DNS Client Behavior in Windows Vista and Server 2008

Microsoft developers have changed the functionality of many of Windows’ components. DNS is one of them. A DNS client component running on a Vista computer behaves differently than it did in previous versions of Windows.

Win Tip: DNS functions differently in the latest versions of Windows. For a quick explanation of DNS client behavior for DNS queries and registrations look no further.

This tip explains the behavior of the DNS client component in Windows Vista for DNS queries and registrations.

Windows Vista will need to perform two types of DNS queries: A and AAAA. The A is for IPV4 and AAAA is for IPV6. It could be that one of the endpoints or IP Addresses the DNS Server supplied is not reachable and the client retries at DNS server. This will put the load on the DNS server when multiple clients send DNS queries.

The following changes have been made to the DNS client component to minimize the impact on the DNS server:

1. If the client computer has only link-local or Teredo IPV6 addresses assigned, then the DNS Client will send only a single query for its A records.
2. If the client computer has at least one IPV6 address, and this is not the Teredo address, the DNS client service sends DNS query for A records and a separate query for AAAA records. If the A record query times out or returns with a negative response, the corresponding AAAA query is not re-sent.
3. Windows Vista Client computers will always use IPV6 over IPV4 (e.g., AAAA Over A queries).

DNS Registration Behavior in Windows Vista and Windows Server 2008

The DNS Client Service in both operating systems uses DNS Dynamic update and registers the following records:

1. A records for all IPV4 addresses assigned to the interfaces configured with a DNS Server address.
2. PTR records for IPV4 addresses assigned to the interfaces.
3. AAAA records for all IPV6 addresses assigned to the interfaces configured with the DNS Server address.