Network Troubleshooting

ping

• Packet Internet Groper
• Used to verify that TCP/IP is:
  • Installed
  • Bound to NIC
  • Configured correctly
  • Communicating with the network
• Sends out a signal called an echo request to another device
  • Other device responds with an echo reply
• ICMP
  • Internet Control Message Protocol
  • Protocol used by echo request/reply
  • Carries error messages and info about the network
• For IPv6
  • ping6 on Linux
  • ping -6 on Windows

ipconfig (Windows)

• Shows current TCP/IP addressing and domain name info
• ipconfig /all shows complete summary

ifconfig (Linux)

• Utility to view/manage TCP/IP settings

nslookup

• Name space lookup
• Allows you to query DNS database from any computer on a network
  • Used to find host name of a device by specifying its IP address (or vice versa)
  • Useful for verifying a host is configured correctly
  • Useful for troubleshooting DNS resolution problems
• Reverse DNS lookup
  • Find host name of device whose IP address you know

dig (Linux)

• Domain Information Groper
• Provides more detailed information than nslookup
• Uses more reliable sources of info to output its results

netstat

• Displays TCP/IP stats and details about TCP/IP components/connections on a host
• Information that can be obtained:
  • Port on which TCP/IP service is running
  • Which network connections are currently established for client
  • How many messages have been handled by a network interface since activated
  • How many data errors have occurred on a particular network interface

tracert (Windows)

• Uses ICMP echo requests to trace path from one networked node to another
• Identifying all intermediate hops between nodes
• Employs trail/error approach to discover nodes at each hop from source --> destination

traceroute (Linux, Unix)

• Uses UDP messages to a random port on destination node (same concept as tracert)
• Employs trail/error approach to discover nodes at each hop from source --> destination

Computer Science Networking