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This chapter explains how to use dynamic DNS update with Network Registrar servers using both the GUI and the CLI. You can configure dynamic DNS update after you configure your DHCP servers.
This is the process you follow to configure dynamic DNS update:
Step 1 Configure the DHCP scope to do dynamic DNS updates.
Step 2 Configure the DNS zones to accept dynamic DNS updates.
Step 3 Define advanced dynamic DNS update support. You rarely need to modify the system defaults for the advanced parameters; however they are described in "Defining Advanced Dynamic DNS Update Support" section for your reference.
Step 4 Reload the servers you have configured.
The remainder of this chapter describes each step in more detail. lists the dynamic DNS update configuration topics explained in this chapter and their associated sections.
| If you want to... | Go to this section... |
|---|---|
Know more about why you would configure dynamic DNS update | |
Know more about how the DHCP Event Service works when dynamic DNS update is configured | |
Configure dynamic DNS update for the scope | |
Enable dynamic DNS updates from host names | |
Reload the servers after you have configured dynamic DNS update | |
Further define dynamic DNS update support by changing system defaults for advanced parameters |
Administrators of standard DNS have to update multiple configuration files and restart the DNS server or servers to change the association between a name and an address. This restricts the usefulness of DHCP, because an individual client's address may not be the same for more than a day (or even a few hours). While there is no requirement that DNS names exist for every host, there are some Internet services that will not operate correctly unless the hosts appear in DNS. One solution is to place unique names in DNS for all of the addresses allocatable by DHCP, for example DHCP25.example.com. While this method works, you may need to have more descriptive names in DNS for your clients.
Network Registrar's dynamic DNS update allows the DHCP server to tell the DNS server or servers when a name-to-address association has been created or changed. When a host obtains a lease for an address, Network Registrar tells DNS to add it to its database. When the lease expires, or when the client gives up an address, Network Registrar tells DNS to remove the association. In normal operation you, as administrator, do not have to reconfigure DNS, no matter how frequently the clients' addresses change through the use of DHCP. Network Registrar uses the host name that the client computer provides. If you choose, Network Registrar can automatically create names for clients who have not provided one.
The Network Registrar dynamic DNS update is used for individual hosts instead of the DNS servers themselves. DNS servers' addresses are entered into the DHCP client information database and should therefore only be changed infrequently. DNS servers' addresses are often known to one another for backup or performance reasons. We do not recommend that you change their addresses in a mixed environment. For security, the DHCP servers must know the addresses of the DNS servers that they update, and the DNS servers must know the addresses of the DHCP servers from which they are authorized to accept updates.
Dynamic DNS resource records do not appear in the DNS GUI interface. If you want to confirm that the DNS update is working, type:
nrcmd> zone testzone listRR dynamic
A complete list of dynamic updates appears.
The Network Registrar DHCP server stores all pending DNS update information on disk. If DHCP cannot communicate with a particular DNS server, it periodically tests if communications have been re-established, and submits all pending updates when they have been updated. This test typically occurs once every 40 seconds until communication with DNS is re-established.
Step 1 From the Server Manager window (Figure 2-3), select the DHCP scope you want to associate with dynamic DNS update.
Step 2 Click the Show Properties toolbar button.
Step 3 In the DNS tab of the DHCP Scope Properties dialog box (Figure 8-1), select the Perform dynamic DNS updates check box.
Step 4 Enter the forward DNS zone name.
This is the name of the DNS zone to which a DHCP client's host name should be added (A record).
Step 5 Enter the forward DNS Server's IP address.
This is the IP address of the primary DNS server on which the forward zone resides.
Step 6 Enter the reverse DNS zone name.
This is the name of the inverse (in.addr.arpa) zone that is updated with the PTR and TXT records.
Step 7 Enter the Reverse DNS Server's IP address.
Step 8 Select whether to update DNS before or after providing a lease.
The default is "After responding to client." Do not choose "Before responding to client" if you have Windows 95 clients, because updating DNS before responding to a lease can cause delays which then cause problems with Windows 95 DHCP clients.
Step 9 If you want Network Registrar to create host names for hosts that do not supply names, select the Create host names for hosts that do not supply one check box.
If you select this check box, Network Registrar will create a unique host name by prepending the word "dhcp" to the server's ID within the cluster followed by a number, such as dhcp-1-1...dhcp-1-n.
Step 10 If you want Network Registrar to use a specific host name prefix, enter the prefix.
Step 11 Click OK.
You can use the scope set and enable commands to enable Dynamic DNS for the scope.
Step 1 Use the scope set command to set the values for the zone name.
This is the name of the zone to which a DHCP client's host name should be added. For example, if you want your DNS name to be beth.QuickExample.com, specify the zone QuickExample.com.
nrcmd> scope testScope set dns-zone-name=QuickExample.com
Step 2 Use the scope set command to set DNS server's IP address.
You should specify the IP address of the primary server on which both the forward and reverse zones reside. Both zones must be primary servers, and must be on a server that supports the DDNS protocol.
nrcmd> scope testScope set dns-server-addr=192.168.1.1
Step 3 Use the scope set command to set DNS reverse zone's name.
This is the name of the zone to be updated with PTR and TXT records.
nrcmd> scope testScope set
dns-reverse-zone-name=1.168.192.in-addr.arpa
Step 4 Use the scope set command to set DNS reverse zone's IP address.
nrcmd> scope testScope set
dns-rev-server-addr=192.168.1.14
Step 5 Use the scope enable command to enable dynamic updates for this scope.
nrcmd> scope testScope enable dynamic-dns
Step 6 Use the server command to reload the server.
nrcmd> server DHCP reload
Step 1 From the Server Manager window (Figure 2-3), select the DNS zone that you want to configure for dynamic DNS updates.
Step 2 Click the Show Properties toolbar button.
Step 3 From the DNS Zone Properties dialog box, click the DHCP tab (Figure 5-7).
Step 4 Select the Enable dynamic DHCP updates check box.
Step 5 Specify the address of the DHCP server from which DNS allows updates.
If you do not list a DHCP server, dynamic updates will not occur.
Step 6 Repeat steps 1 through 5 for both the primary and reverse DNS zones.
For example, the primary zone example.com and the reverse zone 1.168.192.in-addr.arpa.
Step 1 Use the zone enable command to enable dynamic DNS updates from host names.
nrcmd> zone example.com enable dynamic
Step 2 Use the zone set command to specify the name of the server.
nrcmd> zone example.com set dynupdate-set=192.168.1.10
Repeat this procedure for both the primary and reverse DNS zones; for example, the primary zone example.com and the reverse zone 1.168.192.in-addr.arpa.
Step 1 From the Server Manager window (Figure 2-3), select the first server you want to reload, for example the DNS server.
Step 2 Click the Control toolbar button.
Step 3 From the Control dialog box, click Reload.
Step 4 Click OK.
Step 5 Repeat steps 1 through 4 for the second server; for example, the DHCP server.
Use the server command to reload the server.
nrcmd> server DNS reload
Repeat for the DHCP server.
If you plan to use dynamic DNS update, you must configure both the DHCP and DNS servers. For more information about how dynamic DNS update works with Network Registrar servers, see the "About Dynamic DNS Update" section.
Defining advance dynamic DNS update suppot involves setting these parameters:
The default is 500.
Step 1 From the Server Manager window (Figure 2-10), select the DHCP server for which you want to configure advanced dynamic DNS update options.
Step 2 Click the Show Properties toolbar button.
Step 3 Click the Advanced DNS tab of the DHCP Scope Properties dialog box (Figure 8-2).
Step 4 Set the number of DNS packets in the Number of DNS packets field.
Step 5 Do not set this any lower than the number of DHCP responses in the Advanced tab of the DHCP Server Properties dialog box. For more information, see the "Defining Advanced Parameters" section.
Do not set this any lower than the number of DHCP responses (max-dhcp-responses).
Use the dhcp command to set the max-dns-packets property.
nrcmd> dhcp set max-dns-packets=400
Do not change this value unless instructed by Technical Support.
The default is 512 bytes.
Step 1 From the Server Manager window (Figure 2-10), select the DHCP server for which you want to configure advanced dynamic DNS update options.
Step 2 Click the Show Properties toolbar button.
Step 3 Click the Advanced DNS tab of the DHCP Scope Properties dialog box (Figure 8-2).
Step 4 Enter the value in bytes in the DNS packet size field.
Step 5 Click OK.
The default is 3.
Step 1 From the Server Manager window (Figure 2-10), select the DHCP server for which you want to configure advanced dynamic DNS update options.
Step 2 Click the Show Properties toolbar button.
Step 3 Click the Advanced DNS tab of the DHCP Scope Properties dialog box (Figure 8-2).
Step 4 Enter a value in the Number of DNS retries field.
Step 5 Click OK.
Use the dhcpcommand to set the max-dns-retries property.
nrcmd> dhcp set max-dns-retries=6
You can control the number of times the DHCP server can try to add a host into DNS even if it detects that the host's name is already present in DNS. This value controls the number of times the DHCP server will attempt to modify a host's name to resolve a conflict.
The default is 3.
Step 1 From the Server Manager window (Figure 2-10), select the DHCP server for which you want to configure advanced dynamic DNS update options.
Step 2 Click the Show Properties toolbar button.
Step 3 Click the Advanced DNS tab of the DHCP Scope Properties dialog box (Figure 8-2).
Step 4 Enter a value in the Number of DNS remaining retries field.
Step 5 Click OK.
Use the dhcp command to set the max-dns-renaming-retries property.
nrcmd> dhcp set max-dns-renaming-retries=6
The default is 5000 milliseconds.
Step 1 From the Server Manager window (Figure 2-10), select the DHCP server for which you want to configure advanced dynamic DNS update options.
Step 2 Click the Show Properties toolbar button.
Step 3 Click the Advanced DNS tab of the DHCP Scope Properties dialog box (Figure 8-2).
Step 4 Enter a value in milliseconds in the DNS request timeout field.
Step 5 Click OK.
Use the dhcp command to set the dns-timeout property.
nrcmd> dhcp set dns-timeout=3600
You can set the TTL ceiling, in seconds, for DNS records added through dynamic DNS. When the DHCP server adds a DNS record, it sets the TTL to the smaller of one-third of the lease time, or this ceiling value. The DNS record's effective TTL may be determined by the DNS zone's minimum TTL. For more information, see the "Setting Maximum Cache TTL" section.
The default is 86400 seconds.
Step 1 From the Server Manager window (Figure 2-10), select the DHCP server for which you want to configure advanced dynamic DNS update options.
Step 2 Click the Show Properties toolbar button.
Step 3 Click the Advanced DNS tab of the DHCP Scope Properties dialog box (Figure 8-2).
Step 4 Enter a value in seconds in the Maximum DNS record time to live field.
Step 5 Click OK.
Use the dhcp command to set the max-dns-ttl property.
nrcmd> dhcp set max-dns-ttl=3600
Posted: Thu Nov 18 13:41:49 PST 1999
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