IP Address Change & NMap Scans: Does it Help?

TL;DR

Changing your IP address can temporarily disrupt an NMap scan, but it’s not a reliable long-term solution. A determined attacker will likely find your new IP quickly. Focus on proper firewall configuration and security practices instead.

Understanding the Problem

NMap is a powerful network scanning tool used to discover hosts and services on a computer network. It works by sending packets to target IPs and analysing the responses. If an attacker knows your IP address, they can use NMap to identify open ports and potential vulnerabilities.

Does Changing Your IP Address Stop NMap?

Changing your IP address breaks the direct connection between the attacker’s scan and your current network location. However, this is a short-term fix for several reasons:

• Dynamic IPs: Most home internet connections use dynamic IPs assigned by your Internet Service Provider (ISP). Your IP changes periodically anyway.
• Attacker Persistence: An attacker can monitor DNS records or other online services to identify when your new IP address is active.
• Multiple Attack Vectors: NMap isn’t the only way to find targets. Other methods, like social engineering or exploiting vulnerabilities in websites you visit, could reveal your IP.

Steps to Mitigate NMap Attacks (and why changing your IP is usually insufficient)

1. Firewall Configuration: This is the most effective defence.
   • Block Unnecessary Ports: Only allow traffic on ports required for services you actively use.
   • Use a Firewall: Windows Firewall (built-in), or third-party firewalls like pfSense, ZoneAlarm, etc.
   • Example (Windows Firewall): To block incoming connections on port 22 (SSH):

     netsh advfirewall firewall add rule name="Block SSH" dir=in action=block protocol=TCP localport=22

2. Router Security: Secure your router to prevent unauthorized access.
   • Strong Password: Change the default administrator password.
   • Firmware Updates: Keep your router’s firmware up-to-date.
   • Disable Remote Management (if not needed): This reduces attack surface.
3. Intrusion Detection/Prevention Systems (IDS/IPS): These systems monitor network traffic for malicious activity.
   • Snort: A popular open-source IDS/IPS system. Requires technical expertise to configure.
   • Suricata: Another powerful open-source option similar to Snort.
4. Regular Security Scans: Identify vulnerabilities in your systems before attackers do.
   • Nessus Essentials: A free vulnerability scanner for home use (limited features).
   • OpenVAS: Another open-source vulnerability scanner.
5. Consider a VPN: A Virtual Private Network encrypts your internet traffic and masks your IP address.
   • Privacy Focus: Choose a reputable VPN provider with a no-logs policy.
   • Performance Impact: VPNs can sometimes slow down your internet connection speed.

Changing Your IP Address – When it Might Help (Temporarily)

If you suspect an active attack, changing your IP address can provide a brief respite while you implement more robust security measures. Here’s how:

• Restart Router: The simplest method for dynamic IPs.
• Contact ISP: Request a new IP address (may not always be possible).
• Disconnect/Reconnect Internet: Often triggers a new IP assignment.

However, remember this is only a temporary solution and should be followed up with the steps outlined above.

cyber security Best Practices

Proactive cyber security measures are far more effective than simply changing your IP address. Keep your software updated, use strong passwords, enable multi-factor authentication where possible, and be cautious of phishing attempts.