This is an odd KB article from Microsoft for Hyper-V. It deals with a virtual machine that is running on on Hyper-V Server 2012 or Hyper-V Server 2012 R2. The VM is configured to use the DLC protocol but the VM cannot connect to an SNA host.
You use Microsoft Hyper-V Server 2012 or Microsoft Hyper-V Server 2012 R2 to host a virtual machine such as for Microsoft Host Integration Server 2009. If the virtual machine is configured to use the Data Link Control (DLC) protocol to connect to a Systems Network Architecture (SNA) host such as an IBM Mainframe z/OS system, the connection fails.
This problem occurs because Hyper-V Server 2012 and Hyper-V Server 2012 R2 do not support 802.3 frame types that do not have a Sub-Network Access Protocol (SNAP) header.
A hotfix is available from Microsoft to resolve this issue.