In this blog I will discuss what the NetFT Virtual Adapter Performance Filter in Windows Server 2012 and Windows Server 2012 R2 is and the scenarios when you should or should not enable it.
The Microsoft Failover Cluster Virtual Adapter (NetFT) is a virtual adapter used by the Failover Clustering feature to build fault tolerant communication routes between nodes in a cluster for intra-cluster communication.
When the Cluster Service communicates to another node in the cluster, it sends data down over TCP to the NetFT virtual adapter. NetFT then sends the data over UDP down to the physical network card, which then sends it over the network to another node. See the below diagram:
When the data is received by the other node, it follows the same flow. Up the physical adapter, then to NetFT, and finally up to the Cluster Service. The NetFT Virtual Adapter Performance Filter is a filter in Windows Server 2012 and Windows Server 2012 R2 which inspects traffic inbound on the physical NIC and then reroutes cluster traffic addressed for NetFT directly to the NetFT driver. This bypasses the physical NIC UDP / IP stack and delivers increased cluster network performance.
When to Enable the NetFT Virtual Adapter Performance Filter
The NetFT Virtual Adapter Performance Filter is disabled by default. The filter is disabled because it can cause issues with Hyper-V clusters which have a Guest Cluster running in VMs running on top of them. Issues have been seen where the NetFT Virtual Adapter Performance Filter in the host incorrectly routes NetFT traffic bound for a guest VM to the host. This can result in communication issues with the guest cluster in the VM. More details can be found in this article: