System Administration Guide: IP Services

How to Enable Dynamic DNS Updating for DHCP Clients

Note –

Be aware that dynamic DNS updates are by nature a security risk.

By default, the Solaris DNS daemon (in.named) does not allow dynamic updates. Authorization for dynamic DNS updates is granted if the requesting host's IP address is assigned to the allow-update keyword in the appropriate zones of the named.conf configuration file on the DNS server system. No other security is provided. You must carefully weigh the convenience of this facility for users against the security risk created when you enable dynamic DNS updates.

  1. At the DNS server, edit the /etc/named.conf file as root.

  2. Find the zone section for the appropriate domain and add the DHCP server's IP addresses to the allow-update keyword.

    For example, if the DHCP server resides at addresses and, a named.conf file for the zone would be modified as follows:

    zone "" in {
                 type master;
                 file "db.dhcp";
                 allow-update {;; }; 
    zone "10.IN-ADDR.ARPA" in {
                 type master;
                 file "db.10"; 
                 allow-update {;; };

    Note that allow-update for both zones must be enabled to allow the DHCP server to update both A and PTR records on the DNS server.

  3. On the DHCP server, start DHCP Manager.

  4. Choose Modify from the Service menu.

    The Modify Service Options dialog box opens.

  5. Select Update DNS Host Information Upon Client Request.

  6. Specify the number of seconds to wait for a response from the DNS server before timing out, then click OK.

    The default value should be adequate. If you have timeout problems, you can increase the value later.

  7. Click the Macros tab and ensure that the correct DNS domain is specified.

    The DNSdmain option must be passed with the correct domain name to any client that expects dynamic DNS update support. By default, DNSdmain is specified in the server macro, which is used as the configuration macro bound to each IP address.

  8. Set up the DHCP client to specify its host name when requesting DHCP service.

    If you use the Solaris DHCP client, see How to Enable a Solaris Client to Request Specific Host Name. If your client is not a Solaris DHCP client, see the documentation for your DHCP client for information about how to do this.