CNAME stands for Canonical Name for a domain. CNAME is an alias records that create association between a sub-domain and antother domain or subdomain.
And, A Record simply creates an association between a domain/sub-domain name and an IP Address.
gallery.bala-krishna.com -> gallery.another-domain.com -> 18.104.22.168
you can see above CNAME require two DNS lookup to translate domain/subdomain to an IP Address. If client request for gallery.bala-krishna.com then DNS record will return gallery.another-domain.com then gallery.another-domain.com has to query DNS to translate gallery.another-domain.com into IP Address.
CNAME Record Syntax:
www? ? 14400? ? IN? ? CNAME? ? bala-krishna.com
Example A Record
gallery.another-domain.com -> 22.214.171.124
In case of gallery.another-domain.com, A record directly point to an IP Address so the DNS lookup directly returns IP Address to the client rather then domain/subdomain. hence only one DNS lookup required.
A Record Syntex:
ftp? ? ? ? 14400? ? IN? ? ? A? ? ? 126.96.36.199