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Etherchannel Questions

February 7th, 2021 Go to comments

Quick overview of EtherChannel:

EtherChannel bundles the physical links into one logical link with the combined bandwidth and it is awesome! STP sees this link as a single link so STP will not block any links! EtherChannel also does load balancing among the links in the channel automatically. If a link within the EtherChannel bundle fails, traffic previously carried over the failed link is carried over the remaining links within the EtherChannel. If one of the links in the channel fails but at least one of the links is up, the logical link (EtherChannel link) remains up. EtherChannel also works well for router connections: EtherChannel_router.jpg When an EtherChannel is created, a logical interface will be created on the switches or routers representing for that EtherChannel. You can configure this logical interface in the way you want. For example, assign access/trunk mode on switches or assign IP address for the logical interface on routers…

Note: A maximum of 8 Fast Ethernet or 8 Gigabit Ethernet ports can be grouped together when forming an EtherChannel. There are three mechanisms you can choose to configure EtherChannel:
+ Link Aggregation Control Protocol (LACP)
+ Port Aggregation Protocol (PAgP)
+ Static (“On”)

The Port Aggregation Protocol (PAgP) and Link Aggregation Control Protocol (LACP) facilitate the automatic creation of EtherChannels by exchanging packets between Ethernet interfaces. The Port Aggregation Protocol (PAgP) is a Cisco-proprietary solution, and the Link Aggregation Control Protocol (LACP) is standards based.

LACP modes:

LACP dynamically negotiates the formation of a channel. There are two LACP modes:

+ passive: the switch does not initiate the channel, but does understand incoming LACP packets
+ active: send LACP packets and willing to form a port-channel

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

LACP Active Passive
Active Yes Yes
Passive Yes No

PAgP modes:

+ desirable: send PAgP packets and willing to form a port-channel
+ auto: does not start PAgP packet negotiation but responds to PAgP packets it receives

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

PAgP Desirable Auto
Desirable Yes Yes
Auto Yes No

An EtherChannel in Cisco can be defined as a Layer 2 EtherChannel or a Layer 3 EtherChannel.
+ For Layer 2 EtherChannel, physical ports are placed into an EtherChannel group. A logical port-channel interface will be created automatically. An example of configuring Layer 2 EtherChannel can be found in Question 1 in this article.

+ For Layer 3 EtherChannel, a Layer 3 Switch Virtual Interface (SVI) is created and then the physical ports are bound into this Layer 3 SVI.

Static (“On”)

In this mode, no negotiation is needed. The interfaces become members of the EtherChannel immediately. When using this mode make sure the other end must use this mode too because they will not check if port parameters match. Otherwise the EtherChannel would not come up and may cause some troubles (like loop…).

Note: 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)

Note: EtherChannels will not form if either dynamic VLANs or port security are enabled on the participating EtherChannel interfaces.

For more information about EtherChannel, please read our EtherChannel tutorial.

Question 1


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

Question 2


The Cisco switch was configured with PAgP, which is a Cisco proprietary protocol so non-Cisco switch could not communicate.

Question 3


In this case, we are using your EtherChannel without a negotiation protocol. As a result, if the opposite switch is not also configured for EtherChannel operation on the respective ports, there is a danger of a switching loop. The EtherChannel Misconfiguration Guard tries to prevent that loop from occuring by disabling all the ports bundled in the EtherChannel.

  1. Fahd
    March 18th, 2020

    Hi Guys,

    Any advice for me as a beginner for this tutorial?

  2. digitaltut
    March 19th, 2020

    @Fahd: You can find out more about Etherchannel at: https://www.9tut.com/etherchannel-tutorial

  3. Hussain
    March 27th, 2020

    Hi Brothers
    can any one tell where is LABs

  4. Anonymous
    March 27th, 2020

    this is any my topic for Python

  5. Anonymous
    April 2nd, 2020

    I understand there are no labs.

  6. Taurus
    April 18th, 2020

    where can i find questions ?

  7. Vizar
    May 4th, 2020

    Hi. has anyone taken the new Encore R&S exam? how much different is the new exam? what % of exam questions are found on the 9-tut website? can you share your experiences?

  8. Abdul
    May 26th, 2020

    I can not see the Qs just the explanations?

  9. El Boobie
    June 2nd, 2020

    You have to Pay for premium to see the full content guys :) Its not that expensive.

  10. Anonymous
    June 8th, 2020


  11. Anonymous
    June 15th, 2020

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  12. mirekivalla
    July 1st, 2020

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  13. Anonymous
    July 5th, 2020

    Can someone please share pdf containing questions along with answers…

  14. Vale
    July 31st, 2020

    I have the last exam of this week write me to valenciaeduardo453 at gmail dot com

  15. wadadli
    August 31st, 2020

    Hi guys I am not seeing the questions, and solution?

  16. Taygun88
    October 19th, 2020

    Hi guys, I see just 2 questions, is this correct?
    There are just 2 questions in ETHERCHANNEL part? am I correct?

  17. ClintEastwood
    October 19th, 2020

    By process of elimination the answer is definitely A. It cannot “native vlan” is not part of the configuration. There is no information what SW2 is set to, so it cannot be C. The thing applies to D so the nswer is A

  18. Anonymous
    November 16th, 2020

    @digitaltut why the flash links are gone?

  19. digitaltut
    November 16th, 2020

    @Anonymous: We removed them as Flash is going to be unsupported at the end of 2020. Some of the questions in them are not updated with correct answers too.

  20. ahmed
    December 23rd, 2020

    where the questions guys ?

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    March 2nd, 2021

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    March 3rd, 2021

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  23. olegius
    March 26th, 2021

    Q3 It is possible that the correct answer is C, not A.
    No ports are specified in the show etherchannel summary command output.

  24. olegius
    March 26th, 2021

    The protocol is optional.

  25. Anonymous
    March 27th, 2021


    I’m relatively certain is a native VLAN mismatch. We don’t see any configuration lines for the native VLAN, and only VLANS 10-100 are allowed over the link (not the default native VLAN: 1)

    Per https://www.cisco.com/c/en/us/support/docs/switches/catalyst-2950-series-switches/24042-158.html a native VLAN mismatch will cause negotiation to fail.

    We also see the encapsulation method is dot1q, which is short for 802.1q (an IEEE standard, not Cisco proprietary), which seems to rule out option A.

  26. olegius
    March 30th, 2021

    Q3 Created the lab and checked everything. Correct answer A. The error message appears only if there is no protocol on one side or protocol misconfig. The ports are sent to the error-disabled state by STP.
    02:01:19.229: %PM-4-ERR_DISABLE: channel-misconfig (STP) error detected on Fa1/0/1, putting Fa1/0/1 in err-disable state
    02:01:19.254: %PM-4-ERR_DISABLE: channel-misconfig (STP) error detected on Fa1/0/2, putting Fa1/0/2 in err-disable state
    If there are no ports in Port-channel, then the message is not generated. STP just blocks one of the ports.

  27. ENCOR
    June 16th, 2021

    Please send me a valid Dump to nadim-sharabaty at outlook dot com

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    June 18th, 2021

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    June 29th, 2021

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