Product : Microsoft, HyperV/2019, DataCenter
Feature : Network Extensions, 7, Extensions
Content Owner:  Roman Macek
Summary
Hyper-V Extensible Switch - 3rd party Extensions (Nexus 1000V - Fee-Based Add On)
Details
(No major updates in WS 2016) The Hyper-V Virtual Switch enables ISVs to create extensible plug-ins (Virtual Switch Extensions) that can provide enhanced networking and security capabilities.
Deatils on Ciscos 1000v for Hyper-V here: http://bit.ly/1aZTXOk

New in 2012 R2 is the ability to give third party extensions visibility into both Hyper-V Network Virtualization address spaces.
The HNV module was moved to inside the virtual switch so that extensions could see both the provider (PA) and virtual (CA) IP address spaces. This allows forwarding and other types of extensions to make decisions with knowledge of both address spaces.
The second change was to implement hybrid forwarding. Hybrid forwarding directs packets to different forwarding agents, based upon the packet type. In the Windows Server 2012 R2 implementation a packet that is NVGRE is forwarded by the HNV module. A packet that is non-NVGRE is forwarded as normal by the forwarding extension. Regardless of which agent performs the forwarding computation, the forwarding extension still has the opportunity to apply additional policies to the packet. If there is no forwarding extension, the Microsoft forwarding logic takes over for non-NVGRE packets.

Details here: http://bit.ly/1aZTz2p