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A Canonical Name record (abbreviated as CNAME record) is a type of resource record in the Domain Name System (DNS) used to specify that a domain name is an alias for another domain, the "canonical" domain. All information, including subdomains, IP addresses, etc., are defined by the canonical domain. This can prove convenient when running multiple services (like an FTP server ''and'' a webserver; each running on different ports) from a single IP address. One can, for example, point ftp.example.com and www.example.com to the DNS A record for example.com, which in turn points to the IP-address. Then, if the IP-address ever changes, one only has to record the change in one place within the network: in the DNS A record. CNAME records must always point to another domain name, never directly to an IP-address. == Details == DNS CNAME records are specified in RFC 1034 and clarified in Section 10 of RFC 2181. CNAME records are handled specially in the domain name system, and have several restrictions on their use. When a DNS resolver encounters a CNAME record while looking for a regular resource record, it will restart the query using the canonical name instead of the original name. (If the resolver is specifically told to look for CNAME records, the canonical name (right-hand side) is returned, rather than restarting the query.) The canonical name that a CNAME record points to can be anywhere in the DNS, whether local or on a remote server in a different DNS zone. For example, if there is a DNS zone as follows: NAME TYPE VALUE -------------------------------------------------- bar.example.com. CNAME foo.example.com. foo.example.com. A 192.0.2.23 when an A record lookup for bar.example.com is done, the resolver will see a CNAME record and restart the checking at foo.example.com and will then return 192.0.2.23. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「CNAME record」の詳細全文を読む スポンサード リンク
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