There are three types of DNS server operation modes. These modes are not something we can choose during the setup process. They are listed based on their characteristics:
- Dynamic: AD DS-directory-integrated DNS uses DynDNS by default. DynDNS allows hosts and users to register, update, and remove DNS records from DNS servers. Let's assume we have an AD environment with 200 computers. It uses Dynamic Host Configuration Protocol (DHCP) to maintain the IP assignment; so every three days, each device will renew its IP allocation. Some may have the same IP address, but some may receive a new one. But if the system uses static DNS every three days, administrators will need to update the DNS list to match IP allocations. Also, AD will not be able to find the devices to establish authentication or handle resource access requests. However, thanks to DynDNS, this is no longer manual work, and it allows the environment to maintain up-to-date DNS information without user interaction.
- Read/write: This is applicable when DNS zones run without AD DS integration. For example, one of the Rebeladmin Corp. clients wants to host their own web server. Therefore, as a service provider, we need to provide a solution, which DNS design is part of. The client likes to keep the cost to a minimum, and since it's a testing environment, they aren't worried about high availability. For their web server DNS requirements, we can set up a standalone DNS server in the same web server and use it as an authoritative DNS server. Records there are not going to change often, so there is no need for DynDNS. If records need to be updated, an authorized user can update them manually.
- Read-only: If the DNS server only keeps a read-only copy of a master zone, it operates in read-only mode. Some DNS servers keep only secondary zones for security, load balancing, or disaster recovery purposes. This can typically be seen in web-server farms. Read-only DNS servers will check with master DNS servers for DNS updates periodically.
With Windows Server 2008, Microsoft introduced read-only domain controllers (RODCs). RODCs can be used in infrastructures where physical security and connectivity cannot be guaranteed. RODCs run AD DS-integrated primary DNS zones in read-only mode.
These operation modes can be used in infrastructures in order to meet their DNS requirements. It is possible to mix DNS servers with different operation modes. But it's important to clearly understand the capability of each operation mode for DNS troubleshooting.