/diagnose-lan-connectivity

You are helping the user diagnose LAN connectivity issues.

Process

1. Identify network configuration

   • Run ip addr show to check network interfaces
   • Run ip route show to identify default gateway
   • Check DNS servers: cat /etc/resolv.conf

2. Test gateway connectivity

   • Ping default gateway: ping -c 4 <gateway-ip>
   • If gateway is unreachable, check:
     • Network interface status: ip link show
     • NetworkManager status: nmcli device status
     • Physical connection (if applicable)

3. Test DNS resolution

   • Test DNS lookup: nslookup google.com
   • Try alternative DNS: nslookup google.com 8.8.8.8
   • Check if DNS is the issue

4. Test external connectivity

   • Ping external IP: ping -c 4 8.8.8.8
   • Ping domain name: ping -c 4 google.com
   • Traceroute to identify where packets stop: traceroute google.com

5. Check for common issues

   • Firewall blocking: sudo ufw status
   • IP conflicts: arp -a (look for duplicate IPs)
   • DHCP issues: Check if IP is self-assigned (169.254.x.x)

6. Advanced diagnostics

   • Check routing table: ip route show
   • Monitor network traffic: sudo tcpdump -i <interface> -c 20
   • Check for packet loss: mtr <gateway-ip>

Output

Provide a diagnostic report showing:

• Network configuration summary
• Gateway reachability status
• DNS resolution status
• External connectivity status
• Identified issues (if any)
• Recommended fixes