RE: [cobalt-users] CNAME

["Colin J. Raven" <cjraven@xxxxxxxxxxx>]

> Can somebody explain me what a CNAME option is in the DNS server
> of a cobalt raq3 ??
>
> What does it do and what can you do with it ??
>
CNAME is evil, but occasionally has its uses...limited uses as you will see.

CNAME records are "canonical name" records. DNS allows machines to have a
true (canonical name), as well as an unlimited number of aliases. The CNAME
record takes care of aliases. These should only be used when absolutely
necessary, unless you are very familiar with DNS, since they can cause lots
of problems if not used properly.

The Canonical Name (CNAME) record is used to define an alias host name.

A CNAME record takes the following format:

alias.domain.name.      IN      CNAME   otherhost.domain.name.

This defines alias.domain.name as an alias for the host whose canonical
(standard) name is otherhost.domain.name.
Note: A hostname that exists as a CNAME cannot have any other DNS records
applied to it. For example, if your domain is called philosophy.arizona.edu,
and it is separately nameserved (so that it has its own SOA and NS records),
then you cannot give philosophy.arizona.edu a CNAME record. To send mail to
anyuser@xxxxxxxxxxxxxxxxxxxxxx, you need to use MX and/or A records.

One of the times where CNAME records can be useful is when you want a
subdomain to point to a computer outside of your domain. For example, you
might want "news.mydomain.com" to go to your ISP's newsserver. Instead of
putting in the IP address, you could put in "news.mydomain.com CNAME
news.myisp.com", so that if the IP address of the newsserver changed, you
wouldn't have to make any changes.

It is also said that CNAMEs may be useful when you are renaming a host, and
will later get rid of the current name [RFC1912 2.4].

Finally, [RFC1912 2.4] suggests that CNAMES are good for generic names, for
example, having "www.mydomain.com CNAME funky.mydomain.com", so the machine
can have its own official name, but users can still find it without knowing
its real name. Be careful with this though as stated above!!!! In this case,
you can have an A record for www.mydomain.com pointing to the IP address
that funky.mydomain.com has (however, a reverse DNS lookup for the IP
address can only return one of the names).

HTH,
-Colin
--
Colin J. Raven