external subdomain opening to main domain instead of the subdomain

I have multsite sub-domain setup at geoboxer.com It is hosted on a static ip through A record from an external dns server.

I have multiple subsites working. I needed to point subdomain.domain.com to open up on subdomain.geoboxer.com. That external domain resides on my dns server. I have created a CNAME on my dns server with subdomain.domain.com pointing to subdmain.geoboxer.com

After that whenever I try to access that subsite through any url it takes me to the signup page of my multisite root.

Confused on what I am doing wrong here. Please help.