How do I block a specific IP from my server?

windows Firewall

First, you will need to open the IPSec snap-in:

1. Start -> Run -> mmc
2. File -> Add/Remove Snap-in...
3. Add...
4. IP Security Policy Management (Not to be confused with IP Security Monitor)
5. Local Computer

Highlight Security Policies on Local Computer

1. In the right pane, right-click and choose Create IP Security Policy...
2. This will start the IP Security Policy Wizard.
3. Choose Next Enter a Name: and Description:
4. UN-CHECK Activate the default response rule. Leave Edit properties checked
5. and click Finish

Under Rules choose Add... This will start the Security Rule Wizard.

1. Hit Next
2. This rule does not specify a tunnel.
3. Local area networks (LAN)
4. This will open the IP Filter List
5. Choose Add...
6. Enter a Name: and Description: Use the IP as the name for identification purposes.
7. Choose Add...
8. Next
9. Description: is optional here, though I'd put the IP to block again...
10. UN-CHECK Mirrored. match packets with the exact opposite source and destination address.
11. For Source address: Use the Drop-down to choose A specific IP Address and enter the IP address to IP to be blocked.
12. Next
13. For Destination address: Use the Drop-down to choose My IP Address
14. Next
15. For Select a protocol type: leave the drop-down on Any
16. Next
17. Make sure Edit properties is unchecked and Click Finish

This will return you to the IP Filter List press O to close it.

1. You will now see and should select the radial for the filter list you just created.
2. Next
3. This will open Filter Action
4. Choose Add...
5. Next
6. Enter a Name: and Description: This action is simply for blocking traffic so name it BLOCK
7. Next
8. Select the Block radial
9. Next
10. Make sure 'Edit properties' is unchecked and Click Finish

This will return you to the Filter Action selection You will now see and should select the radial for the filter action you just created. Make sure 'Edit properties' is unchecked and Click 'Finish'

Click OK to close the Policy you've just created.

The new policy should now show up in the right pane... to activate it, simply right-click and choose assign

More information can be found in this downloadable guide from Microsoft: here