Lesson 5

Troubleshooting TCP/IP Addressing

2-45

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Figure 2-8

The Internet Protocol (TCP/IP) Properties dialog box

Name Resolution Failures

A common cause of TCP/IP communication problems is a failure to successfully

resolve names into IP addresses. TCP/IP network communication is based on IP

addresses. Every message packet generated by a TCP/IP computer contains a destina-

tion IP address and a source IP address. IP addresses are difficult for human beings to

use and remember, however. As a result, the TCP/IP developers devised services like

DNS and the Windows Internet Name Service (WINS), which enable people to use

friendly names for computers instead of IP addresses.

Name resolution is the process by which a computer converts a name into an IP

address. In the case of DNS names, for example, the computer sends the name to a

DNS server, which replies with the IP address associated with the name. The computer

can then initiate communications using the IP address rather than the name.

If a TCP/IP computer fails to communicate with another computer, it might be because

the name resolution has failed. This means that the two computers are both function-

ing properly; they just don’t have the IP addresses they need to communicate. To test

for a name resolution failure, try to communicate with the destination computer using

its IP address instead of its name. For example, if you are trying to contact a Web server

using the uniform resource locator (URL) http://www.adatum.com/home.html and you

cannot connect, try using the server’s IP address instead of its name, as in the URL

http://10.112.65.34/home.html. If the connection succeeds, the problem lies in the

name resolution.