DCC defaults, other than the port range to match my router.

This is still a puzzlement, wrapped in an enigma....

Last edited by Richard_B; 07/06/10 10:22 PM.