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Layer 2 and Layer 3 EtherChannel (LACP)

49 questions

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Question 1Question →

A network administrator is connecting two Cisco Catalyst switches via a multi-link bundle using Link Aggregation Control Protocol (LACP). Which two conditions or configuration settings are required for the EtherChannel bundle to form and operate correctly? (Select two.)

Select all that apply

Show answer & explanation

Answer: At least one of the switches must have its physical member interfaces configured in LACP active mode.; All physical member interfaces in the bundle must be configured with identical speed, duplex, and VLAN settings.

Answer

The EtherChannel bundle successfully forms when at least one side is configured in LACP active mode and all member interfaces share matching operational parameters such as speed, duplex, and VLAN configurations.
For an LACP EtherChannel to form, at least one endpoint must actively send LACP packets (active mode), allowing negotiation when paired with an active or passive remote interface. Additionally, all bundled physical interfaces must have identical speed, duplex, switchport mode, native VLAN, and allowed VLAN attributes.

Step-by-Step Solution

1
Analyze LACP negotiation modes
LACP modes must be compatible (active-active or active-passive). Matching passive-passive modes will fail to initiate negotiation.
Passive mode only responds to LACP packets received; if neither end initiates, no negotiation occurs.
2
Evaluate member interface attribute requirements
All member links must match speed, duplex, trunking status, allowed VLANs, and native VLAN.
EtherChannel treats bundled physical links as a single logical interface, requiring identical physical and Layer 2 properties.

Key Concept

LACP Mode Compatibility and Prerequisite Interface Matching for EtherChannel
Question 2Question →

An engineer is attempting to deploy a routed Layer 3 EtherChannel between two distribution switches. The logical interface `Port-channel 1` has been configured with `no switchport` and assigned an IPv4 address. However, executing `show etherchannel summary` reveals the following output:

text
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator

Group Port-channel Protocol Ports
------+-------------+----------+-----------------------------------------------
1 Po1(SD) LACP Gi0/1(I) Gi0/2(I)

Which configuration step is required on the local switch to resolve this issue and bring the EtherChannel to an operational `SU` state?

Show answer & explanation

Answer: Execute the `no switchport` command on physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2 before bundling them into the channel group.

Answer

Execute the `no switchport` command on physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2 before bundling them into the channel group.
In Cisco IOS/IOS-XE, creating a routed (Layer 3) EtherChannel requires disabling Layer 2 switching capabilities using `no switchport` on both the physical member interfaces (GigabitEthernet0/1 and GigabitEthernet0/2) and the logical Port-Channel interface. When physical ports remain configured as Layer 2 switchports while the port-channel is routed, the physical ports cannot be bundled, showing flag `I` (stand-alone), and the port-channel shows flag `S` (Layer 2) and `D` (Down).

Step-by-Step Solution

1
Analyze the `show etherchannel summary` flags
Po1 status is `SD` (Layer 2, Down) and member ports Gi0/1 and Gi0/2 are marked with flag `I` (Stand-alone).
The flag `S` indicates the port-channel is operating in Layer 2 mode instead of Layer 3 (`R`), causing a capability mismatch with the Layer 3 logical interface setup.
2
Identify missing physical interface commands
The physical member interfaces Gi0/1 and Gi0/2 still have default Layer 2 `switchport` operational characteristics.
For a routed Layer 3 EtherChannel, `no switchport` must be applied to all participating physical member interfaces as well as the logical Port-Channel interface.
3
Determine the corrective configuration change
Entering interface range configuration mode for Gi0/1 - 2 and issuing `no switchport` converts the physical member interfaces to Layer 3, allowing them to successfully bundle (`P`) under `Po1(RU)`.
Layer matching across physical member ports and logical channel interfaces is mandatory for successful LACP aggregation.

Key Concept

Layer 3 EtherChannel Physical and Logical Port Matching
Question 3Question →

A network administrator is connecting two Cisco Catalyst switches using an IEEE 802.3ad Link Aggregation Control Protocol (LACP) EtherChannel. SwitchA has its member interfaces configured with the command `channel-group 1 mode passive`. Which mode must be configured on SwitchB's corresponding member interfaces to successfully form the EtherChannel?

Show answer & explanation

Answer: active

Answer

The mode 'active' must be configured on SwitchB.
The correct answer specifies 'active' mode. In LACP, 'active' mode actively sends LACP negotiation frames, whereas 'passive' mode only listens and responds. Because the remote switch is set to 'passive', the local switch must be set to 'active' to initiate communication and successfully build the bundle.

Step-by-Step Solution

1
Identify the protocol associated with the configured mode.
The command 'mode passive' indicates the use of Link Aggregation Control Protocol (LACP), an open standard protocol.
EtherChannel negotiation protocols (LACP vs PAgP) cannot be mixed.
2
Analyze the operational state of LACP 'passive' mode on SwitchA.
SwitchA is in a passive state, meaning it will listen and respond to incoming LACP packets but will not initiate negotiation.
Two passive switches will wait indefinitely for the other to start negotiation, keeping the link down.
3
Determine the required mode for SwitchB.
SwitchB must be set to 'active' mode so that it actively transmits LACP packets to initiate channel creation.
An LACP EtherChannel requires at least one side to actively initiate negotiation (active-active or active-passive).

Key Concept

LACP Mode Compatibility
Question 4Question →

A network engineer needs to build a functional Layer 3 LACP EtherChannel (Port-channel 10) between two Cisco Catalyst switches using interfaces GigabitEthernet1/0/1 and GigabitEthernet1/0/2. Place the required Cisco IOS CLI configuration steps in the correct order from start to finish.

Drag items to arrange them in the correct order

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Answer

The correct sequence for configuring a Layer 3 LACP EtherChannel is: first select the physical interface range (`interface range GigabitEthernet1/0/1 - 2`), disable Layer 2 switching on the physical ports (`no switchport`), create/assign the LACP active group (`channel-group 10 mode active`), enter the logical port-channel interface (`interface Port-channel 10`), and finally assign the IPv4 address (`ip address 192.168.10.1 255.255.255.252`).
To successfully configure a Layer 3 EtherChannel, physical member links must first be selected and converted into routed ports via the `no switchport` command. Next, the LACP dynamic protocol mode (`mode active`) is applied to bind the physical interfaces into channel-group 10. Finally, the network administrator enters the logical `interface Port-channel 10` configuration mode and assigns the IP address to the aggregate interface.

Step-by-Step Solution

1
Select physical range
Enters range configuration mode `(config-if-range)` for member ports.
Allows simultaneous configuration of physical interfaces GigabitEthernet1/0/1 and GigabitEthernet1/0/2.
2
Execute `no switchport` on physical links
Member interfaces become routed ports.
Physical ports must be routed interfaces before being grouped into a Layer 3 EtherChannel.
3
Execute `channel-group 10 mode active`
Creates logical interface Port-channel 10 and binds member links using LACP.
The `active` keyword initiates LACP negotiation.
4
Enter `interface Port-channel 10`
Enters interface configuration mode `(config-if)` for the logical bundle.
Layer 3 parameters must be configured on the aggregate port-channel interface.
5
Assign IP address with `ip address 192.168.10.1 255.255.255.252`
Port-channel 10 is configured with a unicast IP address.
Completes Layer 3 routed EtherChannel setup.

Key Concept

Layer 3 EtherChannel Configuration Sequence
Question 5Question →

A network administrator needs to aggregate physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2 into a Layer 3 LACP EtherChannel (Port-channel 1) and assign an IP address of 10.1.1.1/30 to the logical interface. Place the configuration steps in the correct sequential order from first to last.

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Answer

The correct configuration order is: 1) Select physical member ports (interface range GigabitEthernet0/1 - 2), 2) Disable Layer 2 switching (no switchport), 3) Associate ports with LACP channel-group (channel-group 1 mode active), 4) Enter logical port-channel mode (interface Port-channel 1), and 5) Assign the IP address (ip address 10.1.1.1 255.255.255.252).
To successfully configure a Layer 3 EtherChannel using LACP, physical member interfaces must first be selected (`interface range`), converted to routed ports (`no switchport`), and joined to an active LACP channel group (`channel-group 1 mode active`). Afterwards, the logical interface context must be accessed (`interface Port-channel 1`) to assign the designated IP address (`ip address 10.1.1.1 255.255.255.252`).

Step-by-Step Solution

1
Select target physical interfaces
System enters interface range configuration mode prompt switch(config-if-range)#
Configuration commands must target both physical member interfaces simultaneously.
2
Execute 'no switchport' on physical member interfaces
Physical ports are converted from Layer 2 switch ports to Layer 3 routed ports
Layer 3 EtherChannels require member interfaces to operate in routed mode.
3
Execute 'channel-group 1 mode active'
Physical interfaces are added to EtherChannel group 1 using LACP active negotiation, creating Port-channel 1
The 'active' keyword enables dynamic IEEE 802.3ad LACP protocol negotiation.
4
Execute 'interface Port-channel 1'
System enters interface configuration mode for the logical port-channel switch(config-if)#
Layer 3 IP attributes must be applied directly to the logical bundled interface.
5
Execute 'ip address 10.1.1.1 255.255.255.252'
Logical interface Port-channel 1 receives the specified IP address and subnet mask
This enables routing over the aggregated logical EtherChannel link.

Key Concept

Layer 3 EtherChannel Configuration with LACP
Question 6Question →

SwitchA has its interconnecting physical interfaces configured with the command `channel-group 1 mode passive`. Which channel-group mode must be configured on SwitchB for the IEEE 802.3ad LACP EtherChannel to successfully form?

Show answer & explanation

Answer: `active`

Answer

The mode configured on SwitchB must be `active`.
The `active` mode causes the switch port to actively initiate negotiations by sending LACP frames. Since SwitchA is configured as `passive`, it only responds to received LACP frames. SwitchB must be in `active` mode so LACP frames are transmitted to start the dynamic trunk negotiation.

Step-by-Step Solution

1
Analyze the LACP mode configured on SwitchA.
SwitchA is set to `passive`, meaning it responds to LACP packets but will not initiate LACP frame exchanges.
LACP passive mode requires an incoming LACP negotiation request to begin bundling interfaces.
2
Determine the compatible LACP mode required on SwitchB.
SwitchB must be set to `active` so that it actively transmits LACP control frames to SwitchA.
At least one end of an LACP EtherChannel link must be in `active` mode for successful negotiation.

Key Concept

LACP Mode Compatibility
Question 7Question →

A network administrator needs to configure a routed (Layer 3) LACP EtherChannel (Port-Channel 10) using physical member interfaces GigabitEthernet0/1 and GigabitEthernet0/2, and assign the IPv4 address 10.1.1.1/30 to the bundle. Place the CLI configuration steps in the correct operational sequence from first to last.

Drag items to arrange them in the correct order

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Answer

The correct configuration sequence is: First select physical interfaces with `interface range GigabitEthernet0/1 - 2`, second disable Layer 2 operation using `no switchport`, third associate member interfaces into LACP using `channel-group 10 mode active`, fourth enter logical interface mode via `interface Port-channel10`, and fifth configure the IPv4 address using `ip address 10.1.1.1 255.255.255.252`.
The correct operational sequence begins by selecting physical interfaces using `interface range GigabitEthernet0/1 - 2`, converting them to routed interfaces with `no switchport`, and binding them to the dynamic LACP channel group via `channel-group 10 mode active`. Next, configuration mode shifts to the created virtual interface using `interface Port-channel10`, where the IP address is configured with `ip address 10.1.1.1 255.255.255.252`.

Step-by-Step Solution

1
Select physical interfaces
Enters interface range configuration mode for GigabitEthernet0/1 and GigabitEthernet0/2.
Configuration options must be applied to physical interfaces simultaneously using interface range mode.
2
Convert interfaces to Layer 3
Removes switchport capabilities from member interfaces.
Physical member ports must be converted to routed ports with `no switchport` prior to creating a Layer 3 EtherChannel.
3
Configure LACP channel group
Creates Port-channel10 and enables active dynamic negotiation.
Executing `channel-group 10 mode active` dynamically creates the Port-channel interface using LACP.
4
Enter logical Port-Channel interface
Transitions CLI prompt to `config-if` mode for Port-channel10.
Network layer configuration parameters must be applied to the virtual interface rather than physical ports.
5
Assign IPv4 addressing
Applies IP subnet 10.1.1.1/30 to the EtherChannel logical interface.
Layer 3 EtherChannels route traffic based on the IP address assigned directly to the Port-Channel interface.

Key Concept

Layer 3 EtherChannel (LACP) CLI Configuration Sequence
Estimated Time:1m 30s
Question 8Question →

Two Cisco switches, Switch-A and Switch-B, are linked using physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2. The network team intends to aggregate these links using dynamic trunk negotiation. A technician executes `channel-group 5 mode active` on Switch-A's physical interfaces, but configures `channel-group 5 mode desirable` on Switch-B's physical interfaces.

After applying these configurations, the output of `show etherchannel summary` on Switch-A indicates a status of `Po5(SD)` with member ports showing `(D)`. Which explanation correctly accounts for this operational failure?

Show answer & explanation

Answer: LACP and PAgP are distinct negotiation protocols, causing channel negotiation to fail when combining `active` (LACP) with `desirable` (PAgP).

Answer

LACP and PAgP are distinct negotiation protocols, causing channel negotiation to fail when combining active (LACP) with desirable (PAgP).
EtherChannel links require matching protocols on both ends. Mode `active` triggers dynamic negotiation using LACP (IEEE 802.3ad), while mode `desirable` triggers dynamic negotiation using PAgP (Cisco proprietary). Because LACP and PAgP packets are incompatible, the switches cannot complete handshaking, causing the port-channel to remain down `Po5(SD)` with physical interfaces down `(D)` or standalone.

Step-by-Step Solution

1
Identify the protocol associated with each channel-group mode.
Mode `active` utilizes IEEE 802.3ad LACP, whereas mode `desirable` utilizes Cisco proprietary PAgP.
EtherChannel negotiation protocols must match on both ends of the link.
2
Analyze protocol compatibility between Switch-A and Switch-B.
Switch-A transmits LACP PDUs while Switch-B transmits PAgP packets. Neither switch understands the other's control frames.
LACP and PAgP cannot interoperate or establish a negotiated bundle.
3
Correlate protocol mismatch with CLI verification status `Po5(SD)`.
The Port-channel remains down (D) at Layer 2 (S) because dynamic negotiation fails completely.
Without successful negotiation, physical ports are kept in a down or unbundled state to prevent layer 2 loops.

Key Concept

EtherChannel Protocol and Mode Compatibility (LACP vs PAgP)
Question 9Question →

Two Cisco switches, SW1 and SW2, are interconnected using three physical links: GigabitEthernet1/0/1, GigabitEthernet1/0/2, and GigabitEthernet1/0/3. An engineer attempts to aggregate all three links into a routed Layer 3 EtherChannel (Port-channel 12).

On SW1, the engineer configures `no switchport` on `interface Port-channel 12` along with IPv4 addressing, and assigns all three physical interfaces using `channel-group 12 mode active`.

On SW2, `no switchport` and IP addressing are configured on `interface Port-channel 12`. Interfaces GigabitEthernet1/0/1 and GigabitEthernet1/0/2 are configured with `channel-group 12 mode passive`, while interface GigabitEthernet1/0/3 is configured with `channel-group 12 mode auto`.

Upon checking operational status, Port-channel 12 is up with IPv4 connectivity, but only GigabitEthernet1/0/1 and GigabitEthernet1/0/2 are bundled (`P` flag in `show etherchannel summary`), whereas GigabitEthernet1/0/3 remains unbundled (`I` flag on SW1 and `D` flag on SW2).

Which condition correctly explains why interface GigabitEthernet1/0/3 failed to join the EtherChannel bundle?

Show answer & explanation

Answer: Interface GigabitEthernet1/0/3 on SW2 is configured with PAgP mode auto, which cannot negotiate an EtherChannel bundle with SW1's LACP mode active.

Answer

Interface GigabitEthernet1/0/3 on SW2 is configured with PAgP mode auto, which cannot negotiate an EtherChannel bundle with SW1's LACP mode active.
The root cause of the bundling failure on GigabitEthernet1/0/3 is a protocol mismatch. SW1 is configured with LACP (`channel-group 12 mode active`), while SW2's GigabitEthernet1/0/3 is configured with PAgP (`channel-group 12 mode auto`). Because IEEE 802.3ad LACP and Cisco proprietary PAgP speak completely different protocol languages, negotiation fails and the link drops out of the bundle, showing standalone (`I`) or down (`D`) flags.

Step-by-Step Solution

1
Analyze negotiation protocol assignment on SW1.
SW1 uses `channel-group 12 mode active` across all three physical interfaces, designating LACP (IEEE 802.3ad) as the aggregation control protocol.
The `active` keyword explicitly enables LACP and actively sends LACP PDUs.
2
Analyze negotiation protocol assignment on SW2 member interfaces.
Interfaces Gig1/0/1 and Gig1/0/2 use `passive` (LACP), whereas Gig1/0/3 uses `auto` (PAgP).
The `auto` keyword enables Cisco proprietary PAgP, which expects PAgP packets (`desirable` or `auto`), not LACP PDUs.
3
Evaluate protocol compatibility for GigabitEthernet1/0/3.
SW1 sends LACP PDUs on Gig1/0/3, while SW2 listens for PAgP packets on Gig1/0/3. Neither switch receives compatible aggregation negotiation frames.
LACP and PAgP are incompatible protocols and cannot form an EtherChannel across opposing endpoints.

Key Concept

LACP and PAgP Mode Incompatibility in EtherChannel Aggregation
Question 10Question →

A network engineer is configuring a routed (Layer 3) EtherChannel bundle between two Cisco switches using Link Aggregation Control Protocol (LACP). Which TWO configuration steps must be performed on the physical member interfaces to correctly establish the channel?

Select all that apply

Show answer & explanation

Answer: Execute the `no switchport` command on each physical member interface.; Apply the `channel-group 1 mode active` command to the physical member interfaces.

Answer

The correct steps are executing the `no switchport` command on physical member interfaces and placing them into an active LACP mode using `channel-group 1 mode active`.
To construct a Layer 3 EtherChannel, physical member interfaces must first be converted from switchports to routed interfaces using the `no switchport` command. Next, an LACP negotiation mode (active or passive) must be configured using the `channel-group` command on those physical interfaces.

Step-by-Step Solution

1
Convert physical member interfaces to Layer 3 mode
The physical interfaces cease operating as Layer 2 switchports.
Layer 3 EtherChannels require member links to operate as routed ports.
2
Enable LACP negotiation on physical member interfaces
Physical interfaces send LACP packets to initiate bundle negotiation.
Setting the channel-group mode to active enables LACP dynamic negotiation.

Key Concept

Layer 3 LACP EtherChannel Configuration
Question 11Question →

A network administrator needs to configure a routed Layer 3 EtherChannel using LACP across physical interfaces GigabitEthernet 0/1 and 0/2 on a Cisco Catalyst switch. Drag and drop the CLI configuration steps into the correct sequential order from first to last.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence begins with selecting the physical interface range, disabling switchport functionality to convert them to Layer 3, defining the LACP channel group mode to generate the logical bundle, and finally entering the Port-channel interface to assign the IP address.
To create a functional Layer 3 EtherChannel using LACP, the network administrator must first access the physical member interfaces using the range command, disable Layer 2 switchport characteristics with 'no switchport', group the links into an active LACP channel group with 'channel-group 1 mode active', and finally apply the network IP addressing directly onto the resulting logical Port-channel interface.

Step-by-Step Solution

1
Select member physical interfaces
Enters interface range configuration mode for GigabitEthernet 0/1 - 2.
Configuration must begin on the target member links.
2
Convert physical ports to routed ports
Disables Layer 2 port capabilities using 'no switchport'.
Layer 3 EtherChannels require member ports to be routed ports prior to forming a Layer 3 logical port-channel.
3
Enable LACP dynamic negotiation
Creates Port-channel 1 and initiates active LACP negotiations via 'channel-group 1 mode active'.
The 'active' keyword explicitly selects LACP protocol for bundle aggregation.
4
Assign IP address to the Port-channel
Navigates to 'interface Port-channel 1' and configures 'ip address 10.1.1.1 255.255.255.252'.
In a Layer 3 EtherChannel, routing parameters and IP addresses reside on the logical port-channel interface, not on individual physical members.

Key Concept

Layer 3 EtherChannel LACP Configuration Sequence
Question 12Question →

A network technician is setting up dynamic link aggregation using Link Aggregation Control Protocol (LACP) between two Cisco switches. Which TWO channel-group mode pairings will successfully establish an operational EtherChannel bundle? (Select two.)

Select all that apply

Show answer & explanation

Answer: Both switch interfaces configured in active mode; One switch interface configured in active mode and the other in passive mode

Answer

The correct options are configuring both interfaces in active mode, and configuring one interface in active mode with the opposing interface in passive mode.
LACP EtherChannel formation requires at least one participating interface to be in active mode to send LACP frames. Thus, active-active and active-passive combinations will both form a functional bundle.

Step-by-Step Solution

1
Analyze LACP operational modes.
Active mode actively transmits LACP packets, whereas passive mode only responds to received LACP packets.
At least one endpoint must be configured in active mode to initiate the LACP packet exchange.
2
Evaluate protocol compatibility.
Desirable mode belongs to PAgP, which is incompatible with LACP.
Both switches must use matching aggregation protocols (LACP to LACP or PAgP to PAgP).

Key Concept

LACP Mode Negotiation Dynamics
Question 13Question →

A network engineer is deploying a point-to-point Layer 3 EtherChannel between two Cisco Catalyst switches, SW-Alpha and SW-Beta.

On SW-Alpha, the engineer issued `no switchport` on physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2, added them to `channel-group 10 mode active`, and then configured `interface Port-channel 10` with `no switchport` and IP address `10.20.30.1 255.255.255.252`.

On SW-Beta, the engineer configured `interface Port-channel 10` with `no switchport` and IP address `10.20.30.2 255.255.255.252`. Next, the physical member interfaces GigabitEthernet0/1 and GigabitEthernet0/2 were assigned to `channel-group 10 mode passive`, but the engineer omitted the `no switchport` command on those physical member interfaces.

Executing `show etherchannel summary` on SW-Beta displays the following output:

text Flags: D - down P - bundled in port-channel I - stand-alone s - suspended H - Hot-standby (LACP only) R - Layer3 S - Layer2 U - in use f - failed to allocate aggregate interface Group Port-channel Protocol Ports ------+-------------+-----------+----------------------------------------------- 10 Po10(SD) LACP Gi0/1(D) Gi0/2(D)

Which configuration oversight on SW-Beta caused Port-channel 10 to exhibit the `SD` (Layer 2, Down) status flags?

Show answer & explanation

Answer: The physical member interfaces on SW-Beta were left operating in default Layer 2 switchport mode, preventing them from joining a routed Layer 3 port-channel bundle.

Answer

The physical member interfaces on SW-Beta remained in Layer 2 switchport mode because the 'no switchport' command was omitted on GigabitEthernet0/1 and GigabitEthernet0/2.
For a Layer 3 (routed) EtherChannel to operate correctly, physical member interfaces must be explicitly configured as routed ports using the 'no switchport' command. If physical ports remain in their default Layer 2 switchport state when added to a channel group, they cannot bundle with a routed port-channel interface, resulting in the port-channel defaulting to Layer 2 Down ('SD') status and physical ports marked as Down ('D').

Step-by-Step Solution

1
Analyze the output flags of 'show etherchannel summary' on SW-Beta.
Port-channel 10 displays flags 'SD', where 'S' indicates Layer 2 (Switchport) and 'D' indicates Down. Member ports Gi0/1 and Gi0/2 are marked with flag 'D' (Down).
Understanding flag meanings allows diagnosing whether the channel is operating as Layer 2 or Layer 3 and identifying port bundling status.
2
Evaluate the configuration differences between SW-Alpha and SW-Beta.
SW-Alpha configured 'no switchport' on both physical member interfaces and the logical port-channel interface. SW-Beta configured 'no switchport' only on the logical Port-channel interface but omitted it on physical member interfaces GigabitEthernet0/1 and GigabitEthernet0/2.
On Cisco Catalyst switches, physical interfaces operate as Layer 2 switchports by default.
3
Determine the operational requirement for Layer 3 EtherChannels.
Physical member interfaces must match the Layer 2/Layer 3 capability of the logical Port-channel interface. When physical ports remain Layer 2 switchports, Cisco IOS prevents them from bundling into a routed Port-channel, driving the Port-channel interface state to Layer 2 Down ('SD').
Applying 'no switchport' to the physical member interfaces before assigning them to the channel group ensures parameter consistency and enables successful LACP bundle establishment.

Key Concept

Layer 3 EtherChannel Physical Member Interface Requirements
Estimated Time:2m 0s
Question 14Question →

A network administrator needs to convert two physical switch interfaces (GigabitEthernet0/1 and GigabitEthernet0/2) on a Cisco Catalyst switch into a routed (Layer 3) EtherChannel bundle using dynamic LACP active mode. In what sequential order should the Cisco IOS configuration commands be executed to successfully establish the routed port-channel interface and configure its IP addressing?

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct CLI configuration sequence is: enter physical interface range mode ('interface range GigabitEthernet0/1 - 2'), convert physical links to routed mode ('no switchport'), assign interfaces to dynamic LACP group ('channel-group 10 mode active'), enter logical port-channel mode ('interface Port-channel 10'), and assign the IP address ('ip address 10.10.10.1 255.255.255.252').
To build a routed (Layer 3) EtherChannel using LACP, an engineer must first enter physical interface configuration mode ('interface range GigabitEthernet0/1 - 2'), disable Layer 2 processing on those physical member links using 'no switchport', and bind them into an active LACP bundle with 'channel-group 10 mode active'. Once the bundle is formed, the engineer enters the logical interface mode ('interface Port-channel 10') and applies the IPv4 network parameters using 'ip address 10.10.10.1 255.255.255.252'.

Step-by-Step Solution

1
Select physical member interfaces using 'interface range GigabitEthernet0/1 - 2'
Enters interface range configuration mode for both physical ports simultaneously.
Configuration commands must target the physical interfaces that will compose the EtherChannel.
2
Disable Layer 2 functionality on physical links using 'no switchport'
Converts physical member interfaces from Layer 2 switchports to Layer 3 routed interfaces.
If interfaces remain in Layer 2 mode when assigned to a channel group, a Layer 2 port-channel will be created instead of a Layer 3 port-channel.
3
Bind physical interfaces into an LACP group using 'channel-group 10 mode active'
Creates logical Port-channel 10 and initiates LACP active negotiation on physical member links.
The 'active' keyword specifies dynamic LACP negotiation protocol mode.
4
Enter logical bundle interface configuration using 'interface Port-channel 10'
Moves CLI focus to the newly spawned logical interface Port-channel 10.
Layer 3 IP attributes must be configured on the parent logical bundle rather than individual member links.
5
Configure the IP address using 'ip address 10.10.10.1 255.255.255.252'
Assigns Layer 3 IPv4 addressing to Port-channel 10 for routing.
In a Layer 3 EtherChannel, routing parameters reside on the logical Port-channel interface.

Key Concept

Layer 3 LACP EtherChannel CLI Configuration Sequence
Question 15Question →

A network engineer is configuring a routed (Layer 3) EtherChannel between two switches using LACP. The engineer issued the `no switchport` command on physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2 before assigning them to channel group 1 with mode `active`. However, the bundle fails to pass routed traffic. Upon executing `show etherchannel summary`, the output displays:

text
Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SD) LACP Gi0/1(I) Gi0/2(I)

Which administrative action will resolve this issue and bring the Layer 3 EtherChannel into an operational state?

Show answer & explanation

Answer: Issue the `no switchport` command on the logical Port-Channel 1 interface.

Answer

Issue the `no switchport` command on the logical Port-Channel 1 interface.
The `show etherchannel summary` command output displays `Po1(SD)`, where `S` signifies Layer 2 and `D` signifies Down. Because the physical member interfaces were configured with `no switchport`, they are operating as Layer 3 ports. LACP prevents ports from bundling if there is a mismatch between the physical member ports and the logical port-channel interface mode. Converting the Port-Channel 1 interface to Layer 3 using `no switchport` resolves the configuration mismatch and enables the LACP bundle to become operational (`Po1(RU)` or `Po1(SU)` depending on code version definitions).

Step-by-Step Solution

1
Analyze the flags in the `show etherchannel summary` output.
Flag `S` on `Po1(SD)` indicates Layer 2 operational mode, and flag `D` indicates Down. Flags `(I)` on member ports indicate Stand-alone state.
The physical ports were configured as routed ports (`no switchport`), but the logical Port-Channel interface retained its default Layer 2 switchport property.
2
Identify the underlying compatibility requirement for EtherChannel aggregation.
All physical member interfaces and the parent Port-Channel interface must share matching operational parameters, including Layer 2 vs. Layer 3 mode.
LACP will suspend member ports or keep them stand-alone if there is a Layer 2 / Layer 3 mode mismatch with the logical port-channel.
3
Determine the corrective CLI command on the logical interface.
Executing `interface Port-channel 1` followed by `no switchport` converts the logical interface to Layer 3.
Aligning the logical interface mode to Layer 3 allows LACP to bundle Gi0/1 and Gi0/2 into Po1, changing the flags to `SU` (Layer 3, in Use) and member port flags to `P` (bundled in port-channel).

Key Concept

Layer 3 EtherChannel Configuration and Operability Flags
Estimated Time:2m 0s
Question 16Question →

An enterprise network team is troubleshooting an LACP-based routed EtherChannel between Switch-1 and Switch-2.

Switch-1 configuration snippet:
interface range GigabitEthernet0/1 - 2
no switchport
channel-group 12 mode active
!
interface Port-channel 12
no switchport
ip address 10.1.12.1 255.255.255.252

Switch-2 command output:
# show etherchannel summary
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby S - Layer2
R - Layer3 U - in use
Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
12 Po12(SD) LACP Gi0/1(I) Gi0/2(I)

Which configuration change on Switch-2 will successfully establish the Layer 3 EtherChannel and bring Port-channel 12 to the operational Layer 3 state (RU)?

Show answer & explanation

Answer: Configure 'no switchport' and 'channel-group 12 mode passive' on physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2, then assign the IP address under interface Port-channel 12.

Answer

The correct action is to configure 'no switchport' and 'channel-group 12 mode passive' on physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2, and assign the IP address under interface Port-channel 12.
To transition Port-channel 12 on Switch-2 from (SD) Layer 2 Down to (RU) Layer 3 In-Use, the physical member interfaces (Gi0/1 and Gi0/2) must have switchport functionality disabled via 'no switchport'. LACP dynamic negotiation requires compatible modes across both switches; since Switch-1 is configured in 'active' mode, Switch-2 can use either 'active' or 'passive' mode. Lastly, IP addressing in a Layer 3 EtherChannel must be assigned directly to the Port-channel 12 logical interface rather than to the individual member interfaces.

Step-by-Step Solution

1
Analyze the output of 'show etherchannel summary' on Switch-2.
Port-channel 12 shows flag 'S' (Layer 2) and 'D' (Down), while physical interfaces show 'I' (Stand-alone). Switch-1 is configured as Layer 3 ('R').
The flags indicate a Layer mismatch (Layer 2 on Switch-2 vs Layer 3 on Switch-1) and independent member states due to incomplete Layer 3/LACP setup.
2
Determine Layer 3 EtherChannel requirements for member interfaces.
Member interfaces must be routed ports using the 'no switchport' command prior to or matching port-channel settings.
EtherChannel member interfaces must match Layer 2 or Layer 3 properties to form an operational bundle.
3
Verify LACP mode compatibility.
Switch-1 is set to 'active'. Switch-2 must be set to 'active' or 'passive'.
LACP requires at least one side to be in active mode to initiate link aggregation control protocol negotiation.
4
Verify Layer 3 IP address placement.
The IP address must be assigned to interface Port-channel 12, not to individual physical interfaces.
In a routed EtherChannel, the port-channel interface acts as the single logical Layer 3 routing point.

Key Concept

Layer 3 EtherChannel LACP Negotiation and Troubleshooting
Estimated Time:3m 0s
Question 17Question →

Two Cisco Catalyst switches are connected using four physical Ethernet links intended for a high-capacity trunk bundle. The interfaces on Switch-1 are configured with `channel-group 5 mode active`, while the interfaces on Switch-2 are configured with `channel-group 5 mode passive`. After connecting the cables, three of the four links bundle successfully into `Port-channel 5`, but interface `GigabitEthernet0/1` on Switch-1 remains in an Independent (`I`) operational state. What is the primary cause of this member interface failing to join the active LACP EtherChannel?

Show answer & explanation

Answer: The interface has an operational speed or duplex setting that does not match the other physical member interfaces in the bundle.

Answer

The physical interface has an operational speed or duplex setting that does not match the other physical member interfaces in the bundle.
EtherChannel member interfaces must be configured identically regarding speed, duplex, media type, VLAN range, and trunking mode. If a single interface has a mismatched operational speed or duplex setting (e.g., auto-negotiated to 100/full instead of 1000/full), LACP consistency checks will fail for that port. Cisco IOS will flag the interface as Independent ('I') in the show etherchannel summary output, keeping it operating standalone outside the bundle while the matching ports form the EtherChannel.

Step-by-Step Solution

1
Analyze the LACP negotiation mode compatibility between Switch-1 and Switch-2.
Switch-1 is set to 'active' and Switch-2 is set to 'passive'. Active-to-passive is a valid LACP negotiation combination, so mode mismatch between switches is not the issue.
LACP active mode actively sends LACPDU packets, while passive mode responds to incoming LACPDUs.
2
Identify mandatory prerequisite physical interface matching parameters for EtherChannel member ports.
All member ports in an EtherChannel bundle must match speed, duplex, interface mode (access/trunk), native VLAN, and allowed VLANs.
If any individual physical port has a mismatched operational attribute (such as 100 Mbps when others are 1 Gbps), Cisco IOS prevents that port from joining the bundle to protect against frame misordering or forwarding loops.
3
Interpret the 'I' (Independent) flag in 'show etherchannel summary' output.
The 'I' flag indicates that the port is operating standalone (independently) because it failed EtherChannel consistency checks or negotiation.
Speed/duplex mismatch on that specific interface causes it to drop out of the logical bundle while remaining active as a standalone port.

Key Concept

EtherChannel Physical Interface Prerequisites & LACP Verification
Estimated Time:1m 15s
Question 18Question →

A network administrator is attempting to establish an operational Layer 3 EtherChannel using LACP between two Cisco switches. After applying the initial configuration, the administrator issues the `show etherchannel summary` command on Switch1 and observes the following output:

Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby s - Layer2
R - Layer3 U - in use

Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SD) LACP Gi0/1(D) Gi0/2(D)

Which configuration change on Switch1 is required to allow Port-Channel 1 to operate successfully as a Layer 3 EtherChannel?

Show answer & explanation

Answer: Configure the `no switchport` command on physical member interfaces GigabitEthernet0/1 and GigabitEthernet0/2 before adding them to the channel group.

Answer

Configure the `no switchport` command on physical member interfaces GigabitEthernet0/1 and GigabitEthernet0/2 before adding them to the channel group.
For a Layer 3 EtherChannel to operate correctly, physical member interfaces must be explicitly configured as routed ports using the `no switchport` command. The flag `S` in `Po1(SD)` indicates the interface bundle is operating at Layer 2. Converting the physical member ports to Layer 3 allows the EtherChannel to transition to the `RU` (Layer 3, in use) operational state.

Step-by-Step Solution

1
Analyze the output flags from `show etherchannel summary`.
The logical interface displays `Po1(SD)`, where `S` indicates Layer 2 operational mode and `D` indicates the channel is Down. Member interfaces display `(D)` for down.
The flag `S` indicates the physical interfaces are currently operating as Layer 2 switchports rather than Layer 3 routed ports.
2
Identify the requirement for creating a Layer 3 EtherChannel in Cisco IOS.
Both the physical member interfaces and the logical port-channel interface must be configured with `no switchport` to function as routed interfaces.
If physical interfaces remain in Layer 2 switchport mode, the port-channel cannot bundle them into a Layer 3 (`R`) operational state.
3
Determine the corrective CLI commands.
Navigate to `interface range GigabitEthernet0/1 - 2` and execute `no switchport`, then re-assign `channel-group 1 mode active`.
Disabling switchport mode allows the interfaces to negotiate as Layer 3 routed ports and transition the port-channel state flag from `SD` to `RU` (Layer 3, in use).

Key Concept

Layer 3 EtherChannel Member Configuration
Estimated Time:1m 30s
Question 19Question →

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?

Show answer & explanation

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.

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
Question 20Question →

A network engineer is configuring a Link Aggregation Control Protocol (LACP) EtherChannel between two switches. Which TWO channel-group mode combinations between the interconnected switch ports will successfully establish an operational EtherChannel bundle? (Select two.)

Select all that apply

Show answer & explanation

Answer: Active mode on the local switch port and active mode on the remote switch port; Active mode on the local switch port and passive mode on the remote switch port

Answer

The configurations that successfully form an LACP EtherChannel bundle are active-to-active and active-to-passive mode combinations.
For an IEEE 802.3ad Link Aggregation Control Protocol (LACP) EtherChannel to form, at least one interface must be set to active mode so that LACP frames are transmitted across the link. Consequently, combining an active interface with another active interface, or an active interface with a passive interface, results in a operational EtherChannel bundle.

Step-by-Step Solution

1
Analyze LACP mode behaviors
Active mode actively originates LACP negotiation frames. Passive mode only listens and responds to incoming LACP frames.
For negotiation to take place, at least one endpoint must generate negotiation frames.
2
Evaluate the mode combinations for compatibility
Active-to-active and active-to-passive form valid LACP EtherChannels. Passive-to-passive fails because neither interface transmits LACP negotiation frames. Active-to-desirable fails because LACP and PAgP are incompatible protocols.
EtherChannel negotiation protocols must match on both ends, and at least one port must actively send negotiation frames.

Key Concept

LACP EtherChannel Mode Negotiation Rules
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