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Difficulty: HardLayer 2 and Layer 3 EtherChannel (LACP)

A network engineer is configuring a routed (Layer 3) EtherChannel between Switch-A and Switch-B using LACP.

Switch-A is configured with the following commands:
text
interface Port-channel 1
no switchport
ip address 10.1.1.1 255.255.255.252
!
interface range GigabitEthernet1/0/1 - 2
no switchport
channel-group 1 mode passive

When verifying the EtherChannel status on Switch-B, the engineer observes the following output from `show etherchannel summary`:
text
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
R - Layer3 S - Layer2
U - in use

Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SD) LACP Gi1/0/1(D) Gi1/0/2(D)

Which configuration change on Switch-B will successfully resolve the issue and convert Port-channel 1 into an operational Layer 3 link?

  1. Configure 'no switchport' under interface Port-channel 1 and member interfaces GigabitEthernet1/0/1 - 2, and set 'channel-group 1 mode active' on the member interfaces.Answer
  2. B
    Configure 'no switchport' under interface Port-channel 1 and member interfaces GigabitEthernet1/0/1 - 2, and set 'channel-group 1 mode passive' on the member interfaces.
  3. C
    Set 'switchport trunk native vlan 10' under interface Port-channel 1 and set 'channel-group 1 mode active' on member interfaces GigabitEthernet1/0/1 - 2.
  4. D
    Configure 'no switchport' under interface Port-channel 1 and set 'channel-group 1 mode desirable' on member interfaces GigabitEthernet1/0/1 - 2.

Answer

Configure 'no switchport' under interface Port-channel 1 and member interfaces GigabitEthernet1/0/1 - 2, and set 'channel-group 1 mode active' on the member interfaces.
To create a Layer 3 EtherChannel, the 'no switchport' command must be executed on the logical Port-channel interface as well as all physical member interfaces. Furthermore, because Switch-A is configured in LACP passive mode, Switch-B must be configured in LACP active mode ('channel-group 1 mode active') so that LACP control packets are actively sent to initiate port bundling.

Step-by-Step Solution

1
Analyze the 'show etherchannel summary' output on Switch-B.
The flags show Po1(SD) and member interfaces Gi1/0/1(D) Gi1/0/2(D). 'S' indicates Layer 2 operational state, and 'D' indicates Down state.
Layer 3 EtherChannels require explicit conversion using the 'no switchport' command on both the Port-channel logical interface and the physical member interfaces.
2
Evaluate the LACP negotiation mode requirements.
Switch-A is configured with 'channel-group 1 mode passive'.
LACP requires at least one participating switch to be in 'active' mode. Passive-to-passive mode matching will never initiate LACP control traffic, keeping the bundle down.
3
Determine the necessary configuration on Switch-B.
Apply 'no switchport' to interface Port-channel 1 and member interfaces, then assign 'channel-group 1 mode active' to member interfaces.
This establishes a Layer 3 interface ('R' flag) and enables LACP active negotiation to complement Switch-A's passive mode.

Key Concept

Layer 3 EtherChannel LACP Negotiation and CLI State Verification
Estimated Time:2m 0s
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Topics

Layer 2 and Layer 3 EtherChannel (LACP)

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