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To find out if a TCP service is responding, follow these steps:

1.    Choose Start > Run.

2.    Enter telnet and click OK to open the Telnet utility.

3.    Choose Connect > Remote System to open the Connect dialog box:

4. In the Host Name field, type the IP address or DNS host name of the host running the TCP service to which you want to connect.

For example, to find out if a web server is responding to TCP port 80 (its default port), enter the IP address or DNS host name of the web server (, in this case).

5.    In the Port field, enter the number from Table 4.6 that corresponds to the service you want to check.

6.    Click Connect.

If you successfully connect to the web server, you won’t be notified that this is the case. If the web server doesn’t respond, you’ll receive a Connect Failed message.

If you’re attempting to connect to an SMTP server, telnet to port 25, and you’ll see a screen similar to that in Figure 4.14. Theoretically, you could send an e-mail message using Telnet to see if your SMTP system is functioning.

FIGURE 4.14 Using Telnet to find out if your SMTP mail system is responding

The nslookup Utility

^^^henever you are configuring a server or workstation to connect to the Internet, you will always have to configure DNS if you want name resolution to happen (i.e., if you want to be able to type instead of an IP address). When doing this, it is very advantageous to be able to test what IP address DNS is returning to ensure that it is working properly.

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