In order to block a specific IP address, you need to add a Firewall filter rule.

Step-by-step guide

Follow these steps to add filter rule using Winbox:

1. Go to IP>Firewall;
2. Select tab "Filter rules";
3. Click on the + to add new rule;
4. Select tab "General";
5. Choose Chain: Input;
6. Select Src. Address - input your desired IP;
7. Select tab "Action";
8. Choose Action: Drop;
9. Click OK, and the desired IP address will be blocked by a firewall filter. 

Chain input limits the connection to the device itself. To limit traffic going through the device use chain "forward". Further please read on how to build your first firewall.

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