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DCC

Direct Client-to-Client (DCC) is an IRC-related protocol that is used to transfer data between two clients. DCC CHAT is used for direct chatting without the need to relay messages through the IRC network while DCC SEND is used to send files from one client to another.

DCC works in the following way:

  1. The sender opens a TCP socket on the local computer using a free port number and then sends the IP address along with the port number to the receiver.
  2. The receiver tries to connect to the IP address and port number it got from the sender.
  3. The connection is established and text or data can be transferred.

However, the most common problem for failing DCC connections is that the sender is behind a router and thus doesn't know its external/public IP address. The IP address given in the DCC request is the internal/private address and because it is not routable across the Internet, the receiver is unable to connect. As a result, the DCC connection cannot be established and fails.

Most IRC clients show the IP address they try to connect to. If the address starts with "192.168." or with "10." or less likely with anything in the range from "172.16." to "172.31." it is a private address and as such won't work over the Internet. You should inform the sender about that problem and ask him to fix it.

Conclusion: If the sender has set up DCC in a proper way, DCC will work to any receiver, except for the case where the receiver is not allowed to connect to the Internet without limits (firewall with outgoing filtering, for example).