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EtherChannel Questions

April 13th, 2017 in SWITCH 300-115 Go to comments

Notes:

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:

+ on: the link aggregation is forced to be formed without any LACP negotiation. A port-channel is formed only if the peer port is also in “on” mode.
+ off: disable LACP and prevent ports to form a port-channel
+ 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:

+ on: The link aggregation is forced to be formed without any PAgP negotiation. A port-channel is formed only if the peer port is also in “on” mode.
+ off: disable PAgP and prevent ports to form a port-channel
+ 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.

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

Question 1

Explanation

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

LACP Active Passive
Active Yes Yes
Passive Yes No

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

PAgP Desirable Auto
Desirable Yes Yes
Auto Yes No

To form an Etherchannel both sides must use the same Etherchannel protocol (LACP or PAgP). According the two tables above we can see only “desirable” and “auto” (of PAgP) can form an Etherchannel bundle.

Note: If we want to use “on” mode, both ends must be configured in this “on” mode to create an Etherchannel bundle.

Question 2

Explanation

To form an Etherchannel both sides must use the same Etherchannel protocol (LACP or PAgP).

Question 3

Explanation

In this case the EtherChannel bundle was configured to load-balance based on the destination IP address but there is only one web server (means one destination IP address). Therefore only one of the EtherChannel links is being utilized to reach the web server. To solve this problem we should configure load-balancing based on source IP address so that traffic to the web server would be shared among the links in the EtherChannel bundle with different hosts.

Question 4

Question 5

Explanation

If one end is passive and another end is active then the EtherChannel will be formed regardless the two interfaces in the same switch use different modes and different load-balancing method. Switch 1 will load-balance based on destination IP while Switch2 will load-balance based on source MAC address.

Question 6

Explanation

When storm control is configured on an EtherChannel, the storm control settings propagate to the EtherChannel physical interfaces. In the “show etherchannel” command output, The storm control settings appear on the EtherChannel but not on the physical port of the channel.

Note: You cannot configure storm control on the individual ports of that EtherChannel.

Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2950/software/release/12-1_22ea/SCG/scg/swtrafc.html

Question 7

Explanation

Issue the port-channel load-balance {src-mac | dst-mac | src-dst-mac | src-ip | dst-ip | src-dst-ip | src-port | dst-port | src-dst-port | mpls} global configuration command in order to configure the load balancing.

Question 8

Explanation

A LACP port priority is configured on each port using LACP. The port priority can be configured automatically or through the CLI. LACP uses the port priority with the port number to form the port identifier. The port priority determines which ports should be put in standby mode when there is a hardware limitation that prevents all compatible ports from aggregating.

The syntax of LACP port priority is (configured under interface mode):

lacp port-priority priority-value

The lower the range, the more likely that the interface will be used for LACP transmission.

Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_2sb/feature/guide/gigeth.html

Question 9

Explanation

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

PAgP Desirable Auto
Desirable Yes Yes
Auto Yes No

For “on” mode, the link aggregation is forced to be formed without any PAgP negotiation. A port-channel is formed only if the peer port is also in “on” mode.

Question 10

Explanation

Interfaces Fa0/13 to Fa0/15 are bundled into Port-channel 12 and it is running with “desirable” mode -> it is using PAgP.

Comments
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  1. Speedy 6 Nipples
    March 20th, 2016

    Q10isWrong is correct, Q 10 is Wrong.
    The etherchannel is using the protocol-less configuration “On”
    If PAgP or LACP were in use, you would see those listed under the “Protocol” in the printout of “show etherchannel summary”

  2. Papan Jaka
    March 22nd, 2016

    Q3

    I think the answer is B (destination base)
    because there is only one source is there and that is the server
    So go to several destinations it should be destination base

    Can anybody tell me this ???

  3. FustratedCCNPLoser
    March 26th, 2016

    My exam was taken on 3/25/2016 as I ended up with a humiliating 643/1000. All my study material was from the CiscoPress eBook (300-115), CBT Nuggets, VCE dumps (191q) and Certprep. I put in 6-7 study hours a day for nearly a month to pass 300-115 with extreme confidence, but I was shot down when I was roasted by the exam. The latest dumps from this site only covered about 25% of the questions given, but all the Lab Sim simulation were correct as I had LACP with STP / HRSP / AAA. I was easily able to finish the lab sims on the exam with success but fell way short when it came the questions with educated guesses. I would like to know if anyone can help me out to receive the latest dumps soon. Thanks. c_brotha @ yahoo.com

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    April 1st, 2016

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  6. Milton
    May 13th, 2016

    2/16 dump (pass4sure) is almost spot on with the exam

    passed with a 979/1000

    aaa/VACL, LACP+STP sims + cdp / lldp drag & drop

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    if you go over the dumps once before the exam youre clear

  7. goforccna
    May 14th, 2016

    @Milton
    How about HSRP? Can you drop the detail configs you did on the exam – AAA and LACP + STP ?

  8. zhang
    May 15th, 2016

    Q4:

    the etherchannel is between the access switch and the manage server, it should clear the confusion, just check the Q1 of etherchannel questions 2 in the next page.

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    June 11th, 2016

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  10. Nosfera
    June 29th, 2016

    Sorry guys but i only see the explanations where is the questions ?

  11. blowout
    July 8th, 2016

    Speedy 6 Nipples is correct about Q10. The ‘desirable’ output in the show interface trunk command refers to the trunking protocol in use, not the port channel config. There is no correct answer listed for this question as the etherchannel mode is ‘on’.

  12. Anonymous
    July 17th, 2016

    Speedy 6 Nipples is right. Q10 is incorrect. all etherchannels are in mode on. “show interface trunk” shows that etherchannels are working as trunks with ISL encapsulation, and trunking mode is desirable. trunking mode is not related to etherchannel protocol.

  13. Anyone
    August 7th, 2016

    Question 10 is definitely wrong and the answer is very misleading. In the answer, the “Desirable” is referring to the Dynamic Trunking Protocol mode of “Dynamic Desirable” not the EtherChannel mode.

    I like this question because it’s thought provoking but there should be a fifth option…E. None of the above

    The EtherChannel “on” mode makes the interface into an EtherChannel without the assistance of a negotiation protocols like Port Aggregation Protocol (PAgP) or Link Aggregation Control Protocol (LACP).

    This is why you can not define the EtherChannel protocol (LACP nor PAgP) in your config and use “On”:

    interface range f0/11 – 12
    switchport trunk encapsulation isl
    switchport mode dynamic desirable
    channel-protocol PAgP
    channel-group 1 mode on

    Command rejected (Channel protocol mismatch for interface Fa0/11 in group 1): the interface can not be added to the channel group

    I bet most people believed this should work.

  14. eddy
    August 18th, 2016

    Wow. This is why this site is the best :)

    I’ve already studied for the exam and currently practising via dumps and lab sims from here..
    I came across Q10 and also answered B without much hesitation.. until I saw your comments.. “Speedy 6” and “Anyone” are right.. it is mode ON with “switchport mode dynamic desirable” configured on the Po12.

    If this question appears to me in the exam what should I answer if they are all wrong?
    I usually leave a comment in the exam when I think there’s no valid answer but I doubt if anyone is going to read it..

  15. moto
    August 20th, 2016

    where are the questions, they don’t show up on the above site

  16. Hank
    September 5th, 2016

    Question 10 is correct. PAgP has two modes: Desirable and Auto.

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    September 28th, 2016

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  18. Anonymous
    October 12th, 2016

    Q3
    EtherChannel load balancing can use MAC addresses, IP addresses, or Layer 4 port numbers with a Policy Feature Card 2 (PFC2) and either source mode, destination mode, or both. The mode you select applies to all EtherChannels that you configure on the switch. Use the option that provides the greatest variety in your configuration. For example, if the traffic on a channel only goes to a single MAC address, use of the destination MAC address results in the choice of the same link in the channel each time. Use of source addresses or IP addresses can result in a better load balance

  19. SSR
    October 30th, 2016

    Q10
    The reasoning provided is wrong but the answer is B. The trunk encapsulation protocol listed in the exhibit is ISL which is cisco proprietary which implies that both switches have to be of CISCO. On the other hand, PAgP is another proprietary protocol and can’t work with other vendors. That’s why the correct answer is PAgP not “on”.

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    Ebay is legit. Passed the exam today. Good thing I came across this yesterday, was struggling with the LACP STP simulation but their instructions cleared up my confusion. You need to do trunk configs on the physical ports first, then add them into the port-channel.

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  39. Anonymous
    April 25th, 2017

    can anyone help whats is the answer for this question
    1.An engineer is configuring EtherChannel between two switches and notices the console message on switch 2. Based on the output, which option describes the
    reason for this error?

    A. Switch 1 does not have enough member ports configured.
    B. Switch 2 has too many member ports configured.
    C. The port channel interface numbers do not match.
    D. The EtherChannel protocols do not match.

    and why?

  40. Anonymous
    April 25th, 2017

    Which two statements about SPAN source and destination ports during an active session are true? (Choose two.)
    A. The source port can be only an Ethernet physical port.
    B. The source port can be monitored in multiple SPAN sessions.
    C. The destination port can be destination in multiple SPAN sessions.
    D. The destination port does not participate in STP.
    E. You can mix individual source ports and source VLANs within a single session.

  41. Rialunzu
    April 29th, 2017

    Which two statements about SPAN source and destination ports during an active session are true? (Choose two.)
    A. The source port can be only an Ethernet physical port.
    B. The source port can be monitored in multiple SPAN sessions.
    C. The destination port can be destination in multiple SPAN sessions.
    D. The destination port does not participate in STP.
    E. You can mix individual source ports and source VLANs within a single session.

    Answer: B, D

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