Problem: DNS records are not being updated by DHCP

The iSeries™ DHCP server is capable of dynamically updating DNS resource records. Dynamic update errors might be caused by the failure of DNS records update.

Refer to Dynamic updates for details about this capability. The DHCP server uses name resolution functions and programming interfaces to determine the appropriate dynamic DNS server to update. You can use this to your advantage when determining the source of dynamic update errors.

Check the following points when the DNS records are not being updated dynamically.

Verify which subnets and the type of resource records (A and/or PTR records) are being updated.

Check the DHCP configuration and verify that the client's subnet is set up to dynamically update resource records and which type of record is being updated.

Verify that i5/OS™ Option 31 (Domain Name System) is installed on the iSeries server that is running DHCP.

The DHCP server uses programming interfaces provided by i5/OS Option 31. The DNS that is being dynamically updated does not need to reside on the same iSeries server as the DHCP server.

Verify the DHCP server is authorized to send updates to the DNS server.

Check the DNS configuration to verify the DNS zone is configured to allow dynamic updates and that the DHCP server is included in the Access Control List.

Verify that the DNS servers can resolve the client's domain.

Display the list of DNS servers on the iSeries server where DHCP resides using the CHGTCPDMN command. Verify that these DNS servers can resolve the domain that is being updated. To do this, run NSLOOKUP from the iSeries server where DHCP is running to resolve a name (or IP address) that exists in the domain that is failing to be updated. The DHCP server must be able to derive the fully qualified domain name (FQDN) of the client to update its DNS record. The DHCP server will not attempt to update a dynamic DNS without a FQDN (the host name and domain name of the client). The DHCP server derives the FQDN of the client using the following sequence:

1. Option 81 (Client FQDN) in the DHCPREQUEST message from the client.
2. Option 12 (Host Name) and/or Option 15 (Domain Name) in the DHCPREQUEST message from the client.
3. Option 12 (Host Name) in the DHCPREQUEST message from the client and/or Option 15 (Domain Name) configured in the DHCP server. In this case, to derive the FQDN, the DHCP server must be configured to append the domain name to the host name (specified on the Properties > Dynamic DNS tab for the global level, subnet, class, or client).

The TXT record might not match the corresponding DNS record.

The DHCP server can be configured to check the existing DNS resource records to determine which DHCP client they are associated with. The DHCP server accomplishes this by writing a corresponding TXT record with each A and PTR record that it updates in the DNS. If the server is configured to verify the client ID before performing the DNS update, then the TXT record data must match the client ID of the client that received the address from the DHCP server. If it does not match, the DHCP server will not update the DNS A resource record. This is done to prevent overwriting existing records. However, the DHCP server can be configured to ignore the existing records and perform DNS updates regardless of the data in the TXT record (specified on the Properties > Dynamic DNS tab for the global level, subnet, class, or client).