Network Troubleshooting Utilities

Ping Command

• Purpose: Check if a device on the network is reachable.
• Protocol Used: ICMP (Internet Control Message Protocol).
• Usage:
  • Commonly used in troubleshooting to see if a device is on the network and responding.
  • Works the same across macOS, Linux, and Windows.
  • Example: ping 1.1.1.1 (Cloudflare DNS)
  • Successful ping sends and receives 64 bytes, showing sequence numbers, TTL (Time to Live), and round trip time.
  • Errors: Displays a timeout message if the device is unreachable.
• Stopping Continuous Ping: Use CTRL + C to stop and see statistics.

Traceroute Command

• Purpose: Maps the route and identifies routers between your device and a destination.
• Operating System Differences:
  • Linux/macOS: traceroute
  • Windows: tracert
• ICMP Usage: Uses ICMP Time to Live exceeded error message; TTL refers to number of hops, not time.
• Challenges: ICMP messages can be filtered by firewalls, shown as asterisks in output.
• Example: Tracing a route to Google DNS 8.8.8.8.
• Output: Shows each hop (router) and response times.

DNS Lookup Tools

• NSLookup:
  • Deprecated but included in Windows, Linux, MacOS.
  • Usage: Perform queries to a DNS server.
• Dig:
  • Preferred over NSLookup.
  • Included in Linux, MacOS, and available for Windows.
  • Provides queries and responses in a different format but similar information.
• Example Query: www.professormesser.com returns multiple IPs for redundancy.

Packet Capture Tools

• TCPDump:
  • Command-line packet capture utility available in Linux/macOS.
  • Saves captures in PCAP format, compatible with Wireshark.
  • Filters can be used to limit data and save to files for later analysis.
• Windows Equivalent: WinDump.

Network Statistics Tool

• Netstat:
  • Shows active connections and their executables.
  • Options include:
    • netstat -a: All active connections.
    • netstat -b: Show executables in Windows.
    • netstat -n: Display only IP addresses.
• Usage: Identifying ports and processes that are open and communicating.

IP Configuration Tools

• IPConfig (Windows):
  • Displays IP, subnet mask, and default gateway.
  • Use /all for detailed information like MAC address.
• IfConfig (Linux/macOS):
  • Provides similar information as IPConfig.
  • Newer command: ip address.

Address Resolution Protocol (ARP)

• ARP Table: Maps IP addresses to MAC addresses.
• View ARP Cache: arp -a
• Usage: Helpful in identifying devices on the local subnet and verifying network connections.