Appendix D: DNS Records

• A—The A (address) resource record maps a host (computer or other network device) name to an IP address in a DNS zone. Its counterpart, the PTR resource record, is used to map an IP address to a host (computer or other network device) name in a DNS reverse zone (those in the In-addr.arpa DNS domain).
• AFSDB—The AFSDB resource record gives the location of either an AFS (Andrew File System) cell database server, or a DCE (Distributed Computing Environment) cell's authenticated name server. Transarc's AFS is a network file system, similar to NFS, but designed more for wide-area networks (WANs). The AFS system uses DNS to map a DNS domain name to the name of an AFS cell database server. The Open Software Foundation's DCE Naming service uses DNS for a similar function: mapping the DNS domain name of a DCE cell to authenticated name servers for that cell.
• CNAME—The CNAME (canonical name) resource record creates an alias (synonymous name) for the specified host (computer or other network device) name. You can use CNAME records to hide the implementation details of your network from the clients that connect to it. For example, Ftp.microsoft.com is an alias (CNAME) for the real name of the computer that runs the FTP server for Microsoft. Clients connect to Ftp.microsoft.com without regard for the real name of the computer. This also allows the FTP server to be moved to a different computer; only the CNAME record needs to change.
• HINFO—The HINFO (host information) resource record identifies a host's (computer or other network device) hardware type and operating system. The CPU Type and Operating System identifiers should come from the MACHINE NAMES and SYSTEM NAMES listed in RFC 1700 (Assigned Numbers).
• ISDN—The ISDN (Integrated Services Digital Network) resource record is a variation of the A (address) resource record. Rather than mapping a host (computer or other network device) name to an IP address, the ISDN record maps the name to an ISDN address. An ISDN address is a phone number that consists of a country code, an area code or country code, a local phone number, and, optionally, a subaddress. The ISDN resource record is designed to be used in conjunction with the RT (route through) resource record.
• MB—The MB (mailbox) resource record is an experimental record that specifies a DNS host (computer or other network device) with the specified mailbox. Other related experimental records are the MG (mail group) resource record, the MR (mailbox rename) resource record, and the MINFO (mailbox information) resource record.
• MG—The MG (mail group) resource record is an experimental record that specifies a mailbox that is a member of the mail group (mailing list) specified by the DNS domain name. Other related experimental records are the MB (mailbox) resource record, the MR (mailbox rename) resource record, and the MINFO (mailbox information) resource record.
• MINFO—The MINFO (mailbox information) resource record is an experimental record that specifies a mailbox that is responsible for the specified mailing list or mailbox. Other related experimental records are the MB (mailbox) resource record, the MG (mail group) resource record, and the MR (mailbox rename) resource record.
• MR—The MR (mailbox rename) resource record is an experimental record that specifies a mailbox that is the proper rename of the other specified mailbox. Other related experimental records are the MB (mailbox) resource record, the MG (mail group) resource record, and the MINFO (mailbox information) resource record.
• MX—The MX (mail exchanger) resource record specifies a mail exchange server for a DNS domain name. A mail exchange server is a host (computer or other network device) that will either process or forward mail for the DNS domain name. Processing the mail means either delivering it to the addressee or passing it to a different type of mail transport. Forwarding the mail means sending it to its final destination server, sending it using Simple Message Transfer Protocol (SMTP) to another mail exchange server that is closer to the final destination, or queuing it for a specified amount of time.
• NS—The NS (name server) resource record identifies the DNS name server(s) for the DNS domain. NS resource records appear in all DNS zones and reverse zones (those in the In-addr.arpa DNS domain).
• PTR—The PTR (pointer) resource record maps an IP address to a host (computer or other network device) name in a DNS reverse zone (those in the In-addr.arpa DNS domain). Its counterpart, the A (address) resource record, is used to map a host (computer or other network device) name to an IP address in a DNS zone.
• RP—The RP (responsible person) resource record indicates who is responsible for the specified DNS domain or host (computer or other network device). You can specify multiple RP records for a given DNS domain or host. The record has two parts: an electronic mail address (in the same DNS format as the one in the SOA resource record), and a DNS domain name that points to additional information about the contact.
• RT—The RT (route through) resource record specifies an intermediate host (computer or other network device) that routes packets to a destination host. The RT record is used in conjunction with the ISDN and X25 resource records. It is syntactically and semantically similar to the MX record type and is used in much the same way.
• SOA—The SOA (start of authority) resource record indicates that this DNS name server is the best source of information for the data within this DNS domain. It is the first record in each of the DNS database files. The SOA resource record is created automatically by DNS Manager when you create a new DNS zone.
• TXT—The TXT (text) resource record associates general textual information with an item in the DNS database. A typical use is for identifying a host's (computer or other network device) location (for example, Location: Building 26S, Room 2499). The text string must be less than 256 characters, but multiple TXT resource records are allowed.
• WKS—The WKS (well-known service) resource record describes the services provided by a particular protocol on a particular interface. The protocol is usually UDP or TCP, but can be any of the entries listed in the PROTOCOLS file (\%SystemRoot%\system32\drivers\etc\protocol). The services are the services below port number 256 from the SERVICES file (\%SystemRoot%\system32\drivers\etc\services).
• X25—The X25 (X.25) resource record is a variation of the A (address) resource record. Rather than mapping a host (computer or other network device) name to an IP address, the X25 record maps the name to an X.121 address. X.121 is the International Standards Organization (ISO) standard that specifies the format of addresses used in X.25 networks. The X25 resource record is designed to be used in conjunction with the RT (route through) resource record.
• Generic Record—The generic resource record is used to add a non-standard resource record to the DNS database. The generic resource record is a feature of Microsoft DNS Manager.