Can't delegate my DNS server into Link Controller

You haven't actually created a record for www.gtm.test.com on your DNS server. All you've done is created an alias for www.test.com pointing to www.gtm.test.com

 

 

You should create a record like the below. By the way, I'm making the assumption that we're in the DNS zone "gtm.test.com"

 

 

www IN NS ns1

 

 

Now, when a user queries your "WWW" record, your DNS server delegates resolution to ns1 (your self-ip on the LinkController)

 

 

In case you want to see it in a FQDN fashion,

 

 

www.gtm.test.com IN NS ns1.gtm.test.com