Troubleshoot Resource Access and Connectivity Issues (part 1) - Troubleshooting TCP/IP Configuration

• Mismatched workgroup settings

• Incorrect TCP/IP address configuration

• Incorrectly configured or corrupt name resolution services

• Misconfigured Windows Firewall settings

• Misconfigured network hardware

Because the focus of this book is an enterprise desktop, the following sections look at TCP/IP addressing, name resolution issues, and Windows Firewall configuration issues.

Troubleshooting TCP/IP Configuration

Within an enterprise Windows Vista desktops are most likely configured to use automatic IP configuration or DHCP. A Windows Vista computer utilizes the DHCP client service to acquire its IP configuration information from a DHCP server. The following sections look at troubleshooting TCP/IPv4 and TCP/IPv6 address acquisition.

Troubleshooting TCP/IPv4 Addressing and TCP/IPv6 Addressing

Several factors may contribute to a Windows Vista computer failing to acquire a DHCP address. If a Windows Vista computer is configured with an IP address in the 169.254.x.y/16 address space, that Windows Vista computer is unable to acquire a DHCP address. The DHCP client service on the computer attempts every five minutes to acquire an IP address. The following are some of the first items you need to check when troubleshooting a DHCP client’s inability to acquire a DHCP address:

• Check to see if the Windows Vista configuration of the network interface for the TCP/IPv4 properties is selected and set to Obtain an IP Address Automatically.
  
  
• Check to see whether other desktops on the local network are also unable to acquire a DHCP address. If so, ensure that a DHCP server is up and running.
  
  
• If this computer is the only one not receiving a DHCP address, check to see if the DHCP client service needs to be started or possibly restarted.
  
  
• Check to see whether the DHCP server is on the local subnet of the Windows Vista computer. If so, ensure that adequate IP addresses are left in the DHCP scope for the subnet.
  
  
• If the DHCP server is on a remote network, ensure the local subnet has an RFC 1542-capable router with the interface connected to the Windows Vista desktop configured to relay DHCP broadcasts to the appropriate DHCP server.
  
  

Restarting the DHCP client service has been found to work in some instances in which it appears that a single Windows Vista computer is unable to receive a DHCP address. It is just good troubleshooting in this case to restart the DHCP client service and ensure it is set to start automatically. It is also possible a recent patch or update was installed and the computer itself may require a restart or, at the very least, a restart of the DHCP client service. Figure 1 shows the Services Microsoft Management Console (MMC) and an administrator attempting to restart the DHCP client.

Figure 1. The Services MMC displaying how to restart the DHCP client service.

In addition, if the DHCP scope has had an alteration to an item or has been deleted and redone, the client requires the DHCP configuration to be relearned. To do this, a user could easily reboot the computer, but that involves far too much loss of time for a simple procedure—although it is usually easier to tell the user over the phone to just reboot. Another method would be to have the user go to a command line and enter the command ipconfig /all to review the DHCP information. And one more method is to view the status of a network connection in the Network and Sharing Center, select to view the status, and then select the details of the connection. Figure 2 shows the output of these steps.

Figure 2. Viewing the details of a network connection.

From this output, you are also able to determine the DHCP server where the client is receiving its DHCP IP configuration. This particular client is receiving its DHCP information from the DHCP server located at 10.1.0.4.

If, after contacting the DHCP administrator, it has been determined that the DHCP information on the local Windows Vista client is stale, you can attempt to refresh the DHCP configuration on the client by entering at the command line in the order listed here in the following two commands:

ipconfig /release

The preceding command drops all DHCP-related IP configuration from all its network interfaces because no specific interface is listed in the command.

ipconfig /renew

The preceding command requires all network interfaces set to obtain their IP configuration automatically to broadcast a request for a DHCP server for DHCP configuration information through their wired or wireless connection. Any new or modified DHCP configuration options in the scope are acquired, or a newly constructed scope with different DHCP scope options is acquired.

Releasing and renewing the IP configuration information on an adapter using the ipconfig command releases DHCP IP configuration for IPv4. To release or renew DHCPv6 IP configuration, you need to use commands that are somewhat modified for this particular function. These modified commands are as follows:

ipconfig /release6
ipconfig /renew6

IPv6 Autoconfiguration IPv6 autoconfiguration utilizes two different sets of services for automatically acquiring IPv6 address configuration settings. The two autoconfiguration features are Stateful autoconfiguration and Stateless autoconfiguration. Stateful autoconfiguration uses the traditional DHCP services model with the DHCP server and DHCP client. There are some differences in implementation and configuration, but nevertheless, the principal functionality is still the same. Stateless autoconfiguration uses a router for IPv6 autoconfiguration. The IPv6 DHCP client sends out Router solicitation messages using the link-local all-router IPv6 multicast address FF02::2. The router responds with router advertisements that contain zero or more IPv6 prefixes used to generate global, unique-local, or deprecated site-local IPv6 addresses. In addition to the prefix information options, the router also responds with flags indicating whether Stateful autoconfiguration should still be performed by the IPv6 host. This means that an IPv6 host, by default, sends out a router solicitation, and the router responds with a router advertisement. This router advertisement may include Stateless autoconfiguration IPv6 prefixes that the IPv6 host should use in addition to telling the host through the use of flag bits whether it should also acquire additional IPv6 configuration and options through a Stateful autoconfiguration (otherwise known as DHCPv6). Figure 3 shows a Windows Vista IPv6 host that has acquired IPv6 addresses using Stateless autoconfiguration only. Figure 3. IPv6 configuration information displayed with the ipconfig.exe command-line tool. In Figure 4.10 you can see that the Wireless LAN adapter is configured with several IPv6 addresses. These are explained as follows: 2001:db8:1:1:e02b:562:3abd:7417 IPv6 address— IPv6 global address autoconfigured as the router advertised the 2001:db8:1:1::/64 prefix. fd00:1:1:0:e02b:562:3abd:7417 IPv6 address— IPv6 unique-local address that was autoconfigured as the router advertised the Fd00:1:1:0::/64 prefix. fec0:1:1:0:e02b:562:3abd:7417%1 IPv6 address— IPv6 site-local address that was autoconfigured as the router advertised the fec0:1:1:0::/64 prefix. The site-local address, as mentioned several times, is deprecated and, as also previously noted, is supported in any current IPv6 implementation. Windows Vista falls into the latter category. Temporary IPv6 addresses— These addresses are randomly generated to ensure anonymity. Because the IPv6 64-bit prefixes that are assigned to a user are the same every time a user logs on, the IPv6 address due to the use of Extended Universal Identifier (EUI)-64 format is constant. This disallows the anonymity that an IPv4 address somewhat allowed because the IPv4 DHCP address may change. Ironically, Windows Vista, by default, chooses not to use the EUI-64 format anyway because it also randomly generates those addresses when using Stateful or Stateless autoconfiguration.

Static IP Addressing Can Sometimes Be the Way to Go

On the exam, you will be asked questions that deal with deciding between assigning static IP addresses or configuring DHCP clients. Very seldom is it necessary to statically assign an IP address to Windows desktop computers nowadays. Even worse would be to statically assign all the IPv6 addresses that an IPv6 host would need. On certain occasions, though, this is necessary or, at the very least, desirable.

If a branch office network operates independent of a corporate office network or a DHCP server is not practical due to the size or location of an office, for example, static IP addressing would be acceptable. Also, another scenario would be if the wide area network (WAN) link between an office is either unreliable or the bandwidth of the link is a concern, statically assigning IP addresses on the remote IP hosts would be the better choice here too. When statically assigning the IP addresses, ensure that all IP configuration information is included in the assignment. This includes the IP address, appropriate subnet mask, default gateway address, DNS server addresses, and any WINS server addresses that may be in use if NetBIOS name resolution is still desired. It is best practice to assign the DNS and WINS server addresses that are closest to the IP host relative to WAN links when configuring the DNS and WINS server addresses for an IP host.

Remember once again, if you are statically assigning IP addresses, be sure to assign the bare minimum for IP connectivity in a routed network environment:

• IP address

• Subnet mask

• Default gateway

Netsh

Windows Vista has very powerful command-line utilities other than ipconfig.exe, and one of them is Netsh.exe. The Netsh utility can configure interfaces, Internet Protocol Security (IPSec) settings, Virtual Private Network (VPN) connections, and so forth. In addition to configuring those items, this command is also capable of displaying those same pieces of specific network configuration information. For example, if you want to display IP configuration information analogous to the ipconfig.exe command and parse out just IPv4 configuration information in the display, you enter the following information at a command line:

netsh interface ipv4 show config

Figure 4 shows the output of this command.

Figure 4. The Netsh utility displaying IPv4 configuration of a Windows Vista laptop.

In addition to displaying the previous information along with IPv4 and IPv6 routing tables and configuration information, you can script this utility to pull data from remote computers as well as configure them.