Compare 2 Lists of IP Addresses

#!/bin/bash
# Written by: Leon Trappett
#
# This script will take 2 lists of IP addresses from text files and then list the IP addresses that are common amongst them
# For example from a firewall log and a list of known compromised hosts

countLoopA=0
countLoopB=0

while read unusualIP
do

        while read firewallIP
        do

                if [[ $unusualIP == $firewallIP ]]; then
                        echo "***" $firewallIP
                        break
                fi

                let countLoopA=countLoopA+1

        done < filename1.txt


        let countLoopB=countLoopB+1

#       echo $countLoopB " " $countLoopA


done < filename2.txt