C.3.2.4 "CNAME" Records

CNAME resource records provide an alias feature similar to the aliasing capability found in the HOSTS file.

DNS servers based on BIND use the format shown in Figure C.14 for the CNAME resource record:

 Mailhost  IN  CNAME  Greywolf

Figure C.14 Sample "CNAME" record, pointing to the host named "Greywolf".

If a system attempts to connect to "Mailhost.UNOVERICA.COM" then they will be redirected to "Greywolf." Their DNS client will then issue a lookup on "Greywolf," attempting to locate the IP address for that host.

CNAME records can be recursive, up to seven levels deep. The CNAME record for "Mailhost" could easily point to "FooBar" which would simply be another CNAME record, pointing to yet another host.

To simplify life for your local POP3 users, you may wish to use a CNAME record called "mailhost" or something similar. This would allow you to move mail services around on the network without having to reconfigure your POP3 mail clients. However, it is not a good idea to publish a CNAME as an MX record. Many SMTP mail servers do not support this functionality, and you would not receive mail from those systems.

For more information about the Address record, refer to section C.3.2.1 "A" Records. For more information about the Mail Exchange record, refer to section C.3.2.2 "MX" Records. For more information about the Text record, refer to section C.3.2.3 "TXT" Records. For more information about DNS' architecture, refer to section C.3.1 DNS' Hierarchy.

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