I had this same issue and here are the specific configuration that I needed to get this to work.
First, go to the VirtualBox preferences -> Network.
For the "Host-only Networks" tab, focus on the vboxnet0.
Click the icon on the left that looks like a screwdriver.
For the Adapter tab, fill in the IPv4 Network Address as 192.168.56.1
Fill in the IPv4 Network Mask as 255.255.255.0
For the DHCP Server tab, select the check box for Enable Server to enable the server
Fill in the Server Address as 192.168.56.100
Fill in the Server Mask as 255.255.255.0
Fill in the Lower Address Bound as 192.168.56.101
Fill in the Upper Address Bound as 192.168.56.254
The DHCP server part is what was not correct for me and it fixed my problem.
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