The cams I have, auth happens over port 80 (or 443 if you use HTTPS) and RSTP happens on port 554. Chances are your NVR is trying to connect to that hostname on TCP 554 and getting rejected by the firewall (if there is one).
Look through your target cam network port menus, and if you can't find the answer there; pull out wireshark to see what ports are getting hit.