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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).