21. Network Troubleshooting

Certifiers

Tests a cable to ensure that it can handle its rated amount of capacity. A certifier can pick up an impedance mismatch as well

What is Step 1 of the CompTIA troubleshooting process?

1. Identify the problem

What is the CompTIA troubleshooting process?

1. Identify the problem - Gather information - Duplicate the problem, if possible - Question users - Identify symptoms - Determine if anything has changed - Approach multiple problems individually 2. Establish a theory of probable cause - Question the obvious - Consider multiple approaches: - Top-to-bottom/bottom-to-top OSI model - Divide and conquer 3. Test the theory to determine the cause - Once the theory is confirmed, determine the next steps to resolve the problem - If the theory is not confirmed, reestablish a new theory or escalate 4. Establish a plan of action to resolve the problem and identify potential effects 5. Implement the solution or escalate as necessary 6. Verify full system functionality and, if applicable, implement preventative measures 7. Document findings, actions, and outcomes

What is Step 2 of the CompTIA troubleshooting process?

2. Establish a theory of probable cause

What is Step 3 of the CompTIA troubleshooting process?

3. Test the theory to determine the cause

What is Step 4 of the CompTIA troubleshooting process?

4. Establish a plan of action to resolve the problem and identify potential effects

What is Step 5 of the CompTIA troubleshooting process?

5. Implement the solution or escalate as necessary

What is Step 6 of the CompTIA troubleshooting process?

6. Verify full system functionality and, if applicable, implement preventative measures

What is Step 7 of the CompTIA troubleshooting process?

7. Document findings, actions, and outcomes

Path MTU Discovery (PMTU)

A method for determining the best MTU setting that works by adding a new feature called the "Don't Fragment (DF) flag" to the IP packet

MTU Black Hole

A problem that occurs when a router receives a message that is too large for the next segment's MTU. The router returns an ICMP error message to the sender, but the error message is not returned correctly. From the sender's perspective, messages are lost for no apparent reason.

Tone Generator

A small electronic device that issues a signal on a wire pair. When used in conjunction with a tone probe, it can help locate the termination of a wire pair

Punchdown Tool

A tool used to punch individual wires from a network cable into their slots to terminate the cable

Cable Stripper

A tool used to strip the sheathing from copper cabling. Device that enables the creation of UTP cables

Tone Probe

A two-part kit that is used to find cables in the walls of a building. Also called a toner probe

NIC Teaming

A type of link aggregation in which two or more NICs work in tandem to handle traffic to and from a single node

While you are asking the user problem-isolating questions, what else should you be doing? A. Asking yourself if there is anything on your side of the network that could be causing the problem. B. Nothing; just keep asking the user questions. C. Using an accusatory tone with the user. D. Playing solitaire.

A. Asking yourself if there is anything on your side of the network that could be causing the problem

What are tone probes and tone generators used for? A. Locating a particular cable B. Testing the dial tone on a PBX system C. A long-duration ping test D. As safety equipment when working in crawl spaces

A. Locating a particular cable

Link Aggregation

As defined by the IEEE 802.3ad standard, link aggregation allows multiple physical connections to be logically bundled into a single logical connection

When trying to establish symptoms over the phone, what kind of questions should you ask of a novice or confused user? A. You should ask open-ended questions and let the user explain the problem in his or her own words. B. You should ask detailed, close-ended questions to try and narrow down the possible causes. C. Leading questions are your best choice for pointing the user in the right direction. D. None; ask the user to bring the machine in because it is useless to troubleshoot over the phone.

A. You should ask open-ended questions and let the user explain the problem in his or her own words

What does nslookup do? A. Retrieves the name space for the network B. Queries DNS for the IP address of the supplied host name C. Performs a reverse IP lookup D. Lists the current running network services on localhost

B. Queries DNS for the IP address of the supplied host name

What is the last step in the troubleshooting process? A. Implementing the solution B. Testing the solution C. Documenting the solution D. Closing the help ticket

C. Documenting the solution

When should you use a cable tester to troubleshoot a network cable? A. When you have a host experiencing a very slow connection B. When you have an intermittent connection problem C. When you have a dead connection and you suspect a broken cable D. When you are trying to find the correct cable up in the plenum

C. When you have a dead connection and you suspect a broken cable

Which command shows you detailed IP information, including DNS server addresses and MAC addresses? A. ipconfig B. ipconfig -a C. ipconfig /all D. ipconfig /dns

C. ipconfig /all

Switching Loop

Connecting and configuring multiple switches together in such a way that causes a circular path to appear

What is Wireshark? A. Protocol analyzer B. Packet sniffer C. Packet analyzer D. All of the above

D. All of the above

One of your users calls you with a complaint that he can't reach the site www.google.com. You try and access the site and discover you can't connect either but you can ping the site with its IP address. What is the most probable culprit? A. The workgroup switch is down. B. Google is down. C. The gateway is down. D. The DNS server is down.

D. The DNS server is down.

What will the command route print return on a Windows system? A. The results of the last tracert B. The gateway's router table C. The routes taken by a concurrent connection D. The current system's route table

D. The current system's route table

Time Domain Reflectometer (TDR)

Detects the location of a fault in a copper cable by sending an electric signal down the copper cable and measuring the time required for the signal to bounce back from the cable fault. A TDM can then mathematically calculate the location of the fault

Optical Time Domain Reflectometer (OTDR)

Detects the location of a fault in a fiber cable by sending light down the fiber-optic cable and measuring the time required for the light to bounce back from the cable fault. The OTDM can then mathematically calculate the location of the fault

Optical Power Meter/Light Meter

Device that measures light intensity of light pulses within or at the terminal ends of fiber-optic cables. To measure the amount of light loss

End-to-End Principle

Early network concept that originally meant that applications and work should happen only at the endpoints in a network, such as in a single client and a single server

Link Aggregation Control Protocol (LACP)

IEEE specification of certain features and options to automate the negotiation, management, load balancing, and failure modes of aggregated ports

Crosstalk

Occurs when the signals of one wire affect the signals on an adjacent wire

Loopback Adapter

Plugs into a port and crosses over the transmit line to the receive line so that outgoing signals can be redirected into the computer for testing

Active Ports

Ports that want to use LACP and send special frames out trying to initiate creating an aggregated logical port

Looking Glass Sites

Remote servers accessible with a browser that contain common collections of diagnostic tools such as ping and traceroute, plus some Border Gateway Protocol (BGP) query tools

Noise

Spurious signals usually caused by faulty hardware or poorly crimped jacks

Multimeters

Test voltage (both AC and DC), resistance, and continuity

Proxy ARP

The process of making remotely connected computers truly act as though they are on the same LAN as local computers

Broadcast Storm

The result of one or more devices sending a nonstop flurry of broadcast frames on the network

MTU Mismatch

The situation when your network's packets are so large that they must be fragmented to fit into your ISP's packets

Voltage Quality Recorder

Tracks voltage over time by plugging into a power outlet

Crimper

Used to attach a connector (for example, an RJ-45 connector) to the end of an unshielded twisted-pair (UTP) cable

Cable Testers

Used to check if there is a continuity problem or if a wire map isn't correct

Passive Ports

Wait for active ports to initiate the conversation before they will respond