Network Troubleshooting and Tools (5) Flashcards
Ed is working the help desk at a local computer store, and he receives a call from a customer trying to set up a home network using Windows 10 and wired Ethernet equipment. The customer reports that, from her computer, she can see the two other computers in the house, but she cannot access the Internet. Ed asks her to run the ipconfig /all command and read the results to him. She says that her IP address is 172.16.41.2, her subnet mask is 255.255.255.0, and her default gateway is 172.16.43.1. Which of the following is most likely the cause of the customer’s problem?
The customer’s network cable is unplugged.
The customer has an incorrect subnet mask.
The customer has an incorrect default gateway address.
The customer has an incorrect default gateway address.
Because the customer can access the other two computers in the house, Ed knows that her IP address and subnet mask are properly configured that the network cable is plugged in and functional. Ed also knows that the computer’s DNS record does not play a role in outgoing connections. The problem is most likely the default gateway because the gateway address the customer specified is on another network, 172.16.43.0, rather than on her own network, 172.16.41.0
Alice is attempting to troubleshoot a communication problem between two hosts on the same network. She decides to use a protocol analyzer to capture traffic on the network. After finishing the capture, Alice notices that there are over 15,000 frames in the protocol analyzer’s capture buffer. She is having a difficult time identifying the frames that relate to the problem because there are so many in the buffer. She wants to eliminate the extraneous frames from her view, enabling her to view only the frames transmitted by these two hosts. What does Alice have to do to accomplish this?
Configure a display filter.
Configure a capture filter.
Delete the extraneous frames from the buffer.
Configure a display filter.
Once the frames are in the buffer, Alice can configure a display filter to block the unwanted frames from view. This does not delete them from the buffer. Since the capture was already performed, there is no need to restart the capture. Configuring a capture filter will not meet the requirements, because the filter will eliminate the other frames completely from the buffer. It is not possible to delete frames from an analyzer buffer
Ed is working the help desk at a local computer store, and he receives a call from a customer trying to set up a home network using Windows 10 and wired Ethernet equipment. The customer reports that she cannot access the other two computers in the house, nor can she access the Internet. Ed asks her to run the ipconfig /all command and read the results to him. She says that her IP address is 192.168.0.2, her subnet mask is 255.255.255.0, and her default gateway is 192.168.0.1. Which of the following is most likely the cause of the customer’s problem?
The customer’s network cable is unplugged.
The customer’s network address cannot include a zero.
The customer has an incorrect subnet mask.
The customer’s network cable is unplugged.
The customer’s IP address, subnet mask, and default gateway are appropriate for her home network. There is nothing wrong with having a zero in the network address. Therefore, of the options presented, the only logical choice is that the network cable is unplugged
Ralph is testing a twisted pair cable run using a tone generator and locator. When he applies the tone generator to one particular wire at one end of the cable, he fails to detect a tone at the other end. Which of the following faults has Ralph discovered?
Open
Short
Split pair
Open
The failure to detect a tone on a wire indicates that there is either a break in the wire somewhere inside the cable or a bad connection with the pin in one or both connectors. This condition is called an open circuit. A short is when a wire is connected to two or more pins at one end of the cable. A split pair is a connection in which two wires are incorrectly mapped in exactly the same way on both ends of the cable. Crosstalk is a type of interference caused by signals on one wire bleeding over to other wires
Ed is working the help desk at a local computer store, and he receives a call from a customer trying to set up a home network using Windows 10 and wired Ethernet equipment. The customer reports that, from her computer, she cannot access the two other computers in the house, nor can she access the Internet. Ed asks her to run the ipconfig /all command and read the results to him. She says that her IP address is 172.16.41.2, her subnet mask is 255.255.255.0, and her default gateway is 172.16.43.1. Which of the following could conceivably be the cause of the customer’s problem? (Choose all correct answers.)
The customer has an incorrect IP address.
The customer has an incorrect subnet mask.
The customer has an incorrect default gateway address.
The computer’s DNS record contains the wrong information.
The customer has an incorrect subnet mask.
The customer has an incorrect default gateway address.
The computer could have an incorrect subnet mask or an incorrect default gateway address. Because the customer’s computer has an IP address on the 172.16.41.0/24 network, her default gateway address should also be on that network. However, if the subnet mask value is incorrect and should be 255.255.0.0, then the default gateway address is correct
Ralph is testing a twisted pair cable run using a tone generator and locator. When he applies the tone generator to a particular pin at one end of the cable, he detects a tone on two pins at the other end. Which of the following faults has Ralph discovered?
Open
Short
Split pair
Short
A short is when a wire is connected to two or more pins at one end of the cable or when the conductors of two or more wires are touching inside the cable. This would cause a tone applied to a single pin at one end to be heard on multiple pins at the other end. An open circuit would manifest as a failure to detect a tone on a wire, indicating that there is either a break in the wire somewhere inside the cable or a bad connection with the pin in one or both connectors. A split pair is a connection in which two wires are incorrectly mapped in exactly the same way on both ends of the cable. Crosstalk is a type of interference caused by signals on one wire bleeding over to other wires
Ralph is using a tone generator and locator to test some newly installed twisted pair cable runs on his network. Which of the following cable faults will he be unable to detect?
Open
Short
Split pair
Split pair
A split pair is a connection in which two wires are incorrectly mapped in exactly the same way on both ends of the cable. Each pin on one end of the cable is correctly wired to the corresponding pin at the other end, but the wires inside the cable used to make the connections are incorrect. In a properly wired connection, each twisted pair should contain a signal and a ground wire. In a split pair, you can have two signal wires twisted together as a pair. This can generate excessive amounts of crosstalk, corrupting both of the signals involved. Because all of the pins are connected properly, a tone generator and locator cannot detect this fault. An open circuit would manifest as a failure to detect a tone on a wire, indicating that there is either a break in the wire somewhere inside the cable or a bad connection with the pin in one or both connectors. A short is when a wire is connected to two or more pins at one end of the cable or when the conductors of two or more wires are touching inside the cable. Transposed pairs is a fault in which both of the wires in a pair are connected to the wrong pins at one end of the cable. All three of these faults are detectable with a tone generator and locator
Alice has been told by a consultant that the newly installed twisted pair cable runs on her network might have split pairs. Which of the following cable testing tools can she use to detect split pairs?
Wiremap tester
Multimeter
Cable certifier
Cable certifier
A split pair is a connection in which two wires are incorrectly mapped in exactly the same way on both ends of the cable. Each pin on one end of the cable is correctly wired to the corresponding pin at the other end, but the wires inside the cable used to make the connections are incorrect. In a properly wired connection, each twisted pair should contain a signal and a ground wire. In a split pair, you can have two signal wires twisted together as a pair. This can generate excessive amounts of crosstalk, corrupting both of the signals involved. Because all of the pins are connected properly, a tone generator and locator cannot detect this fault, and neither can a wiremap tester or a multimeter. However, a cable certifier is a highly sophisticated electronic device that can detect all types of cable faults, including split pairs, as well as measure cable performance characteristics
Ralph is testing some newly installed twisted pair cable runs on his network using a wiremap tester, and he has found one run that appears to have a cable break. However, the connectors at both ends are correctly installed, so the break must be somewhere inside the cable itself, which is nearly 100 meters long. Which of the following tools can Ralph use to determine the location of the cable break? (Choose all correct answers.)
Tone generator and locator
Multimeter
Time domain reflectometer
Cable certifier
Time domain reflectometer
Cable certifier
A time domain reflectometer (TDR) is a device that determines the length of a cable by transmitting a signal at one end and measuring how long it takes for a reflection of the signal to return from the other end. Using this information and the cable’s nominal velocity of propagation (NVP)—a specification supplied by the cable manufacturer—the device can calculate the length of a cable run. In a cable with a break in its length, a TDR calculates the length of the cable up to the break. Cable certifiers typically have time domain reflectometry capabilities integrated into the unit. A tone generator and locator or a multimeter cannot locate a cable break
Which of the following terms describes a connectivity problem on wired networks that is caused by individual packets that are delayed due to network congestion, different routing, or queuing problems?
Latency
Attenuation
Jitter
Jitter
When individual packets in a data stream are delayed, the resulting connectivity problem is called jitter. Although this condition might not cause problems for asynchronous applications, real-time communications, such as Voice over IP or streaming video, can suffer interruptions, from which the phenomenon gets its name. Latency describes a generalized delay in network transmissions, not individual packet delays. Attenuation is the weakening of a signal as it travels through a network medium. A bottleneck is a condition in which all traffic is delayed, due to a faulty or inadequate component
Which of the following network applications are most likely to be obviously affected by the wired network connectivity problem known as jitter? (Choose all correct answers.)
VoIP
Streaming video
Instant messaging
VoIP
Streaming video
Jitter is a connectivity problem on wired networks that is caused by individual packets that are delayed due to network congestion, different routing, or queuing problems. When individual packets in a data stream are delayed, the resulting connectivity problem is called jitter. While this condition might not cause problems for asynchronous applications, such as email and instant messaging, real-time communications, such as Voice over IP (VoIP) or streaming video, can suffer intermittent interruptions, from which the phenomenon gets its name
Alice’s company has moved to a building that was prewired for Ethernet. However, since installing the company’s Gigabit Ethernet equipment using the existing cable runs, performance has been poor. After performing some packet captures and analyzing the traffic samples, Alice discovers that there are a great many Ethernet frames being retransmitted. Next, she examines the cable runs in the drop ceilings. They do not appear to be overly long, and they do not appear to run near any major sources of electromagnetic interference. Which of the following could be the problem?
Some of the cable runs are using T568A pinouts, and some are using T568B.
The cables have only two wire pairs connected, instead of four.
The existing cable is not rated for use with Gigabit Ethernet.
The existing cable is not rated for use with Gigabit Ethernet.
Of the options provided, the only possible source of the problem is that the cable runs are using a cable type not rated for Gigabit Ethernet. Some older buildings might still have Category 3 cable installed, which was used in the original twisted pair Ethernet specification. Cat 3 is unsuitable for use with Gigabit Ethernet in many ways and can result in the poor performance that Alice is experiencing. A cable installation with runs wired using different pinout standards will not affect performance as long as each run uses the same pinouts at both ends. Gigabit Ethernet will not function at all if only two wire pairs are connected. The transceivers are located in the equipment that Alice company brought from the old location, so they are not mismatched
Ralph is responsible for the network installation in a new building purchased by his company, and he has elected to have Category 6 unshielded twisted pair cable installed. The company president has asked him if it is possible to run their Gigabit Ethernet network using two of the wire pairs in the cable, while using the other two pairs for telephone connections. Ralph is not sure, so he sets up a lab network using cables with only two pairs connected. When he plugs computers into the switch and turns them on, the LEDs labeled 1000 light up, indicating that a Gigabit Ethernet connection has been established. Ralph gets excited at the thought of how much money he might save the company by using the same cable for both telephone and data. However, while the LED is lit, he can’t seem to connect to another system over his test network. Which of the following describes what he must do to correct the problem?
Ralph is using the wrong two wire pairs for the Gigabit Ethernet connection. He must rewire the connectors.
Ralph is using the wrong pinout standard on his lab network. He must use T568A.
Ralph must use all four wire pairs for a Gigabit Ethernet connection.
Ralph must use all four wire pairs for a Gigabit Ethernet connection.
The autonegotiation mechanism is not the problem, nor is the pinout standard or Ralph’s wire pair selection. The speed autonegotiation mechanism in Gigabit Ethernet uses only two wire pairs, so although the LEDs do light up successfully, a functional Gigabit Ethernet data connection requires all four wire pairs
Ed is inspecting the cable runs recently installed for some new Gigabit Ethernet systems on his network. Looking at the patch panel connections, he notices that they are wired using the T568B pinout standard. However, when he examines the wall plate connections, he sees that they are wired using the T568A standard. What is the best way for Ed to resolve the problem?
Call the contractor and have all of the wall plate connectors rewired using the T568B standard.
Configure the switches not to use a crossover circuit for all of the ports connected to the patch panel.
Do nothing. The cable runs will function properly as is.
Do nothing. The cable runs will function properly as is.
Cable runs are traditionally wired “straight through,” that is, with the transmit pins at one end wired to the transmit pins at the other end. It is the switch that is supposed to implement the crossover circuit that connects the transmit pins to the receive pins. Cable runs wired using T568A at one end and T568B at the other end create a crossover circuit in the cable run. At one time, this would have been a serious problem, but today’s switches automatically configure crossover circuits as needed, so they will adjust themselves to adapt to the cable runs. All of the other options would correct the problem, but doing nothing is certainly the best option
Alice has recently installed some new computers onto her Gigabit Ethernet network. To ensure best possible network performance, she has configured the network adapters in the new computers to run at 1 Gbps speed and use full-duplex communication. Once the computers are in service, however, Alice begins getting reports of extremely poor network performance on those machines. She tries running some ping tests and does not see any problem. She calls in a consultant to perform a packet analysis, and the consultant detects large numbers of packet collisions, late collisions, cyclical redundancy check (CRC) errors, and runt frames. Which of the following could be the problem?
Duplex mismatch
TX/RX reversal
Incorrect cable type
Duplex mismatch
There should be no collisions at all on a full-duplex network, so the problem is clearly related to the duplexing of the communications. Ethernet running over twisted pair cable, in its original half-duplex mode, detects collisions by looking for data on the transmit and receive pins at the same time. In full-duplex mode, data is supposed to be transmitted and received at the same time. When one side of a connection is configured to use full duplex, as Alice’s new computers are, and the other end is configured to use half duplex (as the switches must be), the full-duplex communications on the one side look like collisions to the half-duplex side. The half-duplex adapter transmits a jam signal as a result of each collision, which causes the full-duplex side to receive an incomplete frame. Both sides then start to retransmit frames in a continuing cycle, causing network performance to diminish drastically. The ping tests do not detect a problem because ping only transmits a small amount of data in one direction at a time. The other options would likely cause the ping tests to fail as well. The solution to the problem is to configure all of the devices to autonegotiate their speed and duplex modes
