LIS Notes: Figuring out your IP address.

Figuring out your Internet Protocol (IP) address.

An IP number is like a phone number - it allows machines on the Net to contact each other.  An IP address consists of four groups of numbers (called "octets") separated by periods, each group containing a number between 0 and 255.

If you wish to set up two way or multi way video conferencing using programs like Microsoft NetMeeting, you may find it useful to know your IP number, and those of people to whom you wish to speak. As well, you may wish to know your machine's IP number for diagnostic purposes - for example, if you are trying to debug a Local Area Network (LAN) in your office.

If you are using a Microsoft Windows machine, you can use a utility program called "WINIPCFG" to find out your current  IP number.

If no icon for the WINIPCFG program (pronounced "Win IP Config") on your desktop or in your task bar or startup menus, you can still run the program easily.

From the "start" menu, click "run".
When the dialog box appears, type: C:\WINDOWS\WINIPCFG.EXE
Touch "enter".

You should see a display entitled "Ethernet Adapter Information".
There may be several choices of displays, and you can select them by pressing the small down-arrow beside the display window. For our purposes, the most important elements are:

IP Address: this is the IP number of your computer.
Default Gateway: this is the IP number through which you connect to the rest of the Internet.

Imagine you work in an office, in which all phones are connected via a switchboard or "centrex" to the outside world. The "default gateway" is like the centrex, and your IP number is like your office phone number.

If you reach your Internet Service Provider (ISP) by dialup modem, you will be assigned a temporary IP number each time you connect to the service. The ISP maintains a pool of numbers, and assigns them to users each time they connect. When the user hangs up, the number becomes available for another user. This technique allows many people to share a comparatively few IP numbers. Numbers assigned this way are called "dynamic" rather than "static" IP numbers, because they are apt to change.

If your machine is connected to a Local Area Network (LAN) within an office or computer lab, it will probably be assigned a "static" or unchanging IP. Next time you check, you will most likely find the machine's IP number has not changed, unless the systems administrator has altered it deliberately.

If you use a cable modem, you will likely be assigned a dynamic IP number. However, you will find that the number changes very infrequently - most often after there has been a problem with the network. This is because dynamic numbers can have long "keep alive" dates - normally, they won't be changed for months. This is handy if you communicate by video conferencing, because it lets your friends put your IP in a directory of frequently called machines.

Since hackers know about dynamic and static IP numbers, they may consider it desirable to compromise a machine with a cable or DSL connection, or one on a LAN. Risk to such machines can be minimized by installing good anti-virus software, and perhaps a "firewall". Machines on the Net talk to one another constantly, but a firewall can block specific types of uninvited signals, such as requests to allow a visitor to run various programs on your computer.

Security programs can save you much frustration, but it is much more important, in the long run, that you make backup copies of important documents. Several media are available: for instance, floppy disks, tapes, Zip disks, or CDROMs. Keeping copies on a second machine is another option. Preferably, the second machine should not be connected to the Net, so it won't be compromised. Deliberate hacks are relatively unlikely - it's far more likely that you might wreck your work by accident. Backups are still the best protection.

If you are using a UNIX or Linux system, you can use the shell command netstat -n | more to display the first few network connections. The "local" column will contain your machine's IP number.