# Internet Redirect & Alias: The CNAME

- Link: https://www.agilicus.com/about-dns-cname/
- Published: 2021-01-18T02:17:17+00:00
- Author: Don Bowman

You have probably used a product which used, or seen talk of, a CNAME. What is this?
Why would you want it? How would you configure it? What does it do? When would you
use it?

A _CNAME_ is a “[Canonical Name Record](https://en.wikipedia.org/wiki/CNAME_record)“.
It is an entry in an Internet Name Server that maps one name onto another. In a 
nutshell, an alias. They were originally created to allow running multiple services
on the same host (e.g. ‘www’ and ‘ftp’ and ‘smtp’). CNAME’s were standardised in
[RFC 1034](https://tools.ietf.org/html/rfc1034) in 1987. Perhaps before you were
born!

As an adminstrator, the most common use the CNAME has today is for services provided
by a 3rd party that use your domain name. An example would be a Web Application 
Firewall. You might purchase such as service from a 3rd party, and, want them to
handle the traffic to www.example.com. So, you would create a CNAME for www.example.
com pointing to fw.waf.com, if they were called ‘waf.com’. This means that when 
one of your users opens their browser and types in ‘www.example.com’, they get back
a record saying “if you really want to know where that is, we suggest looking up
fw.waf.com”.

Why would you use a CNAME for this, rather than an A record (address, e.g. an IP
address)? Well, ‘waf.com’ might have big plans. Someday they will move out of their
parent’s basement and into a real cloud provider. They will have hundreds of servers
in tens of countries. They don’t want to have to have all customers update DNS records
for this growth. So, by giving you a pointer to something they control, waf.com 
can make their updates independent of you, the administrator of example.com.

How do you configure a CNAME? Well, it will depend on your DNS provider. It is very
likely they have a web-based interface, and it might vary. Below is how I would 
configure a CNAME for ‘*.cloud.example.com’ pointing to ‘ca-1.agilicus.ca’. Where
did ‘example.com’ go in this screenshot you ask? Well, it is implicit, I am configuring
the DNS for example.com, so the records omit that.

What does ‘*.cloud’ mean? Well, it means that foo.cloud.example.com, bar.cloud.example.
com will both (and any name) resolve to ca-1.agilicus.ca.

[⌊Google DNS CNAME⌉⌊Google DNS CNAME⌉[

Now, how would you confirm you have created your CNAME properly? My favourite method
is the command-line and a tool called ‘dig’.

    ```wp-block-preformatted
    $ dig -t cname foo.cloud.zero-trust.ca
     ; <<>> DiG 9.16.6-Ubuntu <<>> -t cname foo.cloud.zero-trust.ca
    ...
     ;; QUESTION SECTION:
     ;foo.cloud.zero-trust.ca.    IN  CNAME
     ;; ANSWER SECTION:
     foo.cloud.zero-trust.ca. 3600    IN  CNAME   ca-1.agilicus.ca.
    ```

But, you can also use online web sites that will help you, e.g. [https://dnslookup.online](https://dnslookup.online/cname.html).
You can see the result below. DNS takes time to propogate, so give it a few minutes.
Also, the TTL (time to live) controls how long others will cache this. If in doubt,
make this 5 minutes until you have your CNAME setup properly, and then use a longer
time like 1 hour.

[⌊c2d8e494-image⌉⌊c2d8e494-image⌉[