First, enable server list view from steam.
Right click steam on the Taskbar > Settings > Interface > SET TASKBAR PREFERENCES > Select the 'Servers' checkbox > OK

1. Right click on the Steam icon from the Taskbar, then click Servers.

2. Select the game.

3. Write down the first 3 sets of numbers from the IP address you wish to block. (later you can set to block all sub addresses under that machine)

For example, if you want to block 46.102.86.5:8888, and 46.102.86.5:7779, then you should block the IP range from 46.102.86.0 to 46.102.86.255. (Ignore the 4-digit port number at the end.)

See this in detail in later section.

Press WIN+R to open the run box.

1. Type and enter: WF.msc

2. Select 'Outbound Rules' from the left panel, then click 'New Rule' from the options panel on the right.
3. Select 'Custom' for the Rule Type, then Next.
4. Select apply to 'All programs', then Next.
5. Leave the Protocol type as 'Any', click Next.
6. For local IP, select 'Any IP address'.

7. For remote IP, select 'These IP addresses:', click Add.
8. Select 'This IP address range' e.g. from: 46.102.86.0, to: 46.102.86.255. (so this means you block all servers hosting on the same machine using 46.102.86.xxx)
9. Next, select 'Block the connection', then continue to the end.

Set up an 'Inbound Rule' with the exact same way as Outbound Rule above for extra safety.