Using dynamic DNS to update host information

About dynamic DNS updates

Dynamic DNS updates enable your storage system to send new or changed DNS information to the primary master DNS server for your storage system's zone.

Need for dynamic DNS updates

Without dynamic DNS updates, system administrators have to manually add DNS information (DNS name and IP address) to the identified DNS servers when a new system is brought online or when existing DNS information changes. This process is not only slow, but also error-prone.

Additionally, in a disaster-recovery situation when a storage system with a large number of vFiler units is brought online, manual configuration of DNS information for those vFiler units can result in a longer-than-needed downtime.

By enabling dynamic DNS updates on your storage system, you allow your storage system to automatically send information to the DNS servers as soon as the information changes on the system.

For example, if you want to change the IP address on interface e0 of StorageSystem1, you can simply configure e0 with the new IP address. StorageSystem1 automatically sends updated information to primary master DNS server for StorageSystem1.

How dynamic DNS updates work in Data ONTAP

If dynamic DNS updates are enabled on your storage system, it periodically sends updates to the primary master DNS server for its zone. Your storage system finds out the primary master DNS server for its zone by querying the DNS servers configured in storage system's /etc/resolv.conf file. The primary master DNS server might be different from the ones configured in your storage system's /etc/resolv.conf file.

By default, periodic updates are sent every 12 hours. A time-to-live (TTL) value is assigned to every DNS update sent from your storage system. The TTL value defines the time for which a DNS entry is valid on the DNS server. By default, the TTL value is set to 24 hours, and you can change it.

In addition to periodic updates, DNS updates are also sent if any DNS information changes on your storage system.

When your storage system sends an update to the DNS server, it waits up to five minutes to receive an acknowledgement of the update from the server. If it does not receive an acknowledgement, the storage system sends the update again. This time, the storage system doubles the waiting interval (to 10 minutes), before sending the update. The storage system continues to double the waiting interval with each retry until a waiting interval of 160 minutes or TTL/2, whichever is less, is reached.

Support for dynamic DNS updates in Data ONTAP

When using dynamic DNS updates in Data ONTAP, the following conditions apply:

By default, dynamic DNS updates are disabled in Data ONTAP.
Dynamic DNS updates are supported on UNIX and Windows systems.
On Windows DNS servers, secure dynamic DNS updates can be used to prevent malicious updates on the DNS servers. Kerberos is used to authenticate updates.
Even if secure dynamic DNS updates are enabled, your storage system initially tries sending updates in clear text. If the DNS server is configured to accept only secure updates, the updates sent in clear text are rejected. Upon rejection, the storage system sends secure DNS updates.
For secure dynamic DNS updates, your storage system must have CIFS running and must be using Windows Domain authentication.
Dynamic DNS updates can be sent for the following:
- Vif and VLAN interfaces
- vFiler units
You cannot set TTL values for individual vFiler units. All vFiler units inherit the TTL value set for vFiler0, which is the default vFiler unit and is the same as the physical storage system.
DHCP addresses cannot be dynamically updated.
In a takeover situation, the hosting storage system is responsible for sending DNS updates for IP addresses for which it is responding.

Enabling dynamic DNS updates

To enable your storage system to send dynamic DNS updates automatically, complete the following step on your storage system.

Step	Action
1	Enter the following command: options dns.update.enable [ off \| on \| secure ] `Off`--Disable dynamic DNS updates `On`--Enable dynamic DNS updates `Secure`--Enable secure dynamic DNS updates Note Secure dynamic DNS updates are supported for Windows DNS servers only.

Changing the time-to-live setting for DNS entries

To change the TTL for the DNS entries, complete the following step.

Step	Action
1	Enter the following command: options dns.update.ttl time where time can be set in seconds (`s`), minutes (`m`), or hours (`h`) with a minimum value of 600 seconds and a maximum value of 24 hours. For example, to set the TTL to two hours, enter the following command: options dns.update.ttl 2h

Step

Action

Enter the following command:

options dns.update.ttl time

where time can be set in seconds (s), minutes (m), or hours (h) with a minimum value of 600 seconds and a maximum value of 24 hours.

For example, to set the TTL to two hours, enter the following command:

options dns.update.ttl 2h