On a computer that obtains its IP information automatically, type the command

104 | Lesson 5 There is actually no address assigned to the computer at this time. It is known as the IP 0.0.0.0.

b. Type the command ipconfig renew to retrieve an IP address and other IP

configurations. This should reconfigure the computer with the same IP address it used before. If the IP address has only been released for a short time, the renew option will reconfigure the address based on information stored in the registry. If no informa- tion is available or the address has expired after a certain amount of time, the computer will seek out a DHCP server on the network from which to obtain an IP address. These commands can be useful if a new DHCP server has been placed on the network or the current DHCP server has been reconfigured. The commands are also helpful if an error has occurred in the network adapter’s IP configuration, or if APIPA has gotten in the way and has self-assigned a 169.254.0.0 address to the client. The commands issued in step 5a and 5b pertain to IPv4; however, to release and renew IPv6 addresses, simply add a 6 to the option—for example ipconfig release6. More information about this process and DHCP is provided in Lesson 6. 6. Display, flush, and register DNS information:

a. Type the command ipconfig displaydns.

This displays Domain Name System records for the client computer, including localhost connections.

b. Type the command ipconfig flushdns.

This empties the DNS cache.

c. Type the command ipconfig registerdns.

This registers the computer with the nearest DNS server. The last two commands can be useful if there is an error with the DNS configuration on the client, or if a new DNS server or newly configured DNS server becomes live on the network. Figure 5-7 A released IP configuration Implementing TCPIP in the Command Line | 105 As you can see, the ipconfig command has many uses. It can be used to analyze and troubleshoot basic networking connections, as well as to troubleshoot DHCP and DNS issues. Let’s move on to the ping command. Ping is used to test the existence of other hosts on the network. However, there are many permutations of ping. 7. Type the command ping ?. This displays the help file for the command. Note the various options available to you.

8. Ping the local host computer and other computers on the network:

a. Type the command ping localhost.

b. Type the command ping loopback.

c. Type the command ping 127.0.0.1.

The first two commands are basically the same. However, when you ping 127.0.0.1, the results do not include any hostname resolution information. This is the best way to ping the localhost when testing IPv4. When pinging 127.0.0.1, no traffic is placed on the network segment; rather, all traffic is kept inside the computer or local loopback. Now select another computer to ping; it could be a partner’s computer, a secondary computer, or a router. Make note of its IP address. For this example, we will use the address 10.254.254.252. d. Type the command ping [IP address]. For example ping 10.254.254.252. This tests whether another host on the network is live. You can also ping another computer on the network by host name. To find out the host name of a computer, type either the command hostname or the command ipconfig. Examples of pinging an IP address and pinging the corresponding host name are shown in Figure 5-8. Notice the IP address in the first ping 10.254.254.252, as well as the host name server2003 and resolved IP address 10.254.254.252 in the second ping. Disable IPv6 in the Local Area Connection Properties window before continuing with this portion of the exercise. If you get replies that include::1 in the address, then IPv6 is still functioning. TAKE NOTE Figure 5-8 Pinging by IP address and host name If the computer you pinged is alive, the pinging computer will get replies. However, if the computer is not live or is not available, you will get one of several error messages e.g., “Request timed out,” “Destination host unreachable,” or a similar error. When troubleshooting network connectivity issues, start with the local computer and then branch out. For example, start with a ping of 127.0.0.1, then try pinging