example.com is a registered domain name. Externally, there are nameservers associated with example.com which include an A record for subdomain.example.com which points to an externally hosted web page.
Internally, we have example.com as an ActiveDirectory domain. We wanted to utilise subdomain.example.com internally as well. We have therefore added a matching A record to the internal DNS.
Externally to the network, everything works fine.
When utilising nslookup for subdomain.example.com internally, it returns the correct IP address.
Pinging subdomain.example.com internally, results in the correct external resource responding.
When visiting the page in the browser, it provides page cannot be displayed (IE11) or ERR_CONN_RESET (Chrome).
I am looking for suggestions on what to look at next.