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Network Working Group P. Srisuresh Request for Comments: 2663 M. Holdrege Category: Informational Lucent Technologies August 1999 IP Network Address Translator (NAT) Terminology and Considerations Weiterlesen
A port is a channel on a machine, that can be used for communication. There are 65536 different ports (0-65535). Some are standarized, that means they are bound to a given defined task, like the mail ports, web ports, and others…
All other ports can be used as one sees need.
Knowledge of ports is important for the configuration of the firewall, to open required ports and close the rest. Communication over a port requires the port to be open.
Therefore it is useful to know the standarized ports and ports required by some programs.
NAT stands for Network Address Translation, and describes the (controlled) change of IP address and/or port. It is usually performed when trying to connect computers on a local network to the Internet. NAT was defined in RFC 2663.
As long as both communication partners are located in the same network, data can be transmitted directly via routers. For data exchange with the public network, one needs a public IP address, either permanent or dynamically assigned by the access providers. It is necessary, as a remote server needs to know where to send the reply.
The assignment of addresses using DHCP requires a DHCP server. This can be a separate device, but is often a program or system service on a computer in the network. This server is started at the first or runs continuously. A network can be managed by multiple DHCP servers.
The number is 48 bits or 64 bits long and is in hexadecimal notation, represented byte for byte. The first 24 bit carry a description of the manufacturer, the other 24 bits or 40 bits carry a manufacturer-numbering (or serial). Its usage is described in RFC 5342.