Lesson 2: Troubleshooting Connectivity Issues

341

Quick Check Answer

■ Check that the computer is set to receive its TCP/IP configuration dynamically. It

has not been reconfigured by DHCP on the WAP and its previous owner has prob-

ably configured it statically with the 10.1.10.231 address. You need to reconfigure

the computer to receive its TCP/IP settings dynamically.

If you want to reconfigure IP settings on a workstation on your network, you can reboot it. If

this is not convenient, the commands ipconfig /release and ipconfig /renew release the old

configuration and obtain a new one. (In theory, ipconfig /renew should be sufficient, but I

always use both commands.) Sometimes when you renew a computer’s configuration, it does

not immediately register its new settings in DNS and you cannot ping it by computer name. In

this case, ipconfig /registerdns forces registration.

NOTE

Opening the administrator Command Prompt Console

The ipconfig /registerdns and ipconfig /flushdns commands require that you run the Command

Prompt Console as an administrator. To do this, select Accessories from the All Programs menu,

right-click Command Prompt, and click Run As Administrator. As with all administrator level

prompts, the UAC dialog box will, by default, prompt you to provide administrator credentials or

click Continue.

If you try to ping a computer by name or access a website from a workstation and DNS cannot

resolve the computer name or URL, then information that resolution has failed is stored

(cached) in the workstation. If you try to do the same thing again, the workstation will not

attempt to obtain name resolution but will instead use the cached information and again fail

the request. This is known as negative caching. However, name resolution might have failed

because of a temporary glitch in the internal or external DNS service. Even though DNS is now

working, the computer name or FQDN will not be resolved to an IPv4 address because of the

cached information. The problem will disappear in 30 minutes or so because the worksta-

tion’s DNS resolver cache is regularly cleared. However, if you do not want to wait this long,

you can solve the problem immediately by using the ipconfig /flushdns command to flush

the DNS cache.

NOTE

The /allcompartments switch

If you use the /allcompartments switch after the ipconfig command, you can apply the command

to all network adapter compartments—that is, universally across all interfaces. For example,

ipconfig /allcompartments /all or ipconfig /allcompartments /renew.

If you want to trace the route of an IP datagram through an internetwork (a series of networks

or hops), you can use the tracert command to list the path the datagram took and the delays

encountered at each hop. To generate the tracert output, shown in Figure 7-25, the command