Network Troubleshooting Guide

Systematic approach to diagnosing and resolving network issues

Troubleshooting Methodology

1. Define the Problem

  • What exactly is not working?
  • When did the problem start?
  • What changed recently?
  • Is it affecting one device or multiple?

2. Gather Information

  • Network topology and configuration
  • Error messages and logs
  • Current network status
  • Recent changes or updates

3. Follow OSI Model

Work systematically through the layers:

  1. Physical: Cables, power, LEDs
  2. Data Link: Switch ports, MAC addresses
  3. Network: IP configuration, routing
  4. Transport: TCP/UDP connectivity
  5. Application: Service-specific issues

Common IoT Network Issues

Device Cannot Obtain IP Address

Symptoms:

  • Device shows "connecting" but never gets IP
  • DHCP timeout errors
  • IP address shows as 0.0.0.0 or 169.254.x.x

Diagnosis Steps:

  1. Check DHCP server status and available addresses
  2. Verify network credentials (Wi-Fi password)
  3. Check MAC address filtering
  4. Test with static IP configuration
  5. Analyze DHCP traffic with Wireshark

Common Solutions:

  • Restart DHCP server or expand address pool
  • Add device MAC to allowed list
  • Configure static IP as temporary workaround
  • Check for duplicate DHCP servers on network

Intermittent Connectivity

Symptoms:

  • Connection drops randomly
  • High packet loss
  • Timeouts during data transfer

Diagnosis Steps:

  1. Monitor signal strength (Wi-Fi)
  2. Check for interference sources
  3. Analyze packet loss patterns
  4. Test with different network channels
  5. Monitor power supply stability

DNS Resolution Failures

Symptoms:

  • Can ping IP addresses but not domain names
  • "Host not found" errors
  • Web services fail to connect

Diagnosis Steps:

  1. Test DNS servers: nslookup google.com 8.8.8.8
  2. Check DNS configuration on device
  3. Try alternative DNS servers
  4. Verify firewall rules for DNS traffic

Essential Troubleshooting Tools

Wireshark

Use for: Protocol analysis, packet capture, traffic patterns

Key Filters:

  • dhcp - DHCP traffic
  • arp - ARP requests/replies
  • icmp - Ping and error messages
  • tcp.flags.syn==1 - Connection attempts

nmap

Use for: Network discovery, port scanning, service detection

Common Commands:

  • nmap -sn 192.168.1.0/24 - Host discovery
  • nmap -p- target - Full port scan
  • nmap -sV target - Service versions

iperf3

Use for: Bandwidth testing, network performance

Basic Usage:

  • Server: iperf3 -s
  • Client: iperf3 -c server-ip
  • UDP test: iperf3 -c server-ip -u

Pre-Deployment Checklist

Network Configuration

  • □ DHCP reservation configured for critical devices
  • □ Static IP addresses documented
  • □ DNS servers configured with fallbacks
  • □ NTP servers accessible for time synchronization
  • □ Firewall rules tested and documented

Device Configuration

  • □ Network credentials securely stored
  • □ Connection timeout values appropriate
  • □ Retry mechanisms implemented
  • □ Error handling and logging enabled
  • □ Over-the-air update mechanism tested

Monitoring and Maintenance

  • □ Network monitoring tools deployed
  • □ Alert thresholds configured
  • □ Backup connectivity options available
  • □ Remote access methods established
  • □ Documentation and runbooks created