NAT is a system of translating an IP address used within an internal network to a different IP address used on another, outside network. DSL routers may use NAT to direct incoming connections on your DSL line to a server running on a computer on your local network.
For specific instructions on setting up your router to do NAT (also called "Port Forwarding" or "Virtual Server" on some routers), see the DSL Support page for your router.
Services and Ports
| Service or Application | Ports | Notes |
|---|---|---|
| DNS Server | 53 tcp 53 udp | |
| Telnet Server | 23 tcp | On a Cisco 675 or 678 DSL router, you will also need to enter the command "set telnet disabled" |
| SSH Server | 22 tcp | |
| E-mail (SMTP) Server | 25 tcp | |
| E-mail (POP) Server | 110 tcp | |
| E-mail (IMAP) Server | 143 tcp 143 udp | |
| USENET (NNTP) Server | 119 tcp | |
| FTP Server | 20 tcp 21 tcp | |
| Web (HTTP) Server | 80 tcp | On a Cisco 675 or 678 DSL router, you will also need to enter the command "set web disabled" |
| Secure Web (HTTPS) Server | 443 tcp | |
| IRC Server | 6667 tcp | |
| Shoutcast Server | 8000 tcp | |
| Network Time (NTP) Client | 123 tcp 123 udp | |
| AppleShare | 548 tcp | |
| Quicktime 4 Streaming | 554 tcp 6970-6999 udp | Configure Quicktime to use TCP port 554. |
| RealPlayer Client | 6970 udp | |
| RealPlayer G2 Client | 7070 udp | |
| IRC Client (ident) | 113 tcp | |
| IRC Client (DCC) | The DCC (direct client to client) protocol used by many IRC clients does not work on a standard port number or range of ports, and probably cannot be made to work through NAT (unless your router supports wildcard NAT entries or something similar). | |
| ICQ Client | 2300-2320 tcp 4000 udp | On a Cisco 675 or 678 DSL router, you will also need to enter the command "set nat timeout udp 360" |
| MSN Messenger | 1863 tcp | Not all versions and configurations of MSN Messenger require this port to be open. Do not open this port unless you cannot login using Messenger. |
| NetMeeting Client | 389 tcp 522 tcp 1503 tcp 1720 tcp 1731 tcp | |
| GRE Packets | 0 47 | GRE (generic router encapsulation) is a tunneling protocol used
to create virtual networks. On a Cisco 675 or 678 DSL router, this requires CBOS version 2.1.0 or later. To enable support for GRE packets on all ports, add a NAT entry for port "0" and type "47". |