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Gateway Address
Addressees are either local or remote. A gateway address is composed of four octets separated
by decimal points. The gateway address is used to uniquely identify the device on the LAN that
has access to the communications links connecting to other LANs, WANs and/or the Internet
(access to the 'remote' addresses).
Virtual Ports
A port number represents a "channel" or entryway for network communications. Port numbers
allow different computers to utilize network resources without interfering with each other. Port
numbers most commonly appear in network programming, particularly socket programming.
Sometimes, though, port numbers are made visible to the casual user. For example, some
websites on the Internet use a URL like the following:
http://www.sitename.com:8100/
In this example, the number 8100 refers to the port number used by the browser to connect to
the web server. The standard port number used by web sites is 80, so this number does not
need to be included with the URL (although it can be). In IP networking, port numbers can
theoretically range from 0 to 65535. Most popular network applications, though, use port
numbers at the lower end of the range (such as 80 for HTTP). Ports are similar to doors and
windows of your house, with port 80 acting as the front door. If these are not open you could
not enter the house. This is the same case with ports on a network. If the ports for a specific IP
address are not open then you could not gain access to that IP address.
Note: The term port also refers to several other aspects of network technology. A port can
refer to Ethernet connection points, such as those on a hub, switch, or router. The term port is
also used to refer to a physical connection point for peripheral devices such as serial, parallel,
and USB ports.
Another analogy would be: if a WAN IP address is similar to the phone number identify a site, IP
ports are similar to telephone extensions, in that they allow communication with specific
devices within a site that all share the same external (WAN) IP address. A router is a device
which allows multiple computers and other IP enabled equipment to share that single WAN IP
address. It functions like a "switchboard operator" – opening ports creates an association
between those port numbers and the LAN IP address of specific equipment on the LAN behind
the router. When the router sees a 'call' for a specific 'extension' (port), it directs that data
stream to the (LAN IP address of the) equipment associated with that 'extension' (port).
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