Network Troubleshooting Tools and Commands

Ping Command

• Purpose: Test reachability of devices on a network
• Protocol Used: ICMP (Internet Control Message Protocol)
• Key Features:
  • Shows round-trip time
  • Indicates if another device is responding
  • Default Windows ping: 4 pings
  • Displays data size and time to live (TTL)
• Example: ping 9.9.9.9 to test connectivity to a DNS provider
• Output Details: Number of pings sent/received, round-trip times (min, max, avg)
• Usage: First tool to use in troubleshooting network issues

IP Configuration Commands

• Windows: ipconfig
  • Shows DNS name, IP address, subnet mask, default gateway
  • ipconfig /all for detailed information
• Linux: ifconfig or ip address (newer versions)

DNS Query Commands

• nslookup: Available on Windows, Linux, etc.
  • Retrieves canonical names, IP addresses, cache timers
  • Example: nslookup www.professormesser.com
• dig: More straightforward, not included with Windows by default
  • Example: dig www.professormesser.com

Traceroute Command

• Purpose: Trace the route packets take from source to destination
• Windows: tracert
• Linux/MacOS: traceroute
• How It Works: Uses TTL field in ICMP packets to map the route
• Example: tracert 9.9.9.9
• Details: Shows each hop and associated IP address or URL

ARP Command

• Purpose: Resolve IP addresses to MAC addresses
• Command: arp -a
• Example: arp -a to view the ARP cache
• Usage: Verify if a device is responding on the local network

Netstat Command

• Purpose: Network statistics and active connections
• Commands:
  • netstat -a: All connections
  • netstat -b: Executable involved in network connections (Windows)
  • netstat -n: Shows IP addresses instead of domain names
• Example: netstat -n to see active connections

Hostname Command

• Purpose: Display the name of the current host
• Usage: Ensure commands are run on the correct system
• Example: hostname

Route Print Command

• Purpose: Display the routing table
• Windows: route print
• Linux/MacOS: netstat -r
• Example: route print to view IPv4 routing table

Telnet Command

• Purpose: Terminal access to remote devices (insecure, use SSH for secure access)
• Common Port: TCP 23
• Usage: Check if a port is open/responding
• Example: telnet 10.1.10.222 5000

Tcpdump Command

• Purpose: Capture and analyze network packets
• Availability: Unix, Linux, MacOS, some Windows versions (WinDump)
• Usage: Apply filters for real-time data, save in pcap format for analysis
• Example: Basic tcpdump output shows timestamps, protocols, source, and destination

Nmap Command

• Purpose: Network mapping and scanning
• Capabilities:
  • Identify open ports
  • Determine operating systems
  • Perform service scans
• Example: nmap -f 10.1.10.222 for a fast scan

Common Platform Commands

• show interface: Display interface details (Cisco: show interfaces status)
• show config: Show configuration (Cisco: show run for running configuration)
• show route: Display routing table (Cisco: show ip route)
• Usage: Commands are similar across different devices and manufacturers