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Windows Server 2003 : Configuring DNS Clients (part 2)

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3/9/2011 5:39:16 PM

Configuring Dynamic Update Options

When configured to do so, DNS servers running on Windows 2000 or Windows Server 2003 can accept dynamic updates of A and PTR resource records. The updates themselves must be performed either by a DNS client running Windows 2000, Windows XP, or Windows Server 2003, or by a DHCP server (on behalf of a DNS client) running Windows 2000 or Windows Server 2003.

Tip

For the exam, remember that UNIX-based DNS servers running Berkeley Internet Name Domain (BIND) 8.1.2 or later can accept dynamic updates.


Dynamic updates can occur only when clients are configured with a domain suffix that matches the zone name hosted by the preferred DNS server. In other words, for the record of a computer named Client1 to be dynamically updated in the lucernepublishing. com zone, the FQDN of that computer must be client1.lucernepublishing.com., and the client must specify as its DNS server the IP address of the DNS server hosting lucernepublishing.com.

Default Client Update Behavior

By default, DNS clients that are configured with a static IP address and an appropriate domain suffix attempt to register and update both A and PTR resource records with the preferred DNS server. However, DNS clients that obtain their address from a DHCP server attempt to register and update only their A resource records with the preferred DNS server. In this case, the PTR resource record is updated by the DHCP server when the lease is assigned. Windows clients that are not capable of performing dynamic updates—such as DNS clients running Windows Me or Windows NT 4—can have both A and PTR resource records updated on their behalf by a specially configured DHCP server.

To configure a DNS client to attempt dynamic updates in DNS, make sure the Register This Connection’s Addresses In DNS check box is selected on the DNS tab of the Advanced TCP/IP Settings dialog box, as shown in Figure 4-15. (It is selected by default.) This configures the DNS client to attempt to register and update the computer’s full computer name (primary domain name). When you clear this check box, the DNS client no longer attempts dynamic updates. If you configure a DNS suffix for the connection, you can also specify that the DNS client attempt to dynamically register and update an FQDN based on this connection-specific suffix. To do so, click the Use This Connection’s DNS Suffix In DNS Registration check box. (It is not selected by default.)

To force a DNS client to attempt dynamic registration of its A and PTR resource records, type ipconfig /registerdns at a command prompt.

Note

For Internet Connection Sharing (ICS) clients, Dynamic DNS updates are configured in a distinct manner. When DNS clients running Windows 2000, Windows XP, or Windows Server 2003 obtain their IP configuration from a computer running ICS, those clients can update their records in DNS only when the Use This Connection’s DNS Suffix In DNS Registration is selected. You do not need to specify a connection-specific suffix. Instead, the primary DNS suffix forms the FQDN.


Configuring TCP/IP Settings for DNS Clients

The following procedure summarizes the steps necessary to enable clients to use DNS.

To configure TCP/IP settings for DNS clients, complete the following steps:

1.
Open the Network Connections window.

2.
Right-click the network connection you want to configure, and then select Properties.

The connection’s properties dialog box appears.

3.
On the General tab (for a local area connection) or the Networking tab (all other connections), select the Internet Protocol (TCP/IP) component, and then click Properties.

The Internet Protocol (IP) Properties dialog box appears.

4.
If you want to obtain DNS server addresses from a DHCP server, select Obtain DNS Server Address Automatically.

5.
If you want to manually configure DNS server addresses, select Use The Following DNS Server Addresses, and in the Preferred DNS Server text box and Alternate DNS Server text box, type the preferred DNS server and alternate DNS server IP addresses.

6.
To configure advanced DNS properties, click Advanced, select the DNS tab, and do one or more of the following:

  1. To configure an additional DNS server IP address, click the topmost Add button and specify a DNS server IP address.

  2. To modify the resolution behavior for unqualified DNS names, do the following:

    • To configure the client to resolve an unqualified name by adding the primary DNS suffix and the DNS suffix of each connection (if configured), select Append Primary And Connection Specific DNS Suffixes. If you also want to search the parent suffixes of the primary DNS suffix up to the second-level domain, select the Append Parent Suffixes Of The Primary DNS Suffix check box.

    • To configure the client to resolve an unqualified name by adding the suffixes from a list of configured suffixes, select Append These DNS Suffixes, and then click Add to add suffixes to the list.

  3. To configure a connection-specific DNS suffix, type the DNS suffix in the DNS Suffix For This Connection text box.

  4. To modify DNS dynamic update behavior, do the following:

  • configure the client to register the connection’s IP address with the local computer’s full computer name in DNS, select the Register This Connection’s Addresses In DNS check box. This option is enabled by default. This option requires that the primary DNS suffix of the computer match a domain hosted by the preferred DNS server.

  • configure the client to register the connection’s IP address with a connection-specific FQDN, select the Use This Connection’s DNS Suffix In DNS Registration check box. This option is disabled by default.

  • completely disable DNS dynamic updates for all names on the computer, clear the Register This Connection’s Addresses In DNS check box for all connections in Network Connections.

Viewing and Clearing the DNS Resolver Cache

The DNS resolver cache, also known as the DNS client cache, is maintained separately from the DNS server cache. This resolver cache is checked first by DNS clients before they attempt to query a DNS server. New entries are added to the resolver cache whenever a DNS client receives a query response from a DNS server.

To view the DNS client cache, enter ipconfig /displaydns at a command prompt. The output of this command includes entries loaded from the local Hosts file, as well as any recently obtained resource records for name queries resolved by the system.

To clear the DNS resolver cache, you can enter ipconfig /flushdns at the command prompt. Alternatively, you can restart the DNS Client service by using the Services console, an administrative tool accessible through the Start menu.

Tip

Remember the following DNS-related commands for the exam:

  1. Ipconfig /displaydns. Displays the contents of the DNS client cache

  2. Ipconfig /flushdns. Purges the contents of the DNS client cache

  3. Ipconfig /registerdns. Refreshes all DHCP leases and reregisters DNS names with DNS zones configured to accept dynamic updates

Know also that the Ipconfig / registerdns command can be used only on clients running Windows 2000, Windows XP, and Windows Server 2003.


Tip

For the exam, remember that you sometimes need to run Ipconfig /flushdns on your computer before you can see the benefit of having fixed a DNS problem elsewhere on the network. For example, suppose you are unable to ping a UNIX computer by name from a Windows client. You manually create a host (A) resource record for the UNIX computer to remedy the situation, but when you again try to ping the UNIX computer by name, you still receive an error response. This problem occurs because the Windows client has cached a negative response to the earlier query for the UNIX computer name. To fix the problem, flush the DNS client cache by executing Ipconfig /flushdns on the Windows computer. This command forces the Windows client to attempt from scratch to resolve the UNIX computer name instead of just responding with the cached negative response.


Practice 1: Configuring a Primary DNS Suffix

In this practice, you configure a primary DNS suffix for Computer1 and Computer2 and then observe changes resulting from this procedure in the DNS console.

Exercise 1: Adding Suffix Names to Computers

In this exercise, you configure a primary DNS suffix for Computer1 and Computer2.

  1. Log on to Computer1 as Administrator.

  2. In Control Panel, open the System tool.

    The System Properties dialog box opens.

  3. Click the Computer Name tab.

  4. Click the Change button.

    The Computer Name Changes dialog box opens.

  5. Click More.

    The DNS Suffix And NetBIOS Computer Name dialog box opens.

  6. In the Primary DNS Suffix Of This Computer text box, type domain1.local.

  7. Click OK.

  8. In the Computer Name Changes dialog box, click OK.

    The Computer Name Changes message box appears, indicating that you need to restart the computer for the changes to take effect.

  9. Click OK.

  10. In the System Properties dialog box, click OK.

    The System Settings Change dialog box opens, which asks you whether you want to restart your computer now.

  11. Click Yes.

  12. While Computer1 is restarting, perform this same procedure on Computer2, assigning the primary DNS suffix of domain1.local, and then choosing to restart the computer.

Practice 2: Configuring a DNS Server to Perform Recursion

In this practice, you configure the DNS server on Computer1 to answer recursive queries for Internet-based DNS names from Computer2. You then initiate a recursive query from Computer2 and monitor the results.

Because Computer2 is assigned a private address, it can communicate with the Internet only by means of an address translation service such as Network Address Translation (NAT) or ICS. As a result, the first step in this practice is to configure ICS on Computer1.

Exercise 1: Enabling ICS

In this exercise, you enable ICS on Computer1. This feature performs address translation for all computers on the network segment and enables them to communicate with Internet hosts. ICS also provides addresses for DHCP clients on the local segment and configures these clients to use the ICS computer as a DNS server. After ICS is enabled, the DNS server on the ICS server performs recursion to answer the DNS queries from local clients.

  1. Log on to Computer1 as Administrator.

  2. Open the Network Connections window.

  3. If the MyISP connection is active in the Network Connections window, right-click MyISP and select Disconnect.

  4. After the dial-up connection has finished disconnecting, right-click MyISP and select Properties.

    The MyISP Properties dialog box opens.

  5. Click the Advanced tab.

  6. In the Internet Connection Sharing area, select the Allow Other Network Users To Connect Through This Computer’s Internet Connection check box.

  7. Click OK.

    The Network Connections dialog box opens.

  8. Read the text in the box, and then click Yes.

    At this point, the local computer is assigned an IP address of 192.168.0.1. You might temporarily lose network connectivity while these changes are being made.

  9. Log on to Computer2 as Administrator.

  10. Restart Computer2.

Exercise 2: Performing Recursive Queries

In this exercise, you use Network Monitor to capture a DNS query from Computer2. After Computer1 performs recursion to answer the query, you explore the capture and verify that new entries corresponding to the query have been loaded into the DNS Server cache.

  1. Connect Computer1 to the Internet through the MyISP connection.

  2. Log on to Computer2 as Administrator and open a command prompt.

  3. At the command prompt, type ipconfig /all, and then press Enter.

    Because ICS has been enabled on the network, Computer2 now specifies 192.168.0.1, the address of Computer1, as its DNS server. Computer2 therefore resolves DNS queries through Computer1.

  4. At the command prompt, type ipconfig /flushdns, and then press Enter.

    The resolver cache clears, which forces Computer2 to contact a DNS server to resolve all DNS names.

  5. Switch to Computer1, open Network Monitor, and begin a Network Monitor capture.

  6. Switch back to Computer2, and then open Internet Explorer. If you receive a message box informing you that an enhanced security configuration is currently enabled, select the check box to prevent this message from appearing again, and then click OK.

  7. In the Address text box in Internet Explorer, type http://www.windowsupdate.com, and then press Enter.

    The connection is successful.

  8. Switch back to Computer1 and in Network Monitor, click the Stop And View Capture button.

  9. In the Capture: 1 (Summary) window, locate and double-click the first DNS frame in the capture. Note that the FQDN queried for in the first line is www.windows-update.com.

  10. Within the expanded DNS frame in the details (center) pane, expand the section named DNS Flags.

    A set of flagged messages appear. These messages are true when the corresponding flag is set to 1.

  11. Answer the following question: Which of the DNS flags is set to 1 and not 0?

    Recursive Query Desired

    This flag serves as a request that the DNS server perform recursion to answer the query if necessary.

  12. Close Network Monitor. Do not save the capture or choose to save any entries to the database.

  13. Open the DNS console. (If the DNS console is already open, close the console and reopen it.)

  14. In the console tree, select the COMPUTER1 icon.

  15. From the View menu, select Advanced.

    A new folder named Cached Lookups appears in the console tree.

  16. Expand the Cached Lookups folder, and then expand the .(root) folder.

    Within the .(root) folder, browse the subfolders to locate the CNAME record www.windowsupdate.com.

    Computer1 has performed recursion to answer Computer2’s recursive query. The DNS Server service has then cached the records returned in the response to the query.

  17. Log off Computer1 and Computer2.

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