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RFC 1631: When a significant part of the Internet is connected behind...

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Comment by talkol
Submitted on 10/21/2005
Related RFC: RFC 1631
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When a significant part of the Internet is connected behind a NAT many problems are introduced to current client-server architectures. One of the main issues is the ability to listen to incoming connections in an internal computer (behind the NAT). Since only the external NAT IP is advertised on the Internet, the NAT itself must decide to which internal address the incoming packets should be forwarded.The issue of incoming packet forwarding is handled by most NAT implementations today by manual configuration. The user behind the NAT must configure a TCP/UDP port on the NAT which will always be forwarded to a specified internal address. This mechanism proves too difficult for most home users. As a result, most software today requiring incoming connections (such as VoIP, P2P, Messenger) attempts to overcome this by unnatural client-server architectures or centristic designs which were otherwise distributed.A possible solution to incoming packet forwarding issue is to include an IP option field with the internal address behind the NAT. The NAT device, accepting such packet, will inspect this field and use it to forward the packet into the internal segment.Another issue requiring treatment is how the internal IP is known in the Internet to external clients. This is left for the application developers. When a client behind a NAT registers at some central authentication server, the internal IP will also be given. This simplifies many of the current creative solutions meant to solve this problem.Tal Koltalkol@gmail.com

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