|I l@ve RuBoard|
2.20 Making Your Services Easy to Find
Give your servers "functional" domain names. For example, most users will expect to find an organization's FTP server at the domain name ftp.domain-name-of-zone. In most cases, the domain name can be an alias for the canonical name of the host running the service; that's not possible with name servers or mail servers, though.
Other common functional domain names include:
One big benefit of using functional domain names is that you can move a service from one host to another by changing only the A or CNAME record for the functional domain name, and without changing the configuration of every client of that service. For example, if you moved your NTP server from a.foo.example to b.foo.example, you could just change the ntp.foo.example CNAME record to:
ntp.foo.example. IN CNAME b.foo.example.
Assuming you'd configured your NTP clients to refer to your NTP server by the domain name ntp.foo.example, you wouldn't have to make any changes to your clients' configuration.
The domain names of mail servers and name servers are special because of the way they're used. The domain name of a name server will usually appear in an NS record, delegating a zone to that name server. A name server sending that NS record in a referral will only add A records for the name server's domain name to the response. If the domain name owns a CNAME record, the name server won't find it.
Likewise, mail servers sending mail to your email addresses expect to find A records for the mail servers you list in your MX records. If you use CNAME records, they won't find the address they're after.
Also, if one of your backup mail servers receives the email, it will "trim" the list of MX records by removing itself and any less-preferred mail servers. If it doesn't recognize itself in the list because you've used an alias in an MX record, it may try to send mail to itself, or to a less-preferred mail server.
|I l@ve RuBoard|