portchannelGlobal Config

feature lacp

Enables Link Aggregation Control Protocol (LACP) on the switch to allow dynamic formation of port channels.

Overview

The 'feature lacp' command is used to enable the Link Aggregation Control Protocol (LACP) on Cisco NX-OS devices. LACP is an IEEE 802.3ad standard that allows the automatic bundling of multiple physical Ethernet links into a single logical link, known as a port channel or EtherChannel. This provides increased bandwidth, load balancing, and link redundancy. Without enabling this feature, LACP cannot be configured on interfaces. On NX-OS, LACP is disabled by default, unlike some other platforms. The command is entered in global configuration mode and takes no parameters. Once enabled, you can configure LACP on individual interfaces using the 'channel-group' command with modes 'active' or 'passive'. The 'active' mode initiates LACP negotiations, while 'passive' only responds. Typically, at least one side must be active. LACP is preferred over static port channels because it dynamically detects misconfigurations and adjusts to changes. In troubleshooting workflows, verifying that LACP is enabled is the first step when port channels are not forming. The 'show feature' command confirms the status. LACP also supports additional features like LACP fast rate (1-second intervals) and LACP system priority for determining which switch controls the port channel. On NX-OS, LACP is the only link aggregation protocol supported; PAgP is not available. This command is essential for any network design requiring dynamic link aggregation.

Syntax·Global Config

feature lacp

When to Use This Command

Enable LACP to dynamically bundle multiple physical links into a single logical port channel for increased bandwidth and redundancy.
Use LACP to negotiate port channel parameters automatically with a peer switch, reducing manual configuration errors.
Enable LACP when connecting to servers or switches that support LACP for standardized link aggregation.
Use LACP to facilitate load balancing across multiple links in a port channel.

Parameters

Parameter	Syntax	Required	Description
No parameters	feature lacp	Required	The command has no parameters. It simply enables the LACP feature globally on the switch.

Command Examples

Enable LACP Feature

configure terminal
feature lacp

switch(config)# feature lacp
switch(config)#

The command enables the LACP feature globally. No output indicates success. After this, LACP can be configured on interfaces.

Verify LACP Feature Status

show feature | include lacp

lacp                  1          enabled

The output shows that the LACP feature is enabled (1=enabled). If disabled, it would show '0' and 'disabled'.

Understanding the Output

The 'feature lacp' command itself does not produce output; it simply enables the feature. To verify, use 'show feature | include lacp'. The output shows the feature name, instance number, and state (enabled/disabled). A healthy state is 'enabled'. If LACP is not enabled, port channels will not form dynamically. After enabling, you must configure LACP on interfaces with 'channel-group <number> mode active' or 'passive'.

Configuration Scenarios

Basic LACP Port Channel Configuration

Two Nexus switches are connected via four 10G interfaces. We want to bundle them into a single port channel using LACP.

Topology

[Nexus-A]---(Eth1/1-4)---[Nexus-B]

Steps

1.Enable LACP feature on both switches.
2.Configure port channel interface with a channel-group number.
3.Assign physical interfaces to the port channel with LACP active mode.
4.Verify the port channel is up.

Configuration

! On Nexus-A
configure terminal
feature lacp
interface port-channel 10
  no switchport
  ip address 10.1.1.1/30
interface ethernet 1/1-4
  channel-group 10 mode active
  no shutdown

! On Nexus-B
configure terminal
feature lacp
interface port-channel 10
  no switchport
  ip address 10.1.1.2/30
interface ethernet 1/1-4
  channel-group 10 mode active
  no shutdown

Verify: show port-channel summary show lacp neighbor

Watch out: Ensure both sides have the same port channel number and LACP mode (active/active or active/passive). Mismatched modes can cause negotiation failure.

Troubleshooting with This Command

When troubleshooting LACP on NX-OS, start by verifying that the LACP feature is enabled with 'show feature | include lacp'. If disabled, enable it. Next, check the port channel status with 'show port-channel summary'. Look for the port channel to be in a 'P' (up) state. If it shows 'D' (down) or 'S' (suspended), check individual member interfaces. Use 'show lacp neighbor' to see if LACP packets are being exchanged. The output should show the neighbor's system ID and port information. If no neighbors are seen, check interface status with 'show interface ethernet X/Y'. Ensure interfaces are not err-disabled or administratively down. Also verify that the channel-group mode is consistent: at least one side must be 'active'. If the port channel is not forming, check for mismatched parameters like speed, duplex, or VLAN configuration. Use 'show lacp counters' to see LACP packet statistics; increasing 'LACPDUs Sent' but no 'LACPDUs Received' indicates a Layer 1 or 2 issue. On NX-OS, LACP uses the system MAC address as the default system ID; you can change the system priority with 'lacp system-priority'. If the port channel is up but not passing traffic, check the port channel interface configuration (e.g., IP address, VLAN membership). Also ensure that load balancing method is appropriate; use 'show port-channel load-balance' to verify. Finally, check for any hardware or software issues with 'show logging last 10' or 'show system internal lacp event-history'. Remember that LACP must be enabled on both sides for dynamic negotiation to work.

CCNA Exam Tips

Remember that 'feature lacp' is required before any LACP configuration on NX-OS.

LACP modes: active (sends LACP PDUs) and passive (responds only). Active is typically used on switches.

On NX-OS, LACP is not enabled by default; you must explicitly enable it.

Common Mistakes

Forgetting to enable 'feature lacp' before configuring LACP on interfaces, resulting in errors.

Confusing LACP with PAgP (Cisco proprietary); NX-OS supports LACP only.

Not saving the configuration after enabling the feature; it is lost on reload.

Platform Notes

On Cisco NX-OS, LACP is the only link aggregation protocol supported; PAgP (Cisco proprietary) is not available. This differs from Cisco IOS, which supports both. The 'feature lacp' command is required before any LACP configuration, whereas on IOS, LACP is available by default. On NX-OS, the command is 'feature lacp' in global config; on IOS, you configure LACP directly on interfaces without a global feature command. Additionally, NX-OS uses the 'channel-group' command with 'mode active/passive' similar to IOS, but NX-OS also supports 'mode on' for static port channels (without LACP). The 'show lacp neighbor' output on NX-OS is similar to IOS but may have slightly different formatting. On NX-OS, LACP supports up to 16 interfaces per port channel (8 active, 8 standby) with the 'lacp max-bundle' command. Also, NX-OS has a 'lacp rate' command to set fast or slow rate. In terms of version differences, NX-OS 5.x and later support LACP; earlier versions may have limited support. Always check the specific NX-OS version documentation for any caveats.

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