There is a difference in how the DNS server treats static and dynamic records. Once registered in the DNS server, information in static records are always considered valid. However, this does not apply to dynamic records. Dynamic records need to be renewed periodically to retain its validity status in the DNS server. This renewal process of a dynamic record can be through refresh or update. In this article, weâ€™re going to cover what are those process actually does and help you Understanding the Concept of Refresh and Update in Windows DNS Server.
Understanding the Concept of Refresh and Update in Windows DNS Server
Understanding the concept of refresh and update in Windows DNS server is the key to maintaining dynamic records. Before we get to there, take a look at the figure below for a quick reminder of what makes the difference between static and dynamic record:
Yes, the difference between a static and dynamic record is the timestamp. Static record does not have timestamp, but dynamic record does. Timestamp is the indicator of when the last time a renewal process happens to a specific record. Now the question here is who is performing the record renewal process?
The answer is the owner of the record that performs renewal process. By default, record owner is the same the machine that uses the name and IP address combination in the record. This behavior applies to all the latest Windows version (such as Windows 7/8/10, Windows Server 2008/2012, and above) with a static IP address. Windows machine with static IP address will register their own A and PTR record to the DNS server. It is then the machine itself who will perform renewal for its own records.
In a case where Windows machine obtaining IP address from a DHCP server, it is the DHCP server that registers the A and PTR record to DNS server on behalf of the DHCP client. But the owner of the record by default is still the Windows machine (DHCP client) itself, unless the DHCP server is configured to take ownership of the record.
Refresh vs Update
Now that we know who is performing the renewal of a record, we can dive deeper into the renewal process itself. We mention on the opening paragraph that renewal of a DNS record can be through a refresh or update. So, what is the difference between refresh and update?
Refresh means renewing the timestamp of a record in DNS server, if the record owner still connected to the network while using the same hostname and IP address combination. A Windows machine will by default refresh the timestamp for its own record in the DNS server every 24 hours.
Now if refresh happens when there is no change on the information of a record, update happens when there is a change on the record. For example, in a case where the record owner changes its IP address, or getting different IP address from the DHCP server. When update happens, timestamp renewal also occurs along with the information change.
Even though the owner is no longer doing refresh/update, their record may still exist on the DNS server. But after some period of time without refresh/update, that record will turn into a stale record. Usually this happens if the owner disconnect from the network for some time or the owner is using different name.
The Importance of DNS Record Refresh and Update
After understanding the concept of refresh and update in Windows DNS server, you should know why they are so important. Both refresh and update happen on dynamic records, which means the information on these records are not going to valid forever. Refresh and update process are there to ensure the dynamic records remain current. If refresh/update no longer happens to a record, then it may age and turns into stale record. Along with scavenging, these are the process that an administrator should understand to effectively manage Windows DNS server.