IIS 6: The Complete Reference

In addition to holding zones, WS03 can also act as a caching server. A caching server does not hold any zone information. It simply acts as a DNS server for clients and resolves names for those clients. When it resolves a name, the caching server retains that name and IP in the cache so that information is ready for the next query.

The WS03 DNS server acts as a caching server by default. If you create zones on the DNS server, it will still perform caching-it just won't be strictly a caching server anymore.

Resource Record Types in DNS

DNS offers several different resource record types that are used to identify different types of servers or applications. The resource record types are listed here.

A Address record. This record type is used to identify a host resource record. It maps a DNS domain name to an IPv4, 32-bit address.

AAAA The record type to identify a host address resource record for IPv6. This maps a DNS domain name to an IPv6, 128-bit address.

AFSDB Andrew File System Database resource record. This maps a DNS name to an AFS database server.

ATMA Asynchronous Transfer Mode Address resource record. This maps a DNS domain name to an ATM address.

CNAME Canonical Name resource record. This maps a DNS name to another DNS name. This is used for aliasing one name to another. The aliased DNS name must exist in that domain.

HINFO Host Information resource record. This specifies the type of CPU and operating system for a host record. This information can be used by application protocols, such as FTP, that sometimes use different procedures with certain CPUs or operating systems.

ISDN Integrated Services Digital Network resource record. This maps a DNS domain name to an ISDN telephone number.

KEY Public Key resource record. This contains a public key for the zone named in this record.

MB Mailbox resource record. This maps a domain mailbox name to a mailbox host name. The mailbox host name must be the same as a valid host address (A) resource record already used by a host in the same zone.

MG Mail Group resource record. This is used to specify mailbox resource records for a domain mailing group. The mailbox (MB) resource records must exist in the current zone.

MINFO Mailbox Mail List Information resource record. This is used to specify the mailbox of a responsible party for a mailbox or mailing list. The mailbox (MB) resource records must exist in the current zone.

MR Mailbox Renamed resource record. This specifies a mailbox resource record that corresponds to another mailbox. An MR resource record is typically used to forward mail for a user who has moved to a different mailbox.

MX Mail Exchanger resource record. This identifies a mail server that can accept mail for the current zone. A two-digit priority indicates preferred ordering if multiple exchanger hosts are specified. Each server named in an MX record must have a corresponding host (A) address resource record.

NS Name Server resource record. This record maps a DNS domain name to a server responsible for that domain. The server specified must have a corresponding host (A) address resource record.

NXT Next resource record. This is used to deny the existence of a record in a domain by creating a chain of all the owner names in that zone.

OPT Option resource record. This adds option data to either a DNS request or a response.

PTR Pointer resource record. This points from one name to another name in a different zone. This is used extensively for the in-addr.arpa domain tree to provide reverse lookups of address-to-name mappings.

RP Responsible Person resource record. This specifies the domain mailbox name for a responsible person. This responsible person is listed as being responsible for that zone.

RT Route Through resource record. This provides an intermediate host binding for internal hosts that do not have a direct access to an external network connection. Like the MX record, a two-digit preference value is used to set priority if multiple intermediate routing hosts are specified and a corresponding host (A) address resource record must be in the current zone.

SIG Signature resource record. This record encrypts a resource recordset to a domain name.

SOA Start of Authority resource record. This indicates the name of the server that is the primary name server responsible for that zone. This record is the first record in a zone. It contains the following information:

• serial number The version of this zone in use

• refresh The time, in seconds, that a secondary server waits before renewing the zone information from the primary server

• retry The time, in seconds, that a secondary server waits before retrying a failed zone transfer

• expire The time, in seconds, that a server stops responding to queries and considers its zone information invalid if a zone transfer has not taken place

• min TTL The default TTL of the records in the zone

SRV

Service Locator resource record. This allows multiple servers providing a similar TCP/IP-based service to be easily located. This record maintains a list of servers for certain services so that the services can be located by using a single DNS query operation. The servers can even be ordered by preference for a DNS domain name. This is how clients locate Windows Active Directory Servers, because a SRV record lists the domain controllers that use the Lightweight Directory Access Protocol (LDAP) service over TCP port 389.

Several fields lie within the SRV record:

• Service The name of the service. Well-known services have predefined names and are defined in RFC 1700. You can make any name you wish, but if a predefined name is defined, it must be used to meet standards.

• Protocol Indicates the transport protocol type. By default, you can choose from TCP or UDP. RFC 1700 defines other protocols that can also be used.

• Name The DNS domain name for this service record. The SRV resource record name is unique among other DNS record types.

• Priority Sets the priority for the host specified in this record. Clients attempt to contact the first reachable host of the lowest numbered preference listed here.

• Weight Sets the weight for the server specified in this record. If more than one server exists with the same priority, clients can use the weight to choose between servers. This field is optional.

• Port Specifies the port used by the service indicated in the Service field. Well- known ports are specified in RFC 1700. Ports can be selected in the range of 0 to 65535.

• Target Specifies the DNS domain name of the host for this service. Host names must have a valid host (A) record in that DNS domain.

TXT Text resource record. This record can contain a description or additional information about the zone.

WKS Well-Known Service resource record. This contains a list of the well-known TCP/IP services supported by a particular protocol (TCP or UDP) on a specific IP address.

X25 X.25 resource record. This maps a DNS domain name to a Public Switched Data Network (PSDN) number.