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ICND2 – Troubleshooting Questions

October 4th, 2017 in ICND2 200-105 Go to comments

Question 1


Below is an example of the output of this command:


The “show controllers serial …” command tells us about the type of the cable (in the case V.35 DTE cable) and the status of the physical layer of the interface. In above output we learn that there is an cable attached on S0/0 interface. If no cable is found we will see the line “No DTE cable” instead.

Question 2

Question 3


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.

With the “show ip interface brief” we can see if the interface VLANs are up or not but cannot see if IP routing is enabled or not. So let’s see what information can be learned with the “show ip route” command.

By using the command “show ip route” we will learn if IP routing is enabled. If it is not enabled we will see this output:


After enabling ip routing (via the “ip routing” in global configuration mode) we can see all the interfaces. For example:


If we shut down an interface VLAN (Vlan18)

Sw1(config)#interface vlan 18

then we will not see it in the routing table any more.


Therefore if the statement “local VLANs are up” means “the interface VLANs are up” then the “show ip route” is the best answer in this case.

Note: The IOS used to test is IOSv15.1

Question 4


To check the connectivity between a host and a destination (through some networks) we can use both “tracert” and “traceroute” 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. The “traceroute” command has the same function of the “tracert” command but it is used on Cisco routers only, not on a PC -> B is correct.

Question 5


Answer B is not correct because “debug access-list ” command does not exist.

The reason answer E is correct because this command can help us see if the access-list was applied to the correct interface or not.

Question 6


The subnet of Fa0/0 of R2 is (range from to which covers the subnet of S0/1 interface so in fact the answer C is not correct. But from the output of the “show ip interface brief” command we see both Fa0/0 and S0/1 interfaces’ statuses are ‘up/up’ -> they are working normally. So we think there is a typo in the subnet mask of Fa0/0. It should not be ‘/26’ but longer one, ‘/28’, for example. So you should still choose answer C in this question.

Question 7


From the output we see the Serial0/0 of RouterA is in “status up/protocol down” state which indicates a Layer 2 problem so the problem can be:

+ Keepalives mismatch
+ Encapsulation mismatch
+ Clocking problem

Question 8


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.

+ 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

Comments (3) Comments
  1. Amy
    August 17th, 2017

    Is question 3 right??

  2. Mayya Gerrard
    August 20th, 2017

    hich interface counter can you use to diagnose a duplex mismatch problem?
    A. runts
    B. CRC errors
    C. no carrier
    D. late collisions
    E. deferred
    F. giants

    As i found on cisco and some other webpages, not CRC errors, but late collisions show us that there is a duplex missmatch issues. What is corect?

  3. ATL
    August 31st, 2017

    commonly cause LAN traffic congestion:

    CRC errors with absence of colliosons and late collisions when there excessive noise and or

    Cable damage on the link.
    1. Too many hosts in a collision or broadcast domain
    2. Broadcast storms – host experiences intermittent issues that relate to congestion
    Broadcast Storm: ignored and no buffer number increase
    3. Too much multicast traffic
    4. Low bandwidth
    5. Adding hubs for connectivity to the network
    6. A bunch of ARP broadcasts
    Duplex issuees
    – Collisions are a normal occurrence in half-duplex operation.
    Change the link to full-duplex to eliminate collisions.
    – Late Collisions occur when there are problems in a switched network, duplex mismatch
    – Typical duplex mismatch problems – full duplex side of link – high FCS errors
    half duplex side high late collisons
    verify the local IP stack you would ping the loopback
    Excessive noise and
    CRC accumulation