TCP/IP Installation Tips

By Rob Wentworth

Reprinted with permission from The Digital Viking
(official newsletter of the Twin Cities PC User Group)
August 1997

When installing networking protocols for older versions of Microsoft Windows 95, Windows NT, and Windows for Workgroups products, the default protocols are IPX and SPX (for Novell NetWare compatibility), and NETBEUI (for NETBIOS compatibility). Additional networking protocols are available, including TCP/IP (Internet Protocol). TCP/IP is not included on the Windows for Workgroups installation disks, but may be downloaded from the Microsoft web site.

Recent versions of Microsoft Windows 95 and Microsoft Windows NT automatically select the default networking protocol as TCP/IP. Other protocols are available, including IPX, SPX, and NETBEUI.

TCP/IP For Modems

When installing TCP/IP for accessing the Internet over a modem, you can just set the IP address to "server assigned IP address", in the dial-up TCP/IP settings. Each time you connect to your Internet Service Provider (ISP), you will be given a temporary "dynamic" IP address from the range of IP addresses owned by the ISP. Each time you connect, you will probably receive a different IP address. While connected, your machine will be the only one in the world using that unique IP address. Because this IP address changes each time you log in, other people will have a difficult time finding your machine to connect to it. If you want your machine to always have the same IP address so other people will be able to find and connect to your machine over the Internet, you will have to purchase a fixed IP address from your ISP (for an extra charge).

TCP/IP for Network Cards

When installing TCP/IP protocol on computers attached to a local-area network (LAN), each machine (actually each network card) on the network must be identified by a unique IP address. An IP address consists of four eight-bit numbers (0-255) separated by "dots" (periods). The IP address "10.0.2.15" is pronounced "ten dot zero dot two dot fifteen". If multiple machines have the same IP address, there is no way to communicate with just one of them.

If your LAN is connected to the Internet and any of your machines is improperly assigned an IP address that belongs to another machine elsewhere on the Internet, you will not be able to access the machine that the IP address really belongs to. Unfortunately, this problem is more common than you would expect, because many systems administrators follow exactly examples given in documentation from Microsoft and others, and this documentation often shows IP addresses that may belong to a machine somewhere on the Internet.

Getting Unique IP Addresses

One way to get unique IP addresses for your LAN is to obtain exclusive ownership of a block of IP addresses, and to assign these addresses to various machines on your network. This is required if your LAN is or will be attached to the Internet, and your machines are to be visible to the outside world. Unfortunately, IP addresses are normally sold in blocks of 256 (or more), and we are running out of available IP addresses, so they are getting rather difficult to obtain for personal use.

You may be able to purchase fixed IP addresses from your ISP, but this can be a little expensive. Also, if you ever switch to a different ISP, your IP addresses will change.

IP Addresses Reserved for Private LANs

If none of your machines needs to be accessible to the outside world, you can assign IP addresses to them from a range of private IP addresses, which are reserved exclusively for that purpose. These IP addresses are guaranteed never to be assigned to any machines on the

There are three blocks of IP addresses reserved for private local-area networks, as defined in the Internet standards document "RFC 1989". These IP address blocks are:

10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255

Resolving IP Address Conflicts

Some short-sighted systems administrators just pull IP addresses "out of thin air", assuming that their LAN will "never" be connected to the Internet, or that the chances of an IP address conflict with any particular Internet site is so remote that it really does not matter to them. More than once, I was unsuccessful trying to convince systems administrators that they were doing it wrong -- a common attitude amongst these guys seems to be "this is how we have always done it, and it works fine for us."

If you are trying to access an Internet site over a LAN and you consistently cannot connect to a site, you may want to very that the IP addresses of all the machines on your LAN are either uniquely owned by these machines, or belong to one of the blocks of IP addresses reserved for private LAN use. If there are problems, you may want to show this article to the system administrator for your LAN.

References

RFC search form: http://www.internic.net/ds/dspg1intdoc.html.
RFC Index: http://www.internic.net/ds/dspg2intdoc.html
RFC 1918: http://www.internic.net/rfc/rfc1918.txt