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Each host in a LAN has a gateway. A gateway address is composed of four octets
(numbers in the range of 0 to 255) separated by decimal points. The gateway address is
used to uniquely identify a host or computer on the LAN which assigns the IP addresses
to your network. For example, a Linksys router has an IP address of 192.168.1.1. If you
were using this type of router within your LAN, then your gateway would be the IP
address of the Linksys router. The reason this would be your gateway is because the
Linksys is assigning the IP addresses for your network therefore the Linksys would be
the gateway to your network. This is similar to the zip code of your address.
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A port number represents an endpoint or "channel" for network communications. Port
numbers allow different applications on the same computer 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 Web sites a person visits on the
Internet use a URL like the following:
http://www.company.com:8100/
In this example, the number 8100 refers to the port number used by the Web browser to
connect to the Web server. Normally, a Web site uses port number 80 and this number
need not 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 low end of the range (such as 80 for HTTP). This could be similar to
the front door of your house. Without the door to the house being open you could not
enter it. 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 or what it is
addressing.
Note: The term port also refers to several other aspects of network technology. A
port can refer to a physical connection point for peripheral devices such as serial,
parallel, and USB ports. The term port also refers to certain Ethernet connection
points, such as those on a hub, switch, or router.
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