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EtherChannel Questions 3

November 22nd, 2018 in SWITCH 300-115 Go to comments

Question 1

Explanation

From the outputs of the “show etherchannel summary” commands we learn that Switch1 is configuring EtherChannel with LACP while Switch2 is configuring with EtherChannel “on” mode -> the EtherChannel bundle does not go up.

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Explanation

You can determine if your port has been error disabled if you issue the “show interfaces” command.

cat6knative#show interfaces gigabitethernet 4/1 status
Port Name   Status       Vlan Duplex Speed Type
Gi4/1       err-disabled 100  full   1000  1000BaseSX

Reference: https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/69980-errdisable-recovery.html

Therefore we can check these attributes: VLAN, Duplex and Status. “Status” here can be considered the “port mode” (errdisabled mode) so in fact there are three correct answers in this case. But we should choose “VLAN” and “Duplex” which are obviously correct.

Question 8

Question 9

Explanation

By default, when an LACP channel is configured, the LACP channel mode is passive.

Reference: http://www.cisco.com/c/en/us/support/docs/lan-switching/etherchannel/19642-126.html

Question 10

Explanation

From the output above, we see the “Protocol” field is empty (with a “-” sign). Therefore we can conclude it does not run any EtherChannel protocol (mode “on”). This EtherChannel is up with “(SU)” keywords (“S” means “Layer 2” and “U” means “up”) -> This is an Layer 2 EtherChannel mode “on”.

Comments
  1. mikeSWE
    July 19th, 2017

    q6. other dumps are giving different answers please confirm @Certprepare

  2. Ovione
    August 22nd, 2017

    Hello q6 which is it? C or D? Thanks

  3. Anonymous
    August 23rd, 2017

    Q6 : D. Destination MAC

  4. noob
    August 23rd, 2017

    On Q6 the answer is D. Destination MAC. You have only one bradcast domain.

  5. Anonymous
    September 10th, 2017

    Question 2
    There was an EtherChannel configured and one of the port was used as SPAN destination. What will be the result?
    A. the EtherChannel will not be operational because the port cannot be used as SPAN destination B. EtherChannel will discard the port used C. the EtherChannel will shutdown

    Answer A

    as oer https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/10570-41.html#anc63

    Can You Configure SPAN on an EtherChannel Port?

    An EtherChannel does not form if one of the ports in the bundle is a SPAN destination port. If you try to configure SPAN in this situation, the switch tells you:
    Channel port cannot be a Monitor Destination Port
    Failed to configure span feature
    You can use a port in an EtherChannel bundle as a SPAN source port.

  6. NJ
    October 15th, 2017

    Question 2
    I am confused with this.

    https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/10570-41.html

    Characteristics of Destination Port:
    A destination port can be a physical port that is assigned to an EtherChannel group, even if the EtherChannel group has been specified as a SPAN source. The port is removed from the group while it is configured as a SPAN destination port.

    So the answer is B?

  7. Al
    October 23rd, 2017

    Q 2
    The answer is B.
    Suppose that 5 ports from switch A (13-17) and 5 ports from switch B (13-17) are taking part in creating Po1. If I use port 14 on the switch 2 as the destination of Monitor session 5, then the outcome is as follows:
    Show ip int brief shows port 14 on the both switches as up down.
    Sh ether sum will show the port 14 on the switch B (the switch with SPAN set up) as (D) down, however, the other switch will show its own 14’s port as suspended.
    So I gather that the switch B will cast out its port 14, because it does not conform with the rules of Etherchannel. And as a result, port 14 on the other switch goes down. However, the rest of the Etherchannel (13,15,16,17) from both switches will continue setting up a healthy port-channel.

    Thanks

  8. Al
    October 23rd, 2017

    Apologies, switch B instead of switch 2 in the line 4.

  9. YMD
    November 7th, 2017

    Q6: This question misses information: which interface are you configuring, and/or what are the switch types. Destination mac/ip only works upsteam. Downstream you’d want source. Ideally, you’d just do source-dest on both…

  10. oval
    November 7th, 2017

    Q6 – I’m having trouble in identifying which side should I consider as source or destination. If we consider to be on the servers side, shouldn’t it be answer A. Source MAC?

  11. Hank
    November 15th, 2017

    Q6:
    The correct answer is B: src and dest MAC address. It needs to be both in order to handle traffic for both directions. If you choose only MAC or IP, it only works for 1 direction.

    *The SRC address is the bottom switch, and the Dest address is the upper switch going from the PC. Then, they are reversed when coming from the servers. The question is only concerned with the Etherchannel link. Not the PC or the servers.

  12. Jack
    November 26th, 2017

    Question 9:
    After LACP is enabled, you configure each link or the entire channel as active or passive.
    When you run port channels with no associated protocol, the port-channel mode is always on.
    The default port-channel mode is on.

    hence the Answer is On.

  13. ciptech
    December 5th, 2017

    “passive – Enables LACP only when an LACP device is detected. This is the default state.”

    https://www.cisco.com/c/en/us/td/docs/optical/cpt/r9_3/command/reference/cpt93_cr/cpt93_cr_chapter_01000.html

    @bigM & @Jack that is for NX-OS which is used on equipment suitable for Data Center not enterprise network.

  14. Addie
    December 5th, 2017

    Still doubts on Q6

  15. RA
    December 7th, 2017

    Note: By default, when an LACP channel is configured, the LACP channel mode is passive.

  16. Lunchi
    January 14th, 2018

    Q7

    There are various reasons for the interface to go into errdisable. The reason can be:

    Duplex mismatch

    Port channel misconfiguration

    BPDU guard violation

    UniDirectional Link Detection (UDLD) condition

    Late-collision detection

    Link-flap detection

    Security violation

    Port Aggregation Protocol (PAgP) flap

    Layer 2 Tunneling Protocol (L2TP) guard

    DHCP snooping rate-limit

    Incorrect GBIC / Small Form-Factor Pluggable (SFP) module or cable

    Address Resolution Protocol (ARP) inspection

    Inline powe

  17. Student
    January 16th, 2018

    Queation 7 it’s can be answer a,c,e
    Help pls

  18. Doc
    January 29th, 2018

    Hi,

    Q6. It msut be Destination MAC, because source is only one and there is no L3 Device. So We working with MAC only. So destination MAC is correct.

  19. Anonymous
    February 6th, 2018

    Q7 A,C,E seems to me correct please help !!!

  20. Tinman
    March 17th, 2018

    Question 4
    If the switch detects a misconfiguration on the other device, EtherChannel guard places the switch interfaces in the error-disabled state, and displays an error message.
    You can enable this feature by using the spanning-tree etherchannel guard misconfigglobal configuration command.

    https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750x_3560x/software/release/12-2_55_se/configuration/guide/3750xscg/swstpopt.html#52777

  21. Anthony
    April 14th, 2018

    Question 8 seems to be odd.

    ‘A’ is also correct as LACP priority is used to both determine which ports will form Etherchannel and which ports remain in standby mode

  22. lalaversa
    May 4th, 2018

    Q6.
    The flow of traffic from/to is not explained and the question asks how to optimize etherchannel between switches. If the single PC contacts the two servers at the top maybe it is more correct that the answer D (Destination MAC) is the most correct one.
    In the opposite case, however, for the two desktops that contact the PC the answer A (Source MAC) would be more suitable.
    Usual question made to do just so much confusion …

  23. lalaversa
    May 4th, 2018

    Q7.
    Port mode indicate if it’s an access or a trunk port and it’s not a correct answer because for the connection is importante the same VLAN are on both sides of the etherchannel.
    B & D answers are fake. Correct answers are C (Duplex) and E (VLAN).

  24. kingkong21312
    May 30th, 2018

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  25. Enhinyerong Pinoy
    July 25th, 2018

    Try Simulating it or run on actual device to further verify your concern. thanks!

  26. Anonymous
    October 12th, 2018

    @lalaversa
    Definitelly not C, how can you check the duplex if port is down?

  27. sky
    December 17th, 2018

    So, default mode for LACP is passive:
    passive (Default for LACP) LACP mode that places a port into a passive negotiating state, in which
    the port responds to LACP packets it receives but does not initiate LACP negotiation.
    active LACP mode that places a port into an active negotiating state, in which the port initiates
    negotiations with other ports by sending LACP packets.
    https://www.cisco.com/c/en/us/td/docs/routers/7600/ios/15S/configuration/guide/7600_15_0s_book/channel.pdf

  28. land
    February 23rd, 2019

    Can anyone help explain Q1? How can you know Switch2 is in on mode? Also, why does Switch1 have only port Fa1/0/23 (NOT Fa1/0/23 and Fa1/0/24) in the output of show etherchannel summary command?

    Thank you.

  29. yavor
    April 10th, 2019

    For Q6. The most appropriate answer should be D. It asks in the question as well.
    As the IP of the servers and the PC is always a constant value. And usually PC/servers communicate based on IP addresses.
    The load balancing method uses XOR operations to determine on which link it should forward the frame.
    If we assume that Server 1 has IP 172.31.67.46 and Server 2 172.31.67.47 while the PC is with 192.168.1.1 the calculations are following.
    3 right most bits are taken from the IP for an 8 ethch. link. As 2x2x2 gives 8.

    So the last 3 right most bits from the last octet are:
    S1 s2 PC
    110 111 001
    This is a 2 link ether channel so important is the last bit.
    The last bits are 0 – 1 – 1. So 0 XOR 1 or 1XOR 1 away gives 1 and most of the times only link 1 will be utilized which leads to unefficient load balancing using the dest IP.The question asks to optimize the link.

    Also in the official guide for the CCNP switch it is written:

    “For example, if a single server is receiving most of the traffic on an
    EtherChannel, the server’s address (the destination IP address) always will remain constant in the many conversations.
    This can cause one link to be overused if the destination
    IP address is used as a component of a load-balancing method.
    Configuring the use of MAC addresses, or only the source IP addresses, might cause the distribution to be more balanced across all the bundled links.”

  30. QA
    July 10th, 2019

    Q6: From the switch foundation guide:

    If most of the traffic is IP, it makes sense to load balance according to IP addresses or port numbers. For non-IP traffic, the hash uses MAC addresses to calculate the path.

    So probably C is the ‘best’ answer as client/servers are involved e.g. for web, file, email based services and all IP based

    http://www.ciscopress.com/articles/article.asp?p=2348266&seqNum=3

  31. xor gates…
    September 15th, 2019

    XOR, or exclusive or, means 1XOR1 is not 1, it’s 0. hence the “exclusive” designation.

    just wanted to clear that up…

    the real answer should be src-dst mac, in my opinion (B) as it would increase the likelihood that flows from PC to SV1 would ride a different link than PC to SV2.

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