well, I think I have a new twist on dcc connection troubles, after reading this thread and several other references. If I've somehow missed a crucial explanation, please re-direct me.
After following carefully the instructions for setting up port-forwarding in my DSL router, I restarted two separate copies of the client on two separate computers on my local network. Each computer was the target of a separate range of port-forwarding. Passive mode is disabled.
I verified that the IP addresses seen by each client reflect the true public network address, not the local network.
For reference: the public address is 71.135.xxx.yyy.
My testing was quite straightforward: try both /dcc chat and /dcc send from each computer to the other.
In all cases, when the DCC was initiated, the target computer showed the connect dialogue, but also displayed the origin of the request as being from an unknown address: 220.127.116.11.
Now that completely flummoxes me! I can follow the traceroute completely outside of my ISP's network, so I don't think there is some sort of proxy occurring: I just can't explain the source of this address!
Clearly, something in my configuration (router and/or mIRC) is incorrect, but I just don't see it!
I am also unable to connect with outgoing dcc requests to computers off my local network, and while I can usually successfully receive incoming send requests, sometimes I cannot connect for incoming chat requests, though I can't be certain that the problem is at my end. In those unsuccessful cases I've not been able to verify an incorrect IP address.
I'm totally open to suggestions as to how to proceed to troubleshoot my problems.