block all traffic to/from a domain by Bash Script

Target:

• Create a Bash script to block all traffic to/from a domain Youtube by resolving its IPs , then save the info to a file.

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Setup Environment

1. First of all I create a directory for the task and create the script file with the extension .sh

   

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Write Script

#!/bin/bash

DOMAIN="youtube.com"
OUTPUT_FILE="blocked_domains.txt"


IPs=$(dig +short "$DOMAIN" | grep -Eo '([0-9]{1,3}\.){3}[0-9]{1,3}')

if [ -z "$IPs" ]; then
    echo "Failed to resolve $DOMAIN"
    exit 1
fi

for IP in $IPs; do
    sudo iptables -A OUTPUT -d "$IP" -j REJECT
    sudo iptables -A INPUT -s "$IP" -j REJECT
    echo "$DOMAIN ($IP) has been blocked"
    echo "$(date): $DOMAIN ($IP) blocked" >> "$OUTPUT_FILE"
done

echo "Blocking complete. Details saved in $OUTPUT_FILE."

chmod 777 script.sh
sudo ./script.sh

1. First I specify the domain I want to block , in this case I will choose youtube.com

2. Then I assign an IP variable and use the regex to extract the IP

3. If the domain couldn't be resolved, the script exits with a message

4. Then I block the outgoing & the ingoing traffic from this domain using iptables

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Test

cat blocked_domains.txt 
Sun Oct  5 07:41:17 PM EDT 2025: youtube.com (172.217.21.14) blocked

go to youtube.com