Like other DNS implementations, the Windows Server 2003 implementation of DNS supports load balancing through the use of round robin and netmask ordering. Load balancing distributes the network load between multiple network cards if they are available. You can create multiple resource records with the same hostname but different IP addresses for multihomed computers. Depending on the options that you select, the DNS server will respond with the addresses of one of the multihomed computers.
If round robin is enabled, the first address that was entered in the database is returned to the resolver and then sent to the end of the list. The next time a client attempts to resolve the name, the DNS server will return the second name in the database (which is now the first name) and then send it to the end of the list and so on.
If netmask ordering is enabled, the DNS server will use the first IP address in the database that matches the subnet of the resolver. If none of the IP addresses match the subnet of the resolver, then the DNS server reverts to round robin. If round robin is disabled, the DNS server simply returns the first IP address in the database.
If neither round robin nor netmask ordering is enabled, the DNS server always returns the first IP address in the database. This usually isn't very helpful, so fortunately round robin and netmask ordering are both enabled by default. You will see how to enable and disable round robin and netmask ordering in the section titled "Configuring Advanced Properties."
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