EtherChannel Questions
If you are not sure about EtherChannel, please read our EtherChannel tutorial.
Question 1
Explanation
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.
Question 2
Explanation
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.
Question 3
Explanation
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)
Question 4
Explanation
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.
Question 5
Explanation
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 6
Explanation
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)
In the output of the “show interface fa0/1” commands we see the speed of interface Fa0/1 of SW1 is “100Mb/s” while that of SW2 is “10Mb/s” so the speed is mismatched here -> an Etherchannel will not be formed.
What is the status of port-channel if LACP is misconfigured?
A. Forwarding
B. Enabled
C. Disabled
D. Errdisabled
Hi can you please explain why C is the answer and not D
@Tomorrow Exam the answer is C which is Disabled
@9Tut what is the correct answer for 4th question is it Disabled state or Errordisabled state.
Torrow exams, the Errdisabled is a port-security violation state, which you will get when you configure port security with security violation on a switchport.. The etherchannel port will be disabled if the parameters of LACP configuration are not met at both ends.. Exam when bot end of the link are configure with passive, the LACP link is disabled.. so we have port status in LACP as diasbled, Passive, Active en on. where on-on will active the link, Active-passive will activate the link .
Can someone explain this
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?
Etherchannel_show_interface_port-channel.jpg
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
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New Ques. which command enable neighbor discovery in multi vendor environment?
A. lldp transmit
B. lldp receive
C. cdp run
D. lldp run
Ans. D
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this link suggests the answer is errdisable:
https://supportforums.cisco.com/t5/network-infrastructure-documents/port-status-is-errdisable-due-to-etherchannel-misconfiguration/ta-p/3131226
Q2:
What is the status of port-channel if LACP is misconfigured?
A. Forwarding
B. Enabled
C. Disabled
D. errdisabled
Chinese Dumps answer: D
9tut answer: C
what is correct ? There is no “disable” state for a LACP.
Regarding Q2:
There is actually an err-disable state for a lacp:
*Mar 1 05:43:12.698: %PM-4-ERR_DISABLE: channel-misconfig (STP) error detected on Po12, putting Po12 in err-disable state
Don’t have a chance to test it with PT or GNS3 right now, anyone who can help on this ?
MarcoC
Yeah, I think 9tut is overthinking this one based on the wording of the question. I believe the answer is Errdisable, and a few other places I’ve looked at agree. Actually, I think 9tut is the only place who says disabled. Everyone else says Errdisabled. I’m set to take the test next week, and if this question pops, I’m putting Errdisabled.
The answer is err-disable for any channel-misconfig (STP) error detected on P01 in er-disable state
Q2
The explanation is quite self explainatory.
“%PM-SP-4-ERR_DISABLE: channel-misconfig error detected on Po3, putting E1/3 in err-disable state”
“putting E1/3 in err-disable state” – putting interface in error disable state.
Therefore, the correct answer is D.
9tut, pl fix this.
@Sinix,
Physical interface goes to ERR-DISABLE state, but question is what is happening with port-channel. Port-channel, as a group of physical interfaces, goes to DISABLED state. C is correct.
9tut, where are the the questions for these answers? Please help us.
u can get question link from faq section
Created a lab for the question 2 about LACP:
What is the status of port-channel if LACP is misconfigured?
A. Forwarding
B. Enabled
C. Disabled <<<<<<<<< Correct Answer
D. errdisabled
##########################################################
++ SW-1 config ++
interface GigabitEthernet0/2
switchport trunk encapsulation dot1q
negotiation auto
channel-group 1 mode passive
!
interface GigabitEthernet0/3
switchport trunk encapsulation dot1q
negotiation auto
channel-group 1 mode passive
++ SW-2++
interface GigabitEthernet0/2
switchport trunk native vlan 2
switchport mode access
negotiation auto
channel-group 1 mode passive
!
interface GigabitEthernet0/3
switchport trunk native vlan 2
switchport mode access
negotiation auto
channel-group 1 mode passive
##########################################################
Port status after configuration applied.
SW-1(config-if-range)#
Oct 27 23:41:53.968: %EC-5-CANNOT_BUNDLE2: Gi0/2 is not compatible with Po1 and will be suspended (trunk mode of Gi0/2 is dynamic, Po1 is access)
Oct 27 23:41:54.113: %EC-5-CANNOT_BUNDLE2: Gi0/3 is not compatible with Po1 and will be suspended (trunk mode of Gi0/3 is dynamic, Po1 is access)
Oct 27 23:41:55.834: %LINK-3-UPDOWN: Interface GigabitEthernet0/2, changed state to up
Oct 27 23:41:55.981: %LINK-3-UPDOWN: Interface GigabitEthernet0/3, changed state to up
Oct 27 23:41:56.834: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthe rnet0/2, changed state to up
Oct 27 23:41:56.981: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthe rnet0/3, changed state to up
SW-1(config-if-range)#^Z
SW-1#
SW-1#
SW-1#
Oct 27 23:42:33.166: %SYS-5-CONFIG_I: Configured from console by consoleshow ip int bri
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 unassigned YES unset up up
GigabitEthernet0/1 unassigned YES unset up up
GigabitEthernet0/2 unassigned YES unset up up
GigabitEthernet0/3 unassigned YES unset up up
Port-channel1 unassigned YES unset down down <<<<<<<<<<<<<
Vlan1 10.1.1.10 YES manual up up
SW-1#s
SW-2(config-if-range)#
*Oct 27 22:58:25.247: %EC-5-CANNOT_BUNDLE2: Gi0/2 is not compatible with Po1 an will be suspended (dtp mode of Gi0/2 is off, Po1 is on)
*Oct 27 22:58:25.247: %EC-5-CANNOT_BUNDLE2: Gi0/3 is not compatible with Po1 an will be suspended (dtp mode of Gi0/3 is off, Po1 is on)
*Oct 27 22:58:26.978: %LINK-3-UPDOWN: Interface GigabitEthernet0/2, changed stae to up
*Oct 27 22:58:27.115: %LINK-3-UPDOWN: Interface GigabitEthernet0/3, changed stae to up
*Oct 27 22:58:27.978: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEternet0/2, changed state to up
*Oct 27 22:58:28.115: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEternet0/3, changed state to up
SW-2(config-if-range)#show ip int bri
^
% Invalid input detected at '^' marker.
SW-2(config-if-range)#^Z
SW-2#
SW-2#show ip int b
*Oct 27 22:59:21.935: %SYS-5-CONFIG_I: Configured from console by consoleri
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 unassigned YES unset up up
GigabitEthernet0/1 unassigned YES unset up up
GigabitEthernet0/2 unassigned YES unset up up
GigabitEthernet0/3 unassigned YES unset up up
Port-channel1 unassigned YES unset down down <<<<<<<<
SW-2#
Correct answer is option option C DISABLED
Question 6
mmm opcion D is a mode for PAgP, Im not sure about this question,
PAgP modes are:
On
Desirable
Auto
Off
On is a LACP modes too. So I think the question is based on the most important state for etherchannel protocols
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