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Juniper · Junos OS

Junos LACP Troubleshooting and AE Member Commands

Quick answer #

Use show lacp interfaces ae0 to inspect member negotiation, then show lacp statistics interfaces ae0 to check protocol exchanges. Also inspect the physical members. An aggregate can remain up after losing a member, so the bundle's up/down state is not a capacity check.

Scope: Junos OS aggregated Ethernet on MX and supported EX/QFX. Extensive LACP output is documented from 16.1R1. SRX reth/chassis-cluster behavior is separate; an AE example must not be treated as a reth recovery procedure.

Commands #

Read-only operational commands; replace the aggregate and member names:

Commands
Junos OS · Operational CLI

Read-only

Replace these example values: ae0.

show interfaces ae0 terse
Read-only

Replace these example values: ae0.

show lacp interfaces ae0
Read-only

Replace these example values: ae0.

show lacp interfaces ae0 extensive
Read-only

Replace these example values: ae0.

show lacp statistics interfaces ae0
Read-only

Replace these example values: xe-0/0/0.

show interfaces xe-0/0/0 extensive
Read-only

Replace these example values: xe-0/0/1.

show interfaces xe-0/0/1 extensive
Read-only

Replace these example values: ae0.

show configuration interfaces ae0 | display set
Output may contain sensitive operational data.

On older releases that do not offer extensive, use the base LACP output. Do not interpret a message that LACP is not needed by the configuration as proof of hardware failure; the bundle might be configured without LACP.

Interpret actor and partner state #

Actor describes the local participant; partner describes the remote participant. A member participating in normal bidirectional forwarding should have the appropriate synchronized, collecting and distributing state. Physical carrier alone does not establish those conditions.

Defaulted or expired partner state directs attention to protocol exchange. Compare received and transmitted LACP counters across two observations. If transmission increases but reception does not, investigate the peer configuration and the path rather than immediately replacing every local member.

Compare partner system identifiers across members of the same intended bundle. An unexpected partner can reveal incorrect cabling or a mismatch in how the far end presents its logical system. Record the actual identifiers before moving cables.

Workflow #

List the expected members and note which are physically up. Check LACP state for each one, then inspect optical/error evidence on the suspect member. Compare actor/partner data with the far-end operator. Finally verify that the aggregate has its expected capacity and that service traffic works across the intended VLANs or routed units.

Use a representative application test, but keep its limits clear. One flow does not demonstrate the total capacity of a multi-link aggregate, and unequal member byte counters alone do not establish a fault. The distribution depends on the device's forwarding and hashing configuration.

Pitfalls #

Do not bounce ae0 to diagnose one suspicious cable. Avoid changing LACP mode or minimum-links during evidence collection. Both ends must agree on bundle membership and service configuration. SRX redundant Ethernet and multi-chassis designs add dependencies that are outside this simple AE workflow; investigate their cluster or peer-control state separately.

Continue with #

Junos Interface Errors and Optical Power Commands checks each physical member and Junos LLDP, ARP and MAC Address Lookup Commands verifies neighboring ports. Junos Logs, NTP and System Health Commands helps correlate member transitions with system events. The bandwidth tool helps express the expected aggregate rate, but does not predict per-flow throughput.

Sources

Documentation reviewed: 8 October 2026