If set to zero (default): DCC requests are sent with the first available TCP port, as judged by your operating syste. If set to nonzero: All dcc requests you send will be sent with the TCP port you specified. In this case, note these: - You can only have one listening connection open for the same port at time. After the connection has been established, you can reuse the port again for new connections. - Allowed port range is 1..65535. - Ports 1..1023 are reserved for system services (root-only).
This setting might be handy to circumvent a strict firewall. Together with /set dcchost, most firewall-related problems are history. ;)
See also: set/dcchost dcc/chat dcc/send