The Hyper-V virtual switch doesn't include a full-fledged firewall, but it does have one of the firewall's most important yet basic features. Access control lists (ACLs) are simple definitions of traffic rules that allow or deny particular communication types. The basic port ACL was introduced to Hyper-V in the 2012 version, and the extended ACL was part of the 2012 R2 release.

A firewall defines its rules from the perspective of the firewall itself. It controls traffic as it passes through. In contrast, a Hyper-V port ACL is defined directly on virtual adapters and works from their perspective. It's important to remember this as you create ACLs.

The key to the ACL is that it is a list. The most meaningful way to use ACLs is by layering them. This is most commonly done by creating a universal rule that blocks all traffic and then creates exceptions.