CNAME (Canonical Name) is a type of DNS record that used as alias for another domain.
DNS (Domain Name System) is a service that translates domain names into IP addresses. Users can easily remember domain names, but he computers understand IP addresses that’s why we need DNS. For example, without this service, you have to type '126.96.36.199' in your browser instead of www.facebook.com to access Facebook. IP - Domain mappings are kept on DNS servers. You can query those matches on securityforeveryone.com
There is two type of IP addresses IPv4, and IPv6. IPv4 address looks like these:
188.8.131.52 127.0.0.1 255.255.255.255
IPv6 addressed looks like these (all of them are the same IP):
::ffff:808:808 0:0:0:0:0:ffff:0808:0808 0000:0000:0000:0000:0000:ffff:0808:0808
CNAME (Canonical Name) is a type of DNS record that is used as an alias for another domain. Let's give a real-life example. You bought a domain such as securityforeveryone.com then you offer an online email services. To do that you've created a new subdomain such as mail.securityforeveryone.com. However, you found out that some of mail clients use webmail subdomain as default. In that case, you can use a CNAME records to map webmail.securityforeveryone.com to mail.securityforeveryone.com. CNAME records must point to a domain name not an IP addresses.
Also, another example of using CNAME records is using multiple ports of same IP addresses. You can use ftp.securityforeveryone.com (21), tomcat.securityforeveryone.com (8080), apache.securityforeveryone.com (80,443) on the same IP addresses. All of them can point securityforeveryone.com in the CNAME records. With that, when you move your server to another ip addresses you have to change securityforeveryone.com's A record only.
Simple. Write your domain on the form that top of the page, that's all. Generally, people use CNAME to points another subdomain or main domain. You can use DNS CNAME lookup tool to get them.
Or if you are using a Linux or an OS X operating system, open terminal and type dig -t cname yourdomain.com. If your domain has a valid cname record, it would look like that:
dig -t cname securityforeveryone.com ;; ANSWER SECTION: www.securityforeveryone.com. 168 IN CNAME securityforeveryone.com.
If you are using Windows open powershell and type Resolve-DnsName -Name yourdomain.com -Type cname
If you can not see CNAME records that you want, you need to go where you manage the DNS records (usually the hosting provider panel) and check CNAME records. Do not forget that, CNAME records must be a domain name. And must be the only records for related subdomain.
Also, if your CNAME record shows another domain name, make sure that domain name is registered by you. If it falls into the hands of malicious people, you may experience a violation of information security.