Lesson 2:?Configuring and Troubleshooting TCP/IP

Each TCP/IP host is identified by a logical IP address that identifies a computer's location on the network in much the same way as a street address identifies a house on a street. Microsoft's implementation of TCP/IP enables a TCP/IP host to use a static IP address or to obtain an IP address automatically from a Dynamic Host Configuration Protocol (DHCP) server. For simple network configurations based on local area networks (LANs), it supports automatic assignment of IP addresses. Windows XP Professional includes tools that you can use to troubleshoot TCP/IP and test connectivity.

After this lesson, you will be able to

• Configure TCP/IP to use a static IP address
• Configure TCP/IP to obtain an IP address automatically
• Explain Automatic Private IP Addressing
• Disable Automatic Private IP Addressing

Estimated lesson time: 60 minutes

Understanding IP Addresses

Each IP address consists of a network ID and a host ID. The network ID, also known as the network address, identifies the systems that are located on the same physical network. All computers in the same physical network must have the same network ID, and the network ID must be unique to the internetwork. The host ID, also known as the host address, identifies each TCP/IP host within a network.

IP addresses are logical 32-bit numbers that are broken down into four 8-bit fields known as octets. Microsoft TCP/IP supports class A, B, and C addresses. The class addresses define which bits are used for the network ID and which bits are used for the host ID. Table 4.4 summarizes class A, B, and C IP addresses.

Table 4.4??Class A, B, and C IP Addresses

Using a Static IP Address

By default, client computers, for example those running Windows XP Professional, Windows 2000, Windows Me, Windows NT, Microsoft Windows 98, or Microsoft Windows 95, obtain TCP/IP configuration information automatically from the DHCP Service. However, even in a DHCP-enabled environment, you should assign a static IP address to selected network computers. For example, the computer running the DHCP Service cannot be a DHCP client, so it must have a static IP address. If the DHCP Service is not available, you can also configure TCP/IP to use a static IP address. For each network adapter card that uses TCP/IP in a computer, you can configure an IP address, subnet mask, and default gateway, as shown in Figure 4.2.

Figure 4.2??Configuring a static TCP/IP address

Table 4.5 describes the options used in configuring a static TCP/IP address.

Table 4.5??Options for Configuring a Static TCP/IP Address

To configure TCP/IP to use a static IP address, complete the following steps:

1. Click Start and then click Control Panel.
2. In the Control Panel window, click Network And Internet Connections.
3. In the Network And Internet Connections window, click Network Connections, double-click Local Area Connection, and then click Properties.
4. In the Local Area Connection Properties dialog box, click Internet Protocol (TCP/IP), verify that the check box to its left is selected, and then click Properties.
5. In the Internet Protocol (TCP/IP) Properties dialog box, in the General tab, click Use The Following IP Address, type the TCP/IP configuration parameters, and then click OK.
6. Click OK to close the Local Area Connection Properties dialog box and then close the Network And Dial-Up Connections window.

Obtaining an IP Address Automatically

If a server running the DHCP Service is available on the network, it can automatically assign TCP/IP configuration information to the DHCP client, as shown in Figure 4.3. You can then configure any clients running Windows XP Professional, Windows 95, and Windows 98 to obtain TCP/IP configuration information automatically from the DHCP Service. This can simplify administration and ensure correct configuration information.

Figure 4.3??A server running the DHCP Service assigns TCP/IP addresses

You can use the DHCP Service to provide clients with TCP/IP configuration information automatically. However, you must configure a computer as a DHCP client before it can interact with the DHCP Service.

To configure a DHCP client, complete the following steps:

1. Click Start and then click Control Panel.
2. In the Control Panel window, click Network And Internet Connections.
3. In the Network And Internet Connections window, click Network Connections, double-click Local Area Connection, and then click Properties.
4. In the Local Area Connection Properties dialog box, click Internet Protocol (TCP/IP), verify that the check box to its left is selected, and then click Properties.
5. In the Network And Dial-Up Connections window, right-click Local Area Connection, and then click Properties.
6. In the Local Area Connection Properties dialog box, click Internet Protocol (TCP/IP), verify that the check box to its left is selected, and then click Properties.
7. In the Internet Protocol (TCP/IP) Properties dialog box, in the General tab, click Obtain An IP Address Automatically.
8. Click OK to close the Local Area Connection Properties dialog box and then close the Network And Dial-Up Connections window.

Using Automatic Private IP Addressing

The Windows XP Professional implementation of TCP/IP supports automatic assignment of IP addresses for simple LAN-based network configurations. This addressing mechanism is an extension of dynamic IP address assignment for LAN adapters, enabling configuration of IP addresses without using static IP address assignment or installing the DHCP Service. Automatic Private IP Addressing is enabled by default in Windows XP Professional so that home users and small business users can create a functioning, single-subnet, TCP/IP-based network without having to configure the TCP/IP protocol manually or set up a DHCP server.

The process for the Automatic Private IP Addressing feature, shown in Figure 4.4, is explained in the following steps:

1. Windows XP Professional TCP/IP attempts to find a DHCP server on the attached network to obtain a dynamically assigned IP address.
2. In the absence of a DHCP server during startup (for example, if the server is down for maintenance or repairs), the client cannot obtain an IP address.
3. Automatic Private IP Addressing generates an IP address in the form of 169.254.x.y (where x.y is the client's unique identifier) and a subnet mask of 255.255.0.0.

Figure 4.4??Automatic Private IP Addressing feature

After the computer generates the address, it broadcasts to this address and then assigns the address to itself if no other computer responds. The computer continues to use this address until it detects and receives configuration information from a DHCP server. This allows two computers to be plugged into a LAN hub to restart without any IP address configuration and to use TCP/IP for local network access.

If the computer is a DHCP client that has previously obtained a lease from a DHCP server and the lease has not expired at boot time, the sequence of events is slightly different. The client tries to renew its lease with the DHCP server. If the client cannot locate a DHCP server during the renewal attempt, it attempts to ping the default gateway listed in the lease.

If pinging the default gateway succeeds, the DHCP client assumes that it is still on the same network where it obtained its current lease, so it continues to use the lease. By default, the client attempts to renew its lease when 50 percent of its assigned lease time has expired. If pinging the default gateway fails, the client assumes that it has been moved to a network that has no DHCP services cur-rently available and it autoconfigures itself as previously described. Once auto-configured, it continues to try to locate a DHCP server every 5 minutes.

Automatic Private IP Addressing can assign a TCP/IP address to DHCP clients automatically. However, Automatic Private IP Addressing does not generate all the information that typically is provided by DHCP, such as the address of a default gateway. Consequently, computers enabled with Automatic Private IP Addressing can communicate only with computers on the same subnet that also have addresses of the form 169.254.x.y.

Disabling Automatic Private IP Addressing

By default, the Automatic Private IP Addressing feature is enabled. However, you can disable it by specifying an alternate configuration to use if a DHCP server cannot be located (see Figure 4.5), as discussed in the next section.

Figure 4.5??Specifying an alternate TCP/IP configuration

Specifying an Alternate Configuration for TCP/IP

Auto-Configuration for Multiple Networks Connectivity provides easy access to network devices and the Internet. It also allows a mobile computer user to seamlessly operate both office and home networks without having to manually reconfigure TCP/IP settings.

You specify an alternate configuration for TCP/IP if a DHCP server is not found. The alternate configuration is useful when a computer is used on multiple networks, one of which does not have a DHCP server and does not use an automatic private IP addressing configuration.

To configure Auto-Configuration for Multiple Networks Connectivity, do the following:

1. Click Start and then click Control Panel.
2. In the Control Panel window, click Network And Internet Connections.
3. In the Network And Internet Connections window, click Network Connections, and then click Local Area Connection.
4. Click Change Settings Of This Connection.

Windows XP Professional displays the Local Area Connection Properties dialog box.

5. Click Internet Protocol (TCP/IP), and then click Properties.

Windows XP Professional displays the Internet Protocol (TCP/IP) Properties dialog box with the General tab active.

6. Click Alternate Configuration.
7. Specify the alternate TCP/IP configuration (see Figure 4.5).

Using TCP/IP Tools

Windows XP Professional includes the tools diagrammed in Figure 4.6, which you can use to troubleshoot TCP/IP and test connectivity.

Figure 4.6??TCP/IP tools included with Windows XP Professional

Troubleshooting TCP/IP

Windows XP Professional offers several tools to assist you in troubleshooting TCP/IP, as described in Table 4.6.

Table 4.6??Tools Used to Troubleshoot TCP/IP

These troubleshooting tools are all executed from within a command prompt. For information about how to use all of these commands, except Hostname and Tracert, open a command prompt, type the command followed by /?, and then press Enter. For example, for information about the Ping tool, open a command prompt, type ping /?, and then press Enter.

To use the Hostname tool, open a command prompt, type hostname, and then press Enter. Hostname returns the name of the local computer.

For information about how to use the Tracert tool, open a command prompt, type tracert, and then press Enter.

Testing TCP/IP Connectivity

Windows XP Professional also provides tools for testing TCP/IP connectivity, as described in Table 4.7.

Table 4.7??Tools Used to Test TCP/IP Connectivity

Testing a TCP/IP Configuration

After configuring TCP/IP and restarting the computer, you should use the Ipconfig and Ping command-prompt tools to test the configuration and connections to other TCP/IP hosts and networks. Such testing helps ensure that TCP/IP is functioning properly.

Using Ipconfig

You use the Ipconfig tool to verify the TCP/IP configuration parameters on a host. This helps to determine whether the configuration is initialized or if a duplicate IP address exists. Use the Ipconfig tool with the /all switch to verify configuration information.

The result of the Ipconfig /all command is as follows:

• If a configuration has initialized, the Ipconfig tool displays the IP address and subnet mask, and, if it is assigned, the default gateway.
• If a duplicate IP address exists, the Ipconfig tool indicates that the IP address is configured; however, the subnet mask is 0.0.0.0.
• If the computer is unable to obtain an IP address from a server running the DHCP Service on the network, the Ipconfig tool displays the IP address as the address provided by Automatic Private IP Addressing.

Using Ping

The Ping tool is a diagnostic tool that you can use to test TCP/IP configurations and diagnose connection failures. After you have verified the TCP/IP configuration, use the Ping tool to determine whether a particular TCP/IP host is available and functional. To test connectivity, use the Ping tool with the following syntax:

ping IP_address

Using Ipconfig and Ping

Figure 4.7 outlines the steps for verifying a computer's configuration and for testing router connections.

Figure 4.7??Using Ipconfig and Ping

The following list explains the steps outlined in Figure 4.7:

1. Use the Ipconfig tool to verify that the TCP/IP configuration has been initialized.
2. Use the Ping tool with the loopback address (ping 127.0.0.1) to verify that TCP/IP is correctly installed and bound to your network adapter card.
3. Use the Ping tool with the IP address of the computer to verify that your computer is not a duplicate of another IP address on the network.
4. Use the Ping tool with the IP address of the default gateway to verify that the default gateway is operational and that your computer can communicate with the local network.
5. Use the Ping tool with the IP address of a remote host to verify that the computer can communicate through a router.

By default, the following message appears four times in response to a successful Ping command:

Reply from IP_address

Practice:?Configuring TCP/IP

In this practice, you'll use two TCP/IP tools to verify your computer's configuration. Then you'll configure your computer to use a static IP address and verify your computer's new configuration. Next you'll configure your computer to use a DHCP server to automatically assign an IP address to your computer, whether or not there is a DHCP server available on your network. Finally, you'll test the Automatic Private IPAddressing feature in Windows XP Professional by disabling the DHCP server, if there is one on your network.

After completing this practice, you will be able to

• Verify a computer's TCP/IP configuration
• Configure TCP/IP to use a static IP address using Automatic IP Addressing
• Configure TCP/IP to obtain an IP address automatically using DHCP
• Determine what happens when there is no server running the DHCP Service to provide an IP address

To complete this practice, you need

• TCP/IP as the only installed protocol.
• Optional: A server running the DHCP Service to provide IP addresses. If you are working on a computer that is not part of a network and there is no server running the DHCP Service, there are certain procedures in this practice that you will not be able to perform.

In the following table, record the IP address, subnet mask, and default gateway that your network administrator provides for you to use during this practice. Ask your network administrator if there is another computer that you can use to test your computer's connectivity, and record the IP address of that computer as well. If you are not on a network, you can use the suggested values.

Run the ConfiguringTCP/IP file in the Demos folder on the CD-ROM accompanying this book for a demonstration of configuring TCP/IP.

Exercise 1: Verifying a Computer's TCP/IP Configuration

In this exercise, you'll use two TCP/IP tools, Ipconfig and Ping, to verify your computer's configuration.

To verify a computer's configuration

1. Click Start and then click Run.
2. In the Run dialog box, type cmd and then click OK to open a command prompt.
3. At the command prompt, type ipconfig /all | more and then press Enter.

   The Windows XP Professional IP Configuration tool displays the TCP/IP configuration of the physical and logical adapters configured on your computer.

4. Press Spacebar as necessary to display the heading Local Area Connection. Use the information displayed in this section to complete as much of the following table as possible. Press Spacebar to display additional information as necessary and to return to the command prompt.

   Local Area Connection setting	Value
   Host name
   Primary DNS suffix
   Connection-specific DNS suffix description
   Physical address
   DHCP enabled
   Autoconfiguration enabled
   Autoconfiguration IP address
   Subnet mask
   Default gateway

5. Press Spacebar as necessary to scroll through the configuration information and return to the command prompt.
6. To verify that the IP address is working and configured for your adapter, type ping 127.0.0.1 and then press Enter.

   A response similar to the following indicates a successful ping:

   Pinging 127.0.0.1 with 32 bytes of data:
   Reply from 127.0.0.1: bytes=32 time<10ms TTL=128
   Reply from 127.0.0.1: bytes=32 time<10ms TTL=128
   Reply from 127.0.0.1: bytes=32 time<10ms TTL=128
   Reply from 127.0.0.1: bytes=32 time<10ms TTL=128
   Ping statistics for 127.0.0.1:
   Packets: Sent = 4, Received = 4, Lost = 0 <0% loss>,
   Approximate round trip times in milliseconds:
   Minimum = 0ms, Maximum = 0ms, Average = 0ms
   

7. Minimize the command prompt.

Exercise 2: Configuring TCP/IP to Use a Static IP Address

In this exercise, you'll configure TCP/IP to use a static IP address.

To configure TCP/IP to use a static IP address

1. Click Start and then click Control Panel.
2. In the Control Panel window, click Network And Internet Connections.
3. In the Network And Internet Connections window, click Network Connections, and then click Local Area Connection.
4. Under Network Tools, click Change Settings Of This Connection.

   The Local Area Connection Properties dialog box appears, displaying the network adapter in use and the network components used in this connection.

5. Click Internet Protocol (TCP/IP), and then verify that the check box to the left of the entry is selected.
6. Click Properties.

   The Internet Protocol (TCP/IP) Properties dialog box appears.

7. Click Use The Following IP Address.
   In the next step, if the computer you are using is on a network, enter the IP address, subnet mask, and default gateway values you recorded in the table in Exercise 1. If you are on a stand-alone computer, complete the next step as it is written.
8. In the IP Address text box, type 198.168.1.201 and in the Subnet Mask text box type 255.255.255.0.
   Be careful when entering IP configuration settings manually, especially numeric addresses. The most frequent cause of TCP/IP connection problems is incorrectly entered IP address information.
9. Click OK to return to the Local Area Connection Properties dialog box.
10. Click OK to close the Local Area Connection Properties dialog box and return to the Network Connections window.
11. Minimize the Network Connections window.

To test the static TCP/IP configuration

1. Restore the command prompt.
2. At the command prompt, type ipconfig /all | more and then press Enter.

   The Windows XP Professional IP Configuration tool displays the physical and logical adapters configured on your computer.

3. Press Spacebar as needed to scroll through the configuration information and locate the local area connection information.
4. Record the current TCP/IP configuration settings for your local area connection in the following table.

   Setting	Value
   IP address
   Subnet mask

5. Press Spacebar as necessary to scroll through the configuration information and return to the command prompt.
6. To verify that the IP address is working and configured for your adapter, type ping 127.0.0.1 and then press Enter.

   If the address is working and configured, you receive the following result:

   Reply from 127.0.0.1: bytes=32 time<1ms TTL=128
   Reply from 127.0.0.1: bytes=32 time<1ms TTL=128
   Reply from 127.0.0.1: bytes=32 time<1ms TTL=128
   Reply from 127.0.0.1: bytes=32 time<1ms TTL=128
   

7. If you have a computer that you are using to test connectivity, type ping ip_address (where ip_address is the IP address of the computer you are using to test connectivity) and then press Enter. Minimize the command prompt.

Exercise 3: Configuring TCP/IP to Automatically Obtain an IP Address

In this exercise, you'll configure TCP/IP to automatically obtain an IP address. You'll then test the configuration to verify that the DHCP Service has provided the appropriate IP addressing information. Be sure to perform the first part of this exercise even if you have no DHCP server because these settings are also used in Exercise 4.

To configure TCP/IP to automatically obtain an IP address

1. Restore the Network Connections window, right-click Local Area Connection, and then click Properties.

   The Local Area Connection Properties dialog box appears.

2. Click Internet Protocol (TCP/IP) and verify that the checkbox to the left of the entry is selected.
3. Click Properties.

   The Internet Protocol (TCP/IP) Properties dialog box appears.

4. Click Obtain An IP Address Automatically.
5. Click OK to close the Internet Protocol (TCP/IP) Properties dialog box.
6. Click OK to close the Local Area Connection Properties dialog box.
7. Minimize the Network Connections window.

To test the TCP/IP configuration

1. Restore the command prompt, type ipconfig /release and then press Enter.
2. At the command prompt, type ipconfig /renew and then press Enter.
3. At the command prompt, type ipconfig | more and then press Enter.
4. Pressing Spacebar as necessary, record the current TCP/IP configuration settings for your local area connection in the following table.

   Setting	Value
   IP address
   Subnet mask
   Default gateway

   To test that TCP/IP is working and bound to your adapter, type ping 127.0.0.1 and then press Enter.

5. The internal loopback test displays four replies if TCP/IP is bound to the adapter.

Exercise 4: Obtaining an IP Address Using Automatic Private IP Addressing

In this exercise, if you have a server running the DHCP Service, you need to disable it on that server so that a DHCP server is not available to provide an IP address for your computer. Without a DHCP server available to provide an IP address, the Windows XP Professional Automatic Private IP Addressing feature provides unique IP addresses for your computer. If the DHCP Service cannot be disabled, simply disconnect your network adapter cable.

To obtain an IP address by using Automatic Private IP Addressing

1. At the command prompt, type ipconfig /release and then press Enter.
2. At the command prompt, type ipconfig /renew and then press Enter.

   There is a pause while Windows XP Professional attempts to locate a DHCP server on the network.

   What message appears, and what does it indicate?

3. Click OK to close the dialog box.

To test the TCP/IP configuration

1. At the command prompt, type ipconfig | more and then press Enter.
2. Pressing Spacebar as necessary, record the current TCP/IP settings for your local area connection in the following table.

   Is this the same IP address assigned to your computer in Exercise 3? Why or why not?

3. Press Spacebar to finish scrolling through the configuration information, as necessary.
4. To verify that TCP/IP is working and bound to your adapter, type ping 127.0.0.1 and then press Enter. The internal loopback test displays four replies if TCP/IP is bound to the adapter.
5. If you have a computer to test TCP/IP connectivity with your computer, type ping ip_address (where ip_address is the IP address of the computer that you are using to test connectivity) and then press Enter. If you do not have a computer to test connectivity, skip this step and proceed to Exercise 5.

   Were you successful? Why or why not?

Exercise 5: Obtaining an IP Address Using DHCP

Before you begin this exercise, you'll need to enable the DHCP Service running on the computer that is acting as a DHCP server (or reconnect your network cable if you disconnected it in Exercise 4). In this exercise, your computer obtains IP addressing information from the DHCP server.

To obtain an IP address using DHCP

1. At the command prompt, type ipconfig /release and then press Enter.
2. At the command prompt, type ipconfig /renew and then press Enter.

   After a short wait, a message box indicates that a new IP address was assigned.

3. Click OK to close the message box.
4. At the command prompt, type ipconfig /all | more and then press Enter.
5. Verify that the DHCP server has assigned an IP address to your computer.
6. Close the command prompt.

Lesson Review

Here are some questions to help you determine whether you have learned enough to move on to the next lesson. If you have difficulty answering these questions, review the material in this lesson before beginning the next lesson. The answers are in Appendix A, "Questions and Answers."

1. Why would you assign a computer a static IP address?
2. Which of the following statements correctly describe IP addresses? (Choose all answers that are correct.)
   1. Logical 64-bit addresses that identify a TCP/IP host.
   2. Each network adapter card in a computer running TCP/IP requires a unique IP address.
   3. 192.168.0.108 is an example of a class C IP address.
   4. The host ID in an IP address is always the last two octets in the address.
3. What is the purpose of a subnet mask?
4. By default, client computers running Windows XP Professional, Windows 95, or Windows 98 obtain TCP/IP configuration information automatically from the DHCP Service: True or false?
5. Which of the following statements about obtaining an IP address automatically are true? (Choose all answers that are correct.)
   1. Windows XP Professional includes the DHCP Service.
   2. Windows XP Professional includes an Automatic Private IP Addressing feature, which provides DHCP clients with limited network functionality if a DHCP server is unavailable during startup.
   3. The Internet Assigned Numbers Authority (IANA) has reserved 169.254.0.0 through 169.254.255.255 for Automatic Private IP Addressing.
   4. You should always disable Automatic Private IP Addressing in small workgroups.
6. Your computer running Windows XP Professional was configured manually for TCP/IP. You can connect to any host on your own subnet, but you cannot connect to or even ping any host on a remote subnet. What is the likely cause of the problem and how would you fix it?
7. Your computer's Computer Name is Pro1 and you ping Pro1. The local address for Pro1 is returned as 169.254.x.y. What does this tell you?

Lesson Summary

• Each TCP/IP host is identified by a logical IP address that identifies a computer's location on the network.
• Microsoft's implementation of TCP/IP enables a TCP/IP host to use a static IP address, to obtain an IP address automatically from a DHCP server, or to use automatic assignment of IP addresses.
• Windows XP Professional does not include the DHCP Service; only the Windows 2000 Server products provide the DHCP Service.
• Computers enabled with Automatic Private IP Addressing can communicate only with computers on the same subnet that also have addresses of the form 169.254.x.y.
• You should use the Ipconfig and Ping command-prompt tools to test the configuration and connections to other TCP/IP hosts and networks.