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Fix ARP Spoofing: Restore Network Traffic

G5 Cyber Security

TL;DR

ARP spoofing can stop you receiving traffic from devices on your local network. This guide shows how to identify and fix it, mainly by clearing your ARP cache and using static ARP entries for important devices.

What is ARP Spoofing?

ARP (Address Resolution Protocol) maps IP addresses to physical MAC addresses. Spoofing tricks your computer into thinking the wrong MAC address belongs to a specific IP, meaning traffic intended for one device goes elsewhere – often an attacker’s machine. This can lead to data theft or denial of service.

How to Identify ARP Spoofing

  1. Symptoms: You might notice you can’t access devices on your network by name (but maybe still by IP address), intermittent connectivity, or slow network speeds.
  2. ARP Cache Inspection: Use the arp -a command to view your ARP cache. Look for duplicate IP addresses with different MAC addresses. This is a strong indicator of spoofing. 
    arp -a
  3. Network Monitoring Tools: Tools like Wireshark can capture network traffic and reveal suspicious ARP requests/replies.

Fixing ARP Spoofing

  1. Clear Your ARP Cache: This is the quickest first step.
    • Windows: Open Command Prompt as administrator and run arp -d *.
    arp -d *
  2. macOS/Linux: Use sudo arp -d for each suspicious IP, or sudo ip neigh flush all to clear the entire cache (be careful with this one!).
    3. sudo arp -d 192.168.1.100
  3. Static ARP Entries: For critical devices (like your router), create static entries to prevent spoofing.
    • Windows: Use the arp -s command. You’ll need to know the correct MAC address of the device. Find this via your router’s admin interface or by temporarily connecting directly to the device and using ipconfig /all (on Windows) or ifconfig (macOS/Linux). 
      arp -s 192.168.1.1 00:1A:2B:3C:4D:5E
    • macOS/Linux: Edit your network configuration file (usually in /etc/network/interfaces or similar, depending on your distribution) and add a static ARP entry. 
      # Example for /etc/network/interfaces
auto eth0
iface eth0 inet static
  address 192.168.1.50
  netmask 255.255.255.0
  gateway 192.168.1.1
  arp 192.168.1.1 00:1A:2B:3C:4D:5E
  4. Router Security: Check your router’s settings for ARP inspection or dynamic ARP protection features and enable them if available. This helps prevent spoofing at the network level.
  5. Firewall: Configure a firewall to block suspicious traffic based on MAC address or IP address.
  6. Switch Security (if applicable): Managed switches often have port security features that can limit which MAC addresses are allowed on each port, preventing attackers from connecting rogue devices.

Preventing Future Attacks

  1. Keep Software Updated: Ensure your operating system and network drivers are up-to-date with the latest security patches.
  2. Be Careful With Public Wi-Fi: Avoid connecting sensitive devices to untrusted public networks.
  3. Strong Passwords: Use strong, unique passwords for your router and any other network devices.
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