Junos Interface Errors and Optical Power Commands

Commands #

Operational mode (>), one command at a time:

show interfaces terse

show interfaces descriptions

show interfaces xe-0/0/0 extensive

show interfaces diagnostics optics xe-0/0/0

On EX/QFX, use the same optics command with the actual physical interface, for example ge-0/0/1. Do not add the logical unit .0 to an optical-module lookup. SRX has a separate optics reference and hardware support matrix; the MX field list is not a promise of SRX output.

Read the output #

Administrative state describes whether configuration enables the interface. Link state describes whether the physical connection is operational. The logical interface can have its own state and protocol configuration, so a physical link being up does not establish VLAN or IP correctness.

Record error counters twice with a known interval. A large historical count is less useful than an increase during the reported fault. Carrier transitions and the last flap time help correlate a complaint with a link interruption. Queue drops require a different investigation from physical-layer errors; avoid treating every nonzero field as a bad fiber.

Optical receive power is a measurement at this end. Compare it with that receiver's limits and, when possible, the opposite transmitter's reading. A negative dBm value is normal for many working links. There is no single healthy receive-power threshold for every transceiver. Some modules omit diagnostics, and multi-lane optics can report individual lanes.

A useful five-minute workflow #

Identify the circuit from the description and the neighboring device. Save the first interface and optics readings. Repeat the interface check while the customer reproduces the problem. Obtain the far-end readings using the same timestamps. Only then decide whether to investigate the optical path, congestion, or a higher-layer configuration.

Common mistakes #

Do not reset counters before saving evidence. An optical alarm is an investigation lead, not proof that the module itself is defective. Keep photographs, patch-panel identifiers and both-end measurements together when a physical intervention is needed. If the port belongs to ae0, inspect the member and the aggregate separately; aggregate availability can hide one failed member.

Continue with #

Use Junos LACP Troubleshooting and AE Member Commands for LACP members, Junos LLDP, ARP and MAC Address Lookup Commands to locate the peer, and Junos Logs, NTP and System Health Commands to align timestamps. The optical-power and link-budget tools help compare measurements, but do not replace the optic's specification.