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Troubleshooting Questions

April 30th, 2017 Go to comments

Question 1

Explanation

At the end of each frame there is a Frame Check Sequence (FCS) field. FCS can be analyzed to determine if errors have occurred. FCS uses cyclic redundancy check (CRC) algorithm to detect errors in the transmitted frames. Before sending data, the sending host generates a CRC based on the header and data of that frame. When this frame arrives, the receiving host uses the same algorithm to generate its own CRC and compare them. If they do not match then a CRC error will occur. CRC errors (and input errors in general) are often caused by duplex mismatch or Physical layer issues (like faulty cable, faulty network interface card or excessive interference during the transmission,…).

On an Ethernet connection, a duplex mismatch is a condition where two connected devices operate in different duplex modes, that is, one operates in half duplex while the other one operates in full duplex.

Note:
+ Runts are frames which do not meet the minimum frame size of 64 bytes. Runts are usually created by collisions.
+ Giants: frames that are larger than 1,518 bytes

Question 2

Explanation

The ports on the switch are not up indicating it is a layer 1 (physical) problem so we should check cable type, power and how they are plugged in.

Question 3

Question 4

Question 5

Question 6

Explanation

The “show ip nat statistics” only gives us information about NAT translation. We cannot know if IP routing is enabled or the VLANs are up not not.

The “show ip statistics” command does not exist.

In the Troubleshoot part of “How to configure InterVLAN Routing on Layer 3 switches” (http://www.cisco.com/c/en/us/support/docs/lan-switching/inter-vlan-routing/41860-howto-L3-intervlanrouting.html) Cisco recommends to use the “show ip interface brief” command as follows:
Also verify the interface VLAN status by issuing the show ip interface brief command.
+ If the interface status is administratively down, enter the no shutdown command in the VLAN interface configuration mode.
+ If the interface status is down/down, verify the VTP configuration and that the VLANs have been added to the VLAN database. Check to see if a port is assigned to the VLAN and whether it is in the Spanning Tree forwarding state.

Initiate a ping from an end device in one VLAN to the interface VLAN on another VLAN in order to verify that the switch routes between VLANs. In this example, ping from VLAN 2 (10.1.2.1) to Interface VLAN 3 (10.1.3.1) or Interface VLAN 10 (10.1.10.1). If the ping fails, verify that IP routing is enabled and that the VLAN interfaces status is up with the show ip interface brief command.

Also in the above link Cisco only mentions about the “show ip route” in the “Verify” part, not “Troubleshooting” part so “show ip interface brief” is a better answer.

Question 7

Explanation

In fact all three of the above answers are in the problem-solving process but “gather facts” is at Step 2 while “Create an action plan” and “Implement an action plan” is at step 4 & 5 of this link http://www.cisco.com/en/US/docs/internetworking/troubleshooting/guide/tr1901.html

Step 2 Gather the facts that you need to help isolate possible causes.
Ask questions of affected users, network administrators, managers, and other key people. Collect information from sources such as network management systems, protocol analyzer traces, output from router diagnostic commands, or software release notes.

Question 8

Explanation

The “show interfaces …” command gives us information about speed and duplex mode of the interface. In the output below, the link speed is 100Mbps and it is working in Full-duplex mode.

show_interfaces_fa0_0.jpg

Question 9

Question 10

Explanation

To check the connectivity between a host and a destination (through some networks) we can use both “tracert” and “ping” commands. But the difference between these two commands is the “tracert” command can display a list of near-side router interfaces in the path between the source and the destination. In this question the PC and the host are in the same VLAN so “tracert” command is not useful as there is no router to go through. Therefore the best answer in this case is “ping address”.

Note: “traceroute” command has the same function of the “tracert” command but it is used on Cisco routers only, not on a PC.

Question 11

Explanation

Complete these steps to troubleshoot this problem:
Ensure the router can reach the DNS server. Ping the DNS server from the router using its IP address, and make sure that the ip name-server command is used to configure the IP address of the DNS server on the router.

Reference: https://www.cisco.com/c/en/us/support/docs/ip/domain-name-system-dns/24182-reversedns.html

Question 12

Explanation

The extended traceroute command can be used by typing only “traceroute” keyword on the device as follows:

extended_traceroute.jpg

We can specify a source address (which can be a specific IP address or interface on that device). We can also specify a Time to Live value of each packet sent.

Question 13

Explanation

A late collision is defined as any collision that occurs after the first 512 bits of the frame have been transmitted. The usual possible causes are full-duplex/half-duplex mismatch, exceeded Ethernet cable length limits, or defective hardware such as incorrect cabling, non-compliant number of hubs in the network, or a bad NIC.

Note: On an Ethernet connection, a duplex mismatch is a condition where two connected devices operate in different duplex modes, that is, one operates in half duplex while the other one operates in full duplex.

Duplex mismatch would not cause the link to be down/down, but would only result in poor performance like increase late collisions on the interface.

Question 14

Explanation

From this paragraph:

Step 2. Resolve or escalate: Problem isolation should eventually uncover the root cause of the problem – that is, the cause which, if fixed, will resolve the problem. In short, resolving the problem means finding the root cause of the problem and fixing that problem. Of course, what do you do if you cannot find the root cause, or fix (resolve) that root cause once found? Escalate the problem. Most companies have a defined escalation process, with different levels of technical support and management support depending on whether the next step requires more technical expertise or management decision making.

Reference: ICND1 100-105 Official Cert Guide

Also from this link: http://www.ciscopress.com/articles/article.asp?p=1578504&seqNum=2

“After you have clearly defined the problem, you have one more step to take before starting the actual troubleshooting process. You must determine whether this problem is your responsibility or if it needs to be escalated to another department or person. For example, assume the reported problem is this: “When user Y tries to access the corporate directory on the company intranet, she gets a message that says permission is denied. She can access all other intranet pages.” You are a network engineer, and you do not have access to the servers. A separate department in your company manages the intranet servers. Therefore, you must know what to do when this type of problem is reported to you as a network problem. You must know whether to start troubleshooting or to escalate it to the server department. It is important that you know which type of problems is your responsibility to act on, what minimal actions you need to take before you escalate a problem, and how you escalate a problem.”

So we can say answer A is the most suitable choice.

Comments (21) Comments
  1. anonymous
    February 19th, 2017

    for Question 1 I’ve seen many other places give the answer of “late collisions”, such as here http://vceguide.com/which-interface-counter-can-you-use-to-diagnose-a-duplex-mismatch-problem/

    Can you confirm the right answer?

  2. Sisi
    February 23rd, 2017

    For Question 6:

    “Initiate a ping from an end device in one VLAN to the interface VLAN on another VLAN in order to verify that the switch routes between VLANs. In this example, ping from VLAN 2 (10.1.2.1) to Interface VLAN 3 (10.1.3.1) or Interface VLAN 10 (10.1.10.1). If the ping fails, verify that IP routing is enabled and that the VLAN interfaces status is up with the show ip interface brief command.”

    http://www.cisco.com/c/en/us/support/docs/lan-switching/inter-vlan-routing/41860-howto-L3-intervlanrouting.html

    So the correct answer would be A

  3. @theunreal
    March 4th, 2017

    @anonymous: I wa thinkin the same, but checking directly from Cisco ICDN2 material they gave me during the class: I can read that both input errors (CRC errors) and output errors (late collision) usually indicate a duplex mismatch issue, so I think that both arecorrect. But I don’t know if at the exam can exist a single-answer question with more that one correct option.

  4. real name
    March 13th, 2017

    i see no questions… only explanations

  5. LKB
    May 25th, 2017

    I don’t see any questions. Please help?

  6. Anonymous
    June 1st, 2017

    Describe the best way to troubleshoot and isolate a network problem?
    A. Create an action plan
    B. Implement an action plan
    C. Gather facts
    D. others

    what is the correct answer of this question?
    B or C?

  7. Error
    June 8th, 2017

    @9tut correct question 10, you are saying that the correct answer is ping address but you have A as an answer

  8. Francesco
    June 20th, 2017
  9. Washaz
    July 11th, 2017

    @9tut, the answer to quest 10 is ping, you have a good explanation, but your answer is marked as tracert (A).

  10. Hello 9tut
    July 24th, 2017

    It is stated in Q11 that the issue is dns, so it should it be E and not C.

  11. MKH_TX
    July 31st, 2017

    Question 14

    When is the most appropriate time to escalate an issue that you troubleshooting?
    the correct answer should be C. When you have gathered all information about an issue.
    Not A.

  12. komj
    August 19th, 2017

    @MKH_TX
    I also think that answer to question 14 is C since statement A should be implied if the issue escalation is going to happen…

  13. soiree
    August 23rd, 2017

    Hi to All there!
    I like to read so many point of view how to troubleshoot a Campus Network of 65 Buildings. For example, your manager call you and tell that all the Network of the Campus is down(65 buildings). How to fix these are kind of

    Soiree

  14. m1987
    September 22nd, 2017

    Q11
    The answer should be B and D
    “Ping the DNS server from the router using its IP address,
    Make sure that the ip name-server command is used to configure the IP address of the DNS server on the router.”

  15. m1987
    September 22nd, 2017

    ops i meant B&E

  16. Question
    October 8th, 2017

    Name Servers are a fundamental part of the Domain Name System (DNS) that allow users to use domains instead of IP addresses.
    Client’s IP can be manually assigned so there is no DHCP involved.
    The correct answers for question 11 should be B and E.

  17. Anonymous
    October 20th, 2017

    Hi guys,
    I have CCNA (200-125) exam in the next week.
    Can anyone help me with the latest dumps for CCNA (200-125).

  18. Anonymous
    October 28th, 2017

    Just go for the latest valid version from this site https://www.examgood.com/200-125.html

  19. eltaib
    November 8th, 2017

    this question (When is the most appropriate time to escalate an issue that you troubleshooting? )
    what is correct A or C

  20. eltaib
    November 8th, 2017

    This question came in today’s exam and I have chosen c

  21. noney12
    November 17th, 2017

    answers for question 1 and 13 contradict each other

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