Basically what you’re going to do is create a new virtual network on your Hyper-V machine, add a new NIC to your VMs and then put them on the same network.


STEP 1 – CREATE A NEW VIRTUAL NETWORK (switch and NIC)


The first thing you need to do is create a new virtual network. From within Hyper-V, select Virtual Network Settings. Create a new INTERNAL network and leave all the default options.
What this does is create a new network within Hyper-V and creates a virtual NIC adapter on the host machine.


STEP 2 – CONFIGURE THE NIC ON THE HOST MACHINE


With the virtual NIC created on the host, you want to change its' IP settings. You can use a network you know you'll never use:
IP – 192.168.1.20
Subnet – 255.255.255.0
Leave everything else blank / default. 

Rename this NIC adapter to Hyper-V INTERNAL to make it easy to find later.
At this point the host machine is setup and ready for action!


STEP 3 – ADD A NEW NIC ON THE VCL
Now it’s time to setup the guest. First, shut down the guest machine so that it’s not running or in a saved state.
Then, modify the settings of the virtual machine (right-click the virtual machine and pick settings). In the settings dialog select Add New Hardware at the top of the left-panel and select the network you created in step 1 above. Leave all settings as the default options.
With a NIC added to the VM, start the VM up.


STEP 4 – CONFIGURE NIC ON THE VCL


When the VM is turned on, you can now configure the new network adapter From Network -> Interfaces, Press Add. There should be one available interface what to use. Change its' IP settings to put it on the same subnet but with a different IP than the host. For instance:
IP – 192.168.1.21
Subnet – 255.255.255.0