5 – Network Troubleshooting

Question 1

What is a TDR?

Answer 1

Time Domain Reflectometer

A tool that provides advanced analysis of network cables.

For copper, it’s a TDR. For fiber, it’s an OTDR.

Question 2

What is an OTDR?

Answer 2

Optical Time Domain Reflectometer

Same thing as a TDR, but for fiber optic cable.

Question 3

What types of things can a TDR be used to identify?

Answer 3

• Frequency testing
• Crosstalk
• Signal loss
• Cable impedance information
• Estimated cable length
• Cut or break locations (estimates how far down the cable that break is located)

Question 4

How does a TDR work?

Answer 4

It sends an electrical pulse down the cable (or, for an OTDR, it sends a light).

Impedance discontinuities cause a reflect, and the TDR calculates time and distance based on that reflection.

Question 5

What is a light meter used for?

Answer 5

It sends a light (either laser or LED) from one side of a fiber optic cable, and measures the light power on the other side, to determine the strength of the signal getting through the cable.

Question 6

What is a Multimeter?

Answer 6

A tool to check either AC or DC voltage.

AC voltage to checke the wall outlet output; DC voltage to check the PC power supply output or CMOS battery power.

Question 7

What is a Spectrum Analyzer?

Answer 7

Measures and displays signals from the full wireless frequency spectrum.

Useful to visually see signal strength, conflicts, and interference.

Question 8

What is DIG?

Answer 8

Domain Information Groper

• Looks up info from DNS servers.
• Replaces nslookup, which is now deprecated.
• More advanced than nslookup.
• Not native to any Windows version, but it can be downloaded and added.

Question 9

What is iptables?

Answer 9

A stateful firewall available for Linux

• One of the more popular of the many firewall options for Linux’
• Provides stateful filtering of traffic in the kernel of the Linux OS
• Usually placed on a device or server to filter traffic to and from the device
• Can also serve as a firewall at the edge of a network to filter the entire network

Question 10

What is netstat?

Answer 10

A command line tool for Network Statistics, available on many different OSs, including Windows, Linux, and Unix.

Question 11

What is tcpdump?

Answer 11

A command line tool to capture packets

• Available in most Unix/Linux OSs
• included in MacOs, can be downloaded for Windows (it’s called WinDump)

You can:

• apply filters
• view in real-time
• save the data and use in another application

Question 12

What is a pcap file?

Answer 12

A file format that is easily readable by many protocol analyzer applications. It contains tcpdump data, or similar.

Question 13

What is pathping?

Answer 13

It combines ping and traceroute and adds some additional functions.

This command provides details of the path between two hosts, and Ping-like statistics for each node in the path based on samples taken over a time period.

It is included in Windows NT and later.

Question 14

What is nmap?

Answer 14

Network Mapper

A Linux CLI tool

Question 15

What is arp?

Answer 15

CLI windows more info…

Question 16

In Networking, what does “attenuation” refer to?

Answer 16

Attenuation is the lose of intensity as a signal moves through a medium.

Signal strength diminishes / degrades over distance. This degradation is called attenuation.

Question 17

What is jitter?

Answer 17

Jitter is a delays between frames.

Data should arrive at regular intervals.

This is most problematic for real-time applications, because if you miss a packet, there’s no retransmission.

Question 18

What is an open circuit?

Answer 18

A break in a connection.

Often, a broken cable.