12.8.4 Troubleshooting Tool Facts

What should you check first when troubleshooting physical network issues?

Check link lights on both the workstation and switch.

What does an unlit link light usually indicate?

A physical connection problem.

What is a first step when a cable may be faulty?

Swap the cable.

What is another step when troubleshooting physical connectivity?

Try a different switch port.

What should you verify if a network card is suspected faulty?

Ensure it is properly seated.

What tools can test network cables or NICs?

Loopback plugs and cable testers.

What causes electromagnetic or radio frequency interference?

Nearby electrical devices or wireless devices on similar frequencies.

What should be avoided for wired cable routing?

Running cables near motors or fluorescent lights.

What wireless devices can cause interference?

Microwaves and cordless phones.

What is a sign of interference in a network?

Dropped packets or collisions.

What should you check if devices can communicate locally but not externally?

Default gateway configuration.

What should you verify if a specific service is unreachable?

The service is running and properly configured.

What network configuration issue can prevent connectivity across networks?

Incorrect subnet or routing configuration.

What is latency?

The time it takes data to travel across a network.

What is bandwidth?

The size of the communication channel.

What is throughput?

The amount of data a system can transmit or receive.

What does bandwidth saturation mean?

The network has reached maximum capacity.

What is a network bottleneck?

A point where performance is limited due to overload.

What is RDMA used for?

High-throughput, low-latency communication with minimal CPU usage.

What are IB, iWARP, and RoCE?

RDMA communication standards.

What is a Unix domain socket used for?

Communication between processes on the same host.

Why is localhost communication faster with Unix sockets?

It occurs inside the kernel instead of over the network stack.

What does the ping command test?

Connectivity between network hosts.

What does a failed ping to all hosts indicate?

A local network issue such as NIC or cable problems.

What does a successful local ping but failed external ping suggest?

A default gateway problem.

What does a ping using DNS failure indicate?

Name resolution problem.

What does the -c option in ping do?

Specifies number of ICMP requests sent.

What does netstat display?

Connections, routing table, and interface information.

What does netstat -a show?

All listening and non-listening ports.

What does netstat -r show?

The routing table.

What is replacing netstat?

ip, ss, and related iproute2 tools.

What does nc (netcat) do?

Establishes TCP or UDP connections between hosts.

What is required before using nc between systems?

Open appropriate firewall ports.

What does traceroute show?

The path packets take to a destination.

What is a hop in traceroute?

A router along the path.

What does traceroute RTT measure?

Time for a packet to go to a hop and return.

What does tracepath do?

Similar to traceroute for path discovery.

What is nslookup used for?

Performing DNS lookups.

What is dig used for?

Detailed DNS queries and troubleshooting.

What does ss provide?

Detailed socket and connection statistics.

What does ss -t show?

TCP sockets only.

What does nmcli do?

Manages NetworkManager from the command line.

What is nmtui used for?

Text-based interface for NetworkManager configuration.

What does iftop show?

Real-time bandwidth usage by host pairs.

Why might iftop generate extra traffic?

It performs DNS lookups.

What does iperf measure?

Network throughput performance.

What does tcpdump do?

Captures and analyzes network packets.

What does ipset manage?

Groups of IP addresses for firewall rules.

What does mtr combine?

Ping and traceroute functionality.

What does arp show?

IP-to-MAC address mappings.

What is whois used for?

Looking up domain registration information.

What is Wireshark used for?

GUI-based packet capture and analysis.

What is tshark?

Command-line version of Wireshark.