VirtualBox static IP address on a host-only network

I have a number of CentOS 7 servers that comprise a FreeIPA domain on a VirtualBox host-only network. Whenever I start a server though, it is liable to pick up an IP address that I’ve already assigned to another server (which is currently powered off) in /etc/hosts.

How do I assign it a specific static IP address?

In CentOS 7, you can use the Network Manager Text User Interface (nmtui) to edit the network settings. Here’s the first thing I tried, which wasn’t quite right:

# nmtui

• Edit a connection
• Select a connection, e.g. enp0s3
• IPv4 Configuration
• Change from Automatic to Manual
• Select Show
• Enter 192.168.56.109/32 for addresses
• Enter 192.168.56.255 for the gateway

When I used those settings, it didn’t work. No route to host, etc. I looked at the network interface settings via a different method:

# ip addr show

The brd (broadcast) address listed was the same as my ip address, 192.168.56.109, which was unexpected and probably why it wasn’t working!

I ran nmtui again and changed the address from 192.168.56.109/32 to 192.168.56.109/24 and it worked.

Since the /32 is interpreted as the subnet mask, it created a subnet with an address range of 1, and the broadcast address would be the same as the ip address. Specifying a subnet mask of /24 creates a subnet with 256 addresses, and a broadcast address of 192.168.56.255 (the same as was listed for the other machines on the virtual network that were using DHCP).