Port forwarding

From Free net encyclopedia

Image:Port fwd config.png

Port forwarding (sometimes also referred to as tunneling) is the act of forwarding a network port from one machine to another. One use of this technique can allow an external user to reach a port on a private IP address (inside a LAN) from the outside via a NAT-enabled router.

This allows remote computers (e.g. public machines on the Internet) to connect to a specific computer within a private LAN, depending on the port used to connect.

For example:

• forwarding port 8000 on the router to a user's machine allows Shoutcast streaming
• forwarding ports 5000 through 6000 to a user's machine allows the use of Unreal Tournament

Modern Linux machines achieve this by adding iptables rules to the nat table: with target DNAT to the PREROUTING chain, and/or with target SNAT in the POSTROUTING chain.

Some common caveats with port forwarding include:

• the need to forward the packets that come to the router's forwarded port as well as the need to rewrite them so that the machine to which the port is forwarded to can reply to the original source address, which in turn leads to
• the inability of the destination (private) machine to see the actual originator of the forwarded packets, and instead see them as if originating from the router

See also

• Network address translation
• Port triggering
• Secure Shell

External links

• AskMisterWizard.com - Port Forwarding explained for beginners, video links.
• Portforward.com - extensive guide on setting up port forwarding on your router
• Slingbox Port Forwarding Help
• HomeNetMagic Port Mapper - FREEWARE which manages ports and takes care of port forwarding on your Router/Gateway
• testmyports.com - Checks to see if your ports are properly forwarded
• canyouseeme.org - Tells you if your ports are forwarded properly (even ports under 1024)
• How to Map a Port in ICS Using an .inf File, port mapping for Microsoft
• Port Forward Tester - Freeware UDP Port Forward tester for Windows and Linux

Internet Connection Sharing (ICS)

• AnalogX PortMapper
• ICS Configuration, application utility to manage port mapping in ICSde:Port Forwarding

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