CCNA 200-125 Exam: EtherChannel Questions With Answers

  1. Refer to the exhibit. While troubleshooting a switch, you executed the “show interface port-channel 1 etherchannel” command and it returned this output. Which information is provided by the Load value?
    • A. the percentage of use of the link
    • B. the preference of the link
    • C. the session count of the link
    • D. the number source-destination pairs on the link*

    Show (Hide) Explanation/Reference
    The way EtherChannel load balancing works is that the switch assigns a hash result from 0-7 based on the configured hash method ( load balancing algorithm ) for the type of traffic. This hash result is commonly called as Result Bundle Hash (RBH).

    Now we need to convert Load value from Hexadecimal to Binary numbers. Therefore:
    + Gi1/1: 36 (Hex) = ‭00110110‬ (Bin) -> Bits 3, 4, 6, 7 are chosen
    + Gi1/2: 84 (Hex) = ‭10000100‬ (Bin) -> Bits 1, 6 are chosen
    + Gi1/3: 16 (Hex) = ‭00010110‬ (Bin) -> Bits 4, 6, 7 are chosen

    Therefore if the RBH is 3, it will choose Gi1/1. If RBH is 4, it will choose Gi1/1 and Gi1/3 interfaces. If RBH is 6 it will choose all three above interfaces. And the bit sharing ratio is 3:3:2 (from “No of bits” column) hence two links has higher probability of getting utilized as compared to the third link.

  2. What is the status of port-channel if LACP is misconfigured?
    • A. Forwarding
    • B. Enabled
    • C. Disabled*
    • D. Errdisabled

    Show (Hide) Explanation/Reference
    EtherChannel misconfiguration occurs when the channel parameters do not match on both sides of the EtherChannel, resulting in the following message:

    %PM-SP-4-ERR_DISABLE: channel-misconfig error detected on Po3, putting E1/3 in err-disable state

    Therefore from the output above we can see that when miconfigured, the physical (member) interface is put into err-disable state.

    But this question asks above “the status of port-channel” (not the physical member interface) so answer “Disabled” is a better choice.

  3. What parameter can be different on ports within an EtherChannel?
    • A. speed
    • B. DTP negotiation settings*
    • C. trunk encapsulation
    • D. duplex

    Show (Hide) Explanation/Reference
    All interfaces in an EtherChannel must be configured identically to form an EtherChannel. Specific settings that must be identical include:

    Speed settings
    Duplex settings
    + STP settings
    + VLAN membership (for access ports)
    + Native VLAN (for trunk ports)
    + Allowed VLANs (for trunk ports)
    Trunking Encapsulation (ISL or 802.1Q, for trunk ports)

  4. Which option is the industry-standard protocol for EtherChannel?
    • A. LACP*
    • B. PAGP
    • C. Cisco Discovery Protocol
    • D. DTP

    Show (Hide) Explanation/Reference
    LACP is the IEEE Standard (IEEE 802.3ad) and is the most common dynamic Etherchannel protocol, whereas PAgP is a Cisco proprietary protocol and works only between supported vendors and Cisco devices.
  5. Which mode are in PAgP? (Choose two)
    • A. Auto*
    • B. Desirable*
    • C. Active
    • D. Passive
    • E. On

    Show (Hide) Explanation/Reference
    There are two PAgP modes:

    Auto Responds to PAgP messages but does not aggressively negotiate a PAgP EtherChannel. A channel is formed only if the port on the other end is set to Desirable. This is the default mode.
    Desirable Port actively negotiates channeling status with the interface on the other end of the link. A channel is formed if the other side is Auto or Desirable.

    The table below lists if an EtherChannel will be formed or not for PAgP:

    PAgP Desirable Auto
    Desirable Yes Yes
    Auto Yes No

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