Home > EtherChannel Questions 2

EtherChannel Questions 2

May 6th, 2015 in SWITCH 300-115 Go to comments

Question 1

Explanation

From the output we see currently the Server_Switch is load balancing via source MAC address. By changing load-balance to another method the problem can be solved. In this case C is the best choice because other answers are surely incorrect.

Question 2

Explanation

Configuration changes applied to the port-channel interface apply to all the physical ports assigned to the port-channel interface. Configuration changes applied to the physical port affect only the port where you apply the configuration. To change the parameters of all ports in an EtherChannel, apply configuration commands to the port-channel interface, for example, spanning-tree commands or commands to configure a Layer 2 EtherChannel as a trunk.

Note: If we only change the parameters on a physical port of the port-channel, the port-channel may go down because of parameter mismatch. For example, if you only configure “switchport trunk allowed vlan …” on a physical port, the port-channel will go down.

Question 3

Explanation

The EtherChannel provides full-duplex bandwidth up to 800 Mbps (Fast EtherChannel) or 8 Gbps (Gigabit EtherChannel) between your switch and another switch or host.

Each EtherChannel can consist of up to eight compatibly configured Ethernet interfaces. All interfaces in each EtherChannel must be the same speed, and all must be configured as either Layer 2 or Layer 3 interfaces.

Note: 800 Mbps full-duplex means data can be transmitted at 800 Mbps and received at 800 Mbps (1600 Mbps in total).

Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3550/software/release/12-1_13_ea1/configuration/guide/3550scg/swethchl.html

Question 4

Explanation

From the last line of the output, we learn physical ports Fa0/13, Fa0/14, and Fa0/15 are bundled into Port-channel 1 and use LACP which is an open standard protocol.

Question 5

Explanation

The EtherChannel provides full-duplex bandwidth up to 800 Mbps (Fast EtherChannel) or 8 Gbps (Gigabit EtherChannel) between your switch and another switch or host. Therefore if we have 10 Gigabit Ethernet connections, only 8 links will be used.

Question 6

Explanation

Multichassis LACP (mLACP) is also supported on 7600 and ASR9000 series -> A is not correct.

mLACP supports both FastEthernet & GigabitEthernet -> B is not correct.

VSS mode does not support the mLACP for server access feature only. But mLACP is available in Virtual Switching Systems (VSS). An example of combination of VSS and mLACP is shown below:

mLACP_VSS.jpg

In the topology above, the mLACP is a port channel that spans the two chassis of a VSS. Notice that the two chassis of this VSS is connected via a Virtual Switch Link (VSL). VSL is a special link that carries control and data traffic between the two chassis of a VSS. In this case the VSL is implemented as an EtherChannel with two links.

Some of the restrictions for mLACP are mentioned at http://www.cisco.com/c/en/us/td/docs/routers/asr920/configuration/guide/lanswitch/lanswitch-ethernet-channel-xe-3s-asr920-book/lsw_mlacp.html

+ mLACP does not support Fast Ethernet.
+ mLACP does not support half-duplex links.
+ mLACP does not support multiple neighbors.
+ Converting a port channel to mLACP can cause a service disruption (in a short time) -> D is not correct.

Question 7

Explanation

When enabled, LACP tries to configure the maximum number of LACP-compatible ports in a channel, up to a maximum of 16 ports. Only eight LACP links can be active at one time. The software places any additional links in a hot-standby mode. If one of the active links becomes inactive, a link that is in the hot-standby mode becomes active in its place.
If you configure more than eight links for an EtherChannel group, the software automatically decides which of the hot-standby ports to make active based on the LACP priority. The software assigns to every link between systems that operate LACP a unique priority made up of these elements (in priority order):
+ LACP system priority
+ System ID (a combination of the LACP system priority and the switch MAC address)
+ LACP port priority
+ Port number
In priority comparisons, numerically lower values have higher priority. The priority decides which ports should be put in standby mode when there is a hardware limitation that prevents all compatible ports from aggregating.
Ports are considered for active use in aggregation in link-priority order starting with the port attached to the highest priority link. Each port is selected for active use if the preceding higher priority selections can also be maintained. Otherwise, the port is selected for standby mode.

(Reference: http://www.cisco.com/c/en/us/td/docs/switches/metro/me3600x_3800x/software/release/12-2_52_ey/configuration/guide/3800x3600xscg/swethchl.html#wp1144010)

Question 8

Explanation

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

LACP Active Passive
Active Yes Yes
Passive Yes No

Therefore if switch 1 is configured LACP in active mode, the other end must be configured as Active or Passive mode.

Note: If the other end is configure with “On” mode, the EtherChannel will not be formed because in “On” mode, no negotiation is sent so the neighbor cannot receive any EtherChannel information.

Question 9

Explanation

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 the way you want. For example, assign access/trunk mode on switches or assign IP address for the logical interface on routers/Layer 3 switches… An example of a Layer 3 Etherchannel port is shown below:

interface PortChannel12
description Link to R2
ip address 10.2.4.13 255.255.255.252

Question 10

Explanation

To configure EtherChannel load balancing, “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”. Therefore only the “source MAC address and destination MAC address” answer is correct.

Reference this link: http://www.cisco.com/c/en/us/support/docs/lan-switching/etherchannel/12023-4.html

Question 11

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.

Comments
  1. steve
    April 24th, 2015

    Answer in Q1 I think is wrong because if you load balance based on dst-mac, all traffic will pass in one link only.

  2. Liam
    April 24th, 2015

    Can someone confirm the Answer to Question 3?

    Page 245 of the SWITCH 300-115 Offical Cert Guide clearly states ‘This bundle provides a Full-duplex bandwidth of up to 1600 Mbps (FastEthernet) 16Gbps (eight links of GE)’, meaning the answer to Question 3 is not actually listed?

    Answer A has 800Mbps and 8Gbps which is half of a full-duplex 8 Port bundle and Answer C although says 16Gbps, has 800Mbps for Fast Ethernet. I may be interpreting it wrong but something clearly doesn’t match up here

  3. Need Helping
    May 1st, 2015

    @ Liam, yes i do agree with you as we have alway been referred with 1600Mbps cos is full duplex, and 16Gbps for gig port. If you look at the book at page 241, first question it ask how much will be the bandwith of an etrhechannel. The answer on the book is letteg e. and the value in there is 16Gbps. So now is down to the examiner to confirm is it is a marketing value or a technical value. Is all in their hands on how do they want to advertise the product.

  4. hadi
    May 3rd, 2015

    anwser for q5 is incorrect?

    http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/31sg/configuration/guide/conf/channel.html

    summery:
    therChannel bundles individual Ethernet links into a single logical link that provides bandwidth up to 1600 Mbps (Fast EtherChannel full duplex),16 Gbps (Gigabit EtherChannel), or 40 Gbps (10 Gigabit Etherchannel) between a Catalyst 4500 series switch and another switch or host.

    i am confused

  5. ECM
    May 4th, 2015

    @hadi Q5 Is correct!

    Cisco EtherChannel connections can consist of one to eight industry-standard Fast Ethernet links to load share traffic with up to 80 Gbps of usable bandwidth. EtherChannel connections can interconnect LAN switches, routers, servers, and clients. Because load balancing is integrated with Cisco Catalyst® LAN switch architectures, there is no performance degradation for adding links to a channel—high throughput and low latencies can be maintained while gaining more available bandwidth.

    http://www.cisco.com/en/US/tech/tk389/tk213/technologies_white_paper09186a0080092944.shtml

  6. UNiX
    May 26th, 2015
  7. Adriana
    June 8th, 2015

    Quetion 1 is correct, because the server has 2 NICs which means it has 2 MAC addresses, one connected to each switch port!

  8. Pratik D
    July 18th, 2015

    Q3 wrong.

    correct answer

    A switch can support up to eight compatibly configured Ethernet interfaces in an EtherChannel. The EtherChannel provides full-duplex bandwidth up to 1600 Mbps only for Fast EtherChannel or 16 Gbps only for Gigabit EtherChannel.
    for Fast ethernet :- 100×2 = 200 /Interface
    =200×8=1600/interface Mbps

    for gigabit ethernet :- 1000×2= 2000/Interface
    2000×8=16000/interface i.e 16Gbps

  9. The Watcher
    August 29th, 2015

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  10. Anonymous
    October 13th, 2015

    Explanation to Q1 is a weak and untenable argument. I’m not saying that answer is wrong but it’s a clear guess and logically, load balancing based on dst-mac will send traffic over only one link – as someone pointed out. Can anyone think of a better explanation?

  11. CCNPtaker
    November 3rd, 2015

    LOL at explanation at Q1. doesnt justify anything, what a shame

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    November 5th, 2015

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    November 19th, 2015

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  14. Luis
    December 3rd, 2015

    I think that the answer for Q1 is correct, here is the explanation from the official cert guide: “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.”

  15. Jen
    December 4th, 2015

    Hi All,
    I only see answers. Where are the questions? Thanks!

  16. CCNPtaker
    December 13th, 2015

    i found out now the explanation for Q1. Because the server has 2 nics.

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    December 22nd, 2015

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    January 6th, 2016

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  22. Anonymous
    January 13th, 2016

    hy for Q6, mLACP support or doesn’t support FastEthernet ?

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    March 26th, 2016

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  28. ccnplearner
    September 15th, 2016

    change option in q6, the answer is correct but mlacp doesn’t support fast ethernet but it does support gigabitethernet hereby the 1gbs

  29. cg
    October 21st, 2016

    Etherchannel2 Q6
    so does mLACP Support FE in Etherchannel or not?
    For ASR 920 it’s clear, they don’t. What about other platforms (c6k, c4k) ?!

  30. cg
    October 23rd, 2016

    etherchannel 2 Q1
    answer C looks right because the others lead to nothing, but it wouldn’t help in real life:
    the server may have a problem with performance or the server should load-balance better over the two ports. I do not think the requests are coming slow to the server (their balancing is now leading to use one port in direction towards the server). It might turn out to be useful as possible channels from server switch to the network could be tuned.

  31. cg
    October 23rd, 2016

    Q3 opens again the question how to rate bandwidth at full duplex

    This is a good example for a non concise manner

  32. rava
    October 25th, 2016

    @cg

    mLACP doesnt support FE
    google this ” Restrictions for mLACP ”

    so c) is correct

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    October 28th, 2016

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  34. SSR
    October 30th, 2016

    Q3, correct answer is A.
    Bandwidth of 1 Gig link is 1000 MBps where its throughput is 2000 Mbps full duplex.
    so for that reason BW=8*1000 or throughput = 8*2000 will give you the right answer.

  35. Paul
    November 6th, 2016

    In question #6.

    mLACP supports both FastEthernet & GigabitEthernet

    + mLACP does not support Fast Ethernet.

    Which is the correct ?????

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  45. Anonymous
    February 9th, 2017

    Today I pass switch exam with 912. This site was enought to pass the switch exam. But you need new 14 + 201 question. And then Itt found I new question about Etherchannel. The question is asking about what value must match between two switch when deploy etherchannel. answer are

    (A) Spanning tree port priority
    (B) Spanning Tree cost
    (C) interface Description
    (D) Trunk port mode
    (E) Trunk port allow vlan

    I select D,E. Because spanning tree wasn’t need to think during etherchannel. Interface Descripition is also need. So answer is D and E.

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