Essential Linux iptables Rules Every Sysadmin Should Know

Below are some commonly used Linux iptables rules; adjust them to your specific needs.

# 1. Delete all existing rules

# 2. Set default chain policy

# 3. Block a specific IP address

# 4. Allow all incoming SSH

# 5. Allow SSH from a specific network

# 6. Allow incoming HTTP

# 7. Multiple ports (allow incoming SSH, HTTP, HTTPS)

# 8. Allow outgoing SSH

# 9. Allow outgoing SSH to a specific network

# 10. Allow outgoing HTTPS

# 11. Load balance incoming HTTPS traffic

# 12. Internal to external ping

# 13. External to internal ping

# 14. Allow loopback access

# 15. Allow packets from internal network to external

# 16. Allow outgoing DNS

# 17. Allow NIS connections

# 18. Allow rsync from a specific network

# 19. Allow MySQL connections from a specific network

# 20. Allow Sendmail or Postfix

# 21. Allow IMAP and IMAPS

# 22. Allow POP3 and POP3S

# 23. Prevent DoS attacks

# 24. Forward port 422 to port 22

# 25. Log dropped packets