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WIPA / LIPA: IP Addresses

"IP (Internet Protocol) Address" is a widely used term.

WIPA and LIPA are "my" terms. They stand for...

"WAN IP Address" and "LAN IP Address", "WAN" being another way of saying "Wide Area Network", i.e. "the internet".


A typical LAN IP address (LIPA) starts 192.168. That's followed by two more numbers, both less than 256, separated by periods ("full stops"). So, the following is an example of a full LIPA:

A WIPA also consists of four numbers, each less than 256, separated by periods.


A device on a LAN will have a LIPA. That may be "static", and determined by setting inside the device. Or it may be "assigned to it" by the LAN's DHCP server. If your LAN has some devices configured to use static LIPAs, your LAN's DHCP server needs to have had some blocks of LIPAs set aside for those devices. In other words, the DHCP needs to "know" not to use any of the addresses used by devices which do not ask the DHCP for a LIPA.

"Things" connected to the internet have WIPAs. For the home user, this will fundamentally be their router; it will have a WIPA. And that WIPA will have been assigned to it by the user's internet service provider.

Servers which the home users set up on their LANs may (if everything has been set up properly. (Or if there's been a lapse in setting security high enough!) be accessible from outside the LAN, over the internet.

The visitor from outside the LAN will "see" the server on the LAN as being "at" the router's WIPA.

Routers are Very Clever Bits Of Kit. They take care of passing messages back and forth between users outside the LAN and devices connected locally to the LAN. How does the router know which local device to pass a message to? If the request to connect comes with an explicit statement of the port the outside user wants to connect over, then the router will have been told: "Things arriving for port xx should go to the device at LIPA yy". In some cases, the system can "fall back" to "the usual". For instance, if something "ordinary" comes in from a web browser out there on the internet, the router, absent any other instructions, will send it to the LIPA where it thinks there is a web server, or where it knows there is something set up to handle things arriving for port 80, the default HTTP port. Things for FTP servers default to port 21. But you will often want or need to be explicit about ports, and will sometimes want to set things up to use ports other than the default port for a given service.

Subnet masks

In the work these pages are meant to facilitate, you are sometimes asked to provice a "sub-net mask". I tend to use That seems to take care of my needs without giving rise to problems.

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Sundry general points

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