Junos Troubleshooting: 10 Essential Operational Commands

When a Juniper device starts misbehaving, the fastest path to the root cause is usually a handful of well-chosen operational commands rather than a deep dive into logs. These ten Junos tips, collected from a technical account director who supports enterprise and campus networks daily, cover the scenarios that account for most unexpected issues: power events, virtual chassis problems, cooling and hardware alarms, and interface or LACP faults. All commands work across the EX, QFX and MX families.

1. Show System Uptime

show system uptime reveals whether the device recently power-cycled — in stable enterprise networks, unexpected issues are often caused by someone knocking a power cable while working in the rack.

2. Show Virtual-Chassis Status

show virtual-chassis status verifies that every switch in an EX/QFX Virtual Chassis is present and operating. Any member shown as Not Present needs immediate investigation.

3. Show Log Messages | Last 10

show log messages | last 10 surfaces the most recent syslog entries; pipe through match to filter keywords such as link down or chassis.

4-6. Chassis Environment and Alarms

show chassis environment reports temperatures, power and fan state — fans spinning at high speed usually mean insufficient cooling. show chassis alarms covers hardware alarms (power supply, fans), while show system alarms covers software issues such as an expired UTM license or a missing rescue configuration.

7-8. Interface and LACP Checks

show interfaces descriptions | match down
show lacp interfaces

If you maintain descriptions on important uplinks, the first command highlights any important interface that is down. show lacp interfaces identifies redundant links in a LAG bundle that are down when they should be up.

9-10. Switching Table and Interface Details

show ethernet-switching table
show interfaces ge-0/0/1

In L2 environments, the switching table shows whether the switch has learned MAC addresses on a port and in which VLAN. Finally, show interfaces returns last flapped timestamps and input/output PPS rates — a healthy output rate with zero input on a WAN link points at the provider.

Related Junos articles: troubleshooting IRB VLAN interfaces on EX, inter-VLAN communication on EX switches, and SRX device upgrade steps.

原文链接：https://www.nomios.com/news-blog/ten-tips-junos-troubleshooting/