Then you have either the host or yourself that doesn't have their console port forwarded correctly. Check you console settings see what you NAT type is and check within the game itself. COD has a port specific to it that needs to be forwarded as well. Not sure your platform but a list is here.
https://portforward.com/call-of-duty-black-ops-iiii/
On xbox the 3075 is specific to COD.
Toss 3076 onto this too. I normally set it as TCP/UDP 3074-3076.