Whitelist an IP address in IPTables.
How to whitelist IP address 192.168.0.1
Step 1: Log into the server via SSH.
Step 2: Allow incoming connections from 192.168.0.1
# iptables -A INPUT -s 192.168.0.1 -j ACCEPT
Step 3: Allow outgoing connections to 192.168.0.1
# iptables -A OUTPUT -d 192.168.0.1 -j ACCEPT