[Environment] 

Any Samsung device supporting the Knox framework.

[Summary]

Your firewall must allow HTTPS traffic between the device management server and Samsung’s Attestation service. The device management server initiates each session.

The general Attestation API domain is attest-api.secb2b.com. There are also three region specific domains.

China region — china-attest-api.secb2b.com.cn
European region — eu-attest-api.secb2b.com 
US region — us-attest-api.secb2b.com

Depending on your location and EMM configuration, you need to allow traffic to one, or several of these domains.