show lacp neighbor
Displays detailed LACP neighbor information for all port-channels or a specified interface, including partner system ID, port, and LACP state.
Overview
The 'show lacp neighbor' command is a vital diagnostic tool for verifying and troubleshooting Link Aggregation Control Protocol (LACP) on Cisco Nexus switches running NX-OS. LACP, defined in IEEE 802.3ad, allows the automatic bundling of multiple physical Ethernet links into a single logical link (port-channel) to increase bandwidth and provide redundancy. This command displays the LACP neighbor state for each port-channel member link, showing both the local (Actor) and remote (Partner) system information. It is used after configuring a port-channel to confirm that LACP negotiation has completed successfully, and during troubleshooting when a port-channel fails to come up or experiences intermittent issues. On NX-OS, the command output includes flags indicating LACP mode (Active/Passive) and packet rate (Slow/Fast), along with the partner's system ID, port number, and the age of the last received LACPDU. Understanding this output is essential for network engineers to quickly identify misconfigurations, such as mismatched LACP modes, incompatible port settings, or physical layer problems. The command fits into a broader troubleshooting workflow: first, use 'show port-channel summary' to see the overall status, then 'show lacp neighbor' to inspect individual member links, and finally 'show lacp counters' to check packet statistics. On Nexus switches, LACP is enabled by default on port-channels, but the mode must be configured per interface. The command is available in EXEC mode and does not require privileged access. It is platform-specific to NX-OS; similar commands exist on IOS (e.g., 'show lacp neighbor') but with slightly different output formatting. Overall, mastering this command helps ensure robust link aggregation and rapid fault isolation in data center networks.
show lacp neighbor [interface <interface>]When to Use This Command
- Verify LACP negotiation status and partner details after configuring a port-channel.
- Troubleshoot LACP adjacency issues when a port-channel is not coming up.
- Check if the partner is in active or passive mode and if LACP packets are being exchanged.
- Monitor LACP state changes during network maintenance or link failures.
Parameters
| Parameter | Syntax | Description |
|---|---|---|
| interface | interface <interface> | Specifies a particular interface (e.g., Ethernet1/1) to display LACP neighbor information for that interface only. If omitted, the command shows all LACP neighbors on the switch. |
Command Examples
Show LACP neighbor for all port-channels
show lacp neighborFlags: S - Device is sending Slow LACPDUs F - Device is sending Fast LACPDUs.
A - Device is in Active mode P - Device is in Passive mode
Interface Role Partner Partner Partner
System ID Port Number Age
po1 Actor 00:1a:2b:3c:4d:5e 0x1 10s
Partner 00:1a:2b:3c:4d:5f 0x2 12s
po2 Actor 00:1a:2b:3c:4d:60 0x3 8s
Partner 00:1a:2b:3c:4d:61 0x4 9sThe output shows two port-channels (po1, po2). For each, it lists the Actor (local) and Partner (remote) system IDs, port numbers (in hex), and age (time since last LACPDU received). Flags indicate LACP mode and rate.
Show LACP neighbor for a specific interface
show lacp neighbor interface ethernet 1/1Flags: S - Device is sending Slow LACPDUs F - Device is sending Fast LACPDUs.
A - Device is in Active mode P - Device is in Passive mode
Interface Role Partner Partner Partner
System ID Port Number Age
Eth1/1 Actor 00:1a:2b:3c:4d:5e 0x1 10s
Partner 00:1a:2b:3c:4d:5f 0x2 12sShows LACP neighbor details for Ethernet1/1. The Actor is the local switch, Partner is the remote switch. Age indicates LACP packet freshness; if age exceeds timeout, the link may be considered down.
Understanding the Output
The 'show lacp neighbor' command output provides critical information about LACP peer relationships. The first line displays flags indicating LACP mode (Active/Passive) and rate (Slow/Fast). Each interface is listed with two rows: Actor (local) and Partner (remote). The 'System ID' is the LACP system identifier (typically the switch's MAC address). 'Port Number' is the partner's port identifier in hexadecimal. 'Age' shows the time in seconds since the last LACPDU was received from that partner. A healthy LACP neighbor will show an age less than the timeout (default 30s for slow, 3s for fast). If the age is high or increasing, it indicates packet loss or misconfiguration. The flags help identify if both sides are in Active mode (preferred) or one is Passive. If the partner is not listed, LACP is not negotiating. The output also helps verify that the correct partner is connected, especially in multi-vendor environments.
Configuration Scenarios
Verifying LACP on a New Port-Channel
A network engineer has configured a port-channel between two Nexus switches and wants to verify LACP negotiation.
Topology
[Nexus-A] -- Eth1/1, Eth1/2 -- [Nexus-B]
Both interfaces are members of port-channel 1.Steps
- 1.Configure port-channel 1 on both switches with LACP active mode.
- 2.Add interfaces Ethernet1/1 and Ethernet1/2 to port-channel 1.
- 3.Use 'show lacp neighbor' to verify both interfaces show an active LACP partner.
! On Nexus-A interface port-channel1 switchport mode trunk no shutdown interface ethernet1/1 channel-group 1 mode active no shutdown interface ethernet1/2 channel-group 1 mode active no shutdown
Verify: Run 'show lacp neighbor' and confirm that for each member interface, the Partner system ID matches Nexus-B's LACP system ID and the age is low (e.g., <10s).
Watch out: Ensure both sides use the same LACP mode (active/active or active/passive). If one side is passive and the other is also passive, LACP will not negotiate.
Troubleshooting with This Command
When a port-channel fails to come up or experiences intermittent connectivity, 'show lacp neighbor' is the first command to run after verifying physical connectivity. Start by checking if any neighbor entries appear. If no neighbors are listed for a member interface, LACP packets are not being exchanged. Possible causes include: LACP not configured on the peer, mismatched LACP modes (both passive), or a Layer 1 issue (cable, transceiver). If neighbors appear but the age is high (e.g., >30s for slow rate), LACP packets are being lost, possibly due to high link utilization, errors, or a mismatch in LACP rate (slow vs fast). The flags line shows the local LACP mode and rate; ensure the peer's flags are consistent. For example, if the local interface is in Active mode but the partner shows Passive, that is acceptable as long as the partner is sending LACPDUs. However, if both are Passive, no LACPDUs are sent. Also check the partner system ID: it should match the peer switch's LACP system identifier (usually the MAC address of the management interface or a configured system priority). If the system ID is unexpected, the link may be connected to the wrong device. On NX-OS, you can also use 'show lacp counters' to see LACPDU sent/received counts. If counters are incrementing but the neighbor age is high, there may be a software issue. Additionally, verify that the port-channel is not in a suspended state due to incompatible parameters (e.g., speed, duplex, VLAN allowed). The 'show lacp neighbor' output combined with 'show port-channel summary' provides a complete picture. In summary, this command is indispensable for isolating LACP negotiation problems and ensuring stable link aggregation.
CCNA Exam Tips
Remember that LACP must be in Active mode on at least one side to initiate negotiation; Passive mode only responds.
The 'Age' field is critical for troubleshooting: if it exceeds the timeout, the port-channel may go down.
In CCNP exams, be able to interpret the flags and identify mismatched LACP modes or rates.
Common Mistakes
Confusing Actor and Partner roles; Actor is always the local device.
Assuming a missing neighbor entry means the link is down; it could also indicate LACP is not configured on the peer.
Overlooking the 'Age' field; a stale age indicates LACP communication issues.
Platform Notes
On Cisco NX-OS, the 'show lacp neighbor' command output is similar to Cisco IOS but with some differences. NX-OS includes flags for LACP mode and rate in the header, whereas IOS may display them per interface. The 'Age' field in NX-OS is in seconds; IOS may show it in a different format. NX-OS also supports the 'interface' parameter to filter output, which is also available in IOS. On other platforms like Arista EOS, the equivalent command is 'show lacp neighbor' with similar output. On Juniper Junos, the command is 'show lacp interfaces' with different formatting. For Cisco IOS-XE, the command is identical to NX-OS but may have additional fields like 'Port State'. NX-OS also supports 'show lacp system-identifier' to view the local LACP system ID, which is useful for cross-referencing with neighbor output. In terms of version differences, NX-OS 7.x and later have consistent output; earlier versions may have slight variations in flag representation. Always refer to the specific NX-OS documentation for your version. Overall, the command is a standard LACP troubleshooting tool across Cisco platforms with minor cosmetic differences.
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