New Features in Windows Server 2003
Windows Server 2003 includes the following new DNS features that are not in Windows 2000:
Application naming contexts.
If you use Active Directory Integrated zones, you can configure DNS to store the resource records in separate Active Directory naming contexts rather than putting them all in the Domain naming context. This simplifies zone replication in a large forest. An executable called Dnsadddp.exe runs each time a domain controller is booted. This application is responsible for creating the DNS application partitions if they do not already exist. See Chapter 7, "Managing Active Directory Replication," for more information on DNS naming contexts and replication.
DNS stub zones.
This feature simplifies zone delegation. A stub zone contains the Start of Authority (SOA) and Name Server (NS) records associated with a child zone along with the A records for the name servers. The stub zone then periodically checks the child zone and pulls updates if the NS records have changed. This eliminates the need to manually update delegation records.
This feature permits a name server to select a forwarder based on the domain specified in a client query rather than forwarding all out-of-zone queries to a single DNS server.
IPv6 host records.
An IPv6 host address uses a 128-bit address space in contrast to the 32-bit address space used in IPv4. Windows Server 2003 DNS supports the AAAA host resource record that contains IPv6 addresses. This feature is based on RFC 1886, "DNS Extensions to Support IP Version 6." Windows Server 2003 does not include support for the newly proposed A6 resource record type and the proposed restructuring of the IPv6 reverse lookup zone outlined in RFC 2874, "DNS Extensions to Support IPv6 Address Aggregation and Renumbering."
The current DNS implementation uses UDP for exchanging information between name servers and clients. The standard UDP datagram is limited to 512 octets. Many new and proposed DNS features require more than 512 octets. Currently, this requires a setup and teardown of a TCP session when delivering large resource records, adding overhead and complexity. Windows Server 2003 permits a client and name server to negotiate a larger datagram size, if possible. This feature is based on RFC 2671, "Extension Mechanisms for DNS (EDNS0)."
Reverse lookup zone subnetting.
In Windows Server 2003, if you use non-standard subnet masking, you can specify the subnet mask as part of the reverse lookup zone name. This enables the system to apportion Pointer (PTR) records to the correct subnet.
If you are an NT administrator, you'll find many improvements in Windows Server 2003 that were carried over from Windows 2000. These include the following:
Notification-driven zone transfers.
Standard DNS requires secondary name servers to poll a master name server for updates. Windows 2000 and Windows Server 2003 incorporate notification features that let a master name server inform its secondaries when an update has occurred. The secondaries then replicate immediately, greatly shortening convergence times. This feature is based on RFC 1996, "A Mechanism for Prompt Notification of Zone Changes."
Incremental zone transfers.
Standard DNS replication transfers the entire contents of a zone file from a master name server to its secondaries for every update. Windows 2000 and Windows Server 2003 permit a secondary name server to request only those changes that have occurred since the last zone transfer. This significantly reduces replication traffic, making it possible to locate secondary name servers at the end of slow network connections. This feature is based on RFC 1995, "Incremental Zone Transfer In DNS."
Service locator records.
Many services need a way to "publish" their existence so that clients can find them. Windows 2000 and Windows Server 2003 support the service locator, or SRV, resource record. The SRV record specifies a service name, its protocol (TCP or UDP), its port number, and the server or servers where it can be found. This feature is based on RFC 2782, "A DNS RR for specifying the location of services (DNS SRV)."
Active Directory Integrated zones.
DNS resource records can be stored in the Active Directory and updated by any domain controller running DNS. This eliminates the bottleneck of a single primary master server in standard DNS. This feature is proprietary to Windows 2000 and Windows Server 2003.
Negative query caching.
All DNS clients cache query results to minimize load on the name servers and reduce network traffic. Windows 2000 and Windows Server 2003 both support caching of negative query responses. This prevents a client from repeatedly querying for a record that does not exist. This feature is based on RFC 2308, "Negative Caching of DNS Queries (DNS NCACHE)."
Secure DNS Updates.
Dynamic DNS Updates can be limited exclusively to trusted clients. This helps prevent attacks designed to populate a zone with false resource records that could send users or user data to unsecured locations. There are two primary Standards Track RFCs that describe how to perform secure DNS Updates: RFC 2535, "Domain Name System Security Extensions," and RFC 2930, "Secret Key Establishment for DNS." Windows 2000 does not support these RFCs at all and Windows Server 2003 only provides basic support. Secure DNS Updates in Windows Server 2003 continue to use the proprietary method introduced in Windows 2000.