Juniper JunOS Device Health Check#

Structured triage procedure for assessing Juniper device health across MX, SRX, EX, QFX, and PTX platforms. Produces a prioritized findings report with severity classifications and recommended actions.

JunOS separates Routing Engine (RE) and Packet Forwarding Engine (PFE). These are independent health domains — a healthy RE does not guarantee a healthy PFE, and vice versa. This procedure assesses both explicitly.

When to Use#

• Device reported as slow, dropping traffic, or unresponsive
• Scheduled health audit of Juniper routers, switches, or firewalls
• Post-change verification after commits, upgrades, or ISSU
• Capacity planning data collection for RE CPU, memory, and link utilization
• Incident response when a Juniper device is suspected as the fault domain
• RE failover event — verify mastership and standby RE state
• Chassis alarm triggered — severity triage and root cause identification

Prerequisites#

• SSH or console access to the device (login class with view permissions minimum)
• JunOS 21.x or later (commands validated against JunOS 23.2+)
• Network reachability to management interface or fxp0 confirmed
• Awareness of the device's normal baseline (CPU, memory, traffic patterns)
• For dual-RE systems: know which RE should be master under normal operations
• Knowledge of recent commit history if correlating symptoms with changes

Procedure#

Follow this sequence. Each step produces data for the final report. RE mastership verification is mandatory first — all subsequent data is RE-scoped.

Step 1: Verify RE Mastership (Mandatory)#

On dual-RE systems, health data comes from the RE you are logged into. If you are on the backup RE, all metrics reflect the standby engine — not the active forwarding path. This step is non-negotiable.

text

show chassis routing-engine | match "Slot|Current state|Mastership"
show route summary | match "Router ID"
show system uptime

Verify: your session is on the master RE. If Current state shows Backup, switch to master: request routing-engine login other-routing-engine.

On single-RE platforms, confirm RE is Master (not in a degraded state). Record: hostname, RE slot, mastership state, uptime, last reboot reason. Short uptime after an unexpected reboot — investigate immediately.

Step 2: Alarm Analysis#

JunOS surfaces alarms as first-class status indicators. Check chassis and system alarms before deeper investigation — alarms may already identify the problem.

text

show chassis alarms
show system alarms

Alarm severities:

• Major — service-affecting condition, requires immediate attention
• Minor — degraded but service continues, investigate promptly

If alarms are present, record each alarm's class, description, and time. Major alarms take priority over all other triage — address them first. Common alarm sources: FPC offline, power supply failure, rescue config not set, license expiry, FRU removal.

No alarms → proceed with systematic health assessment.

Step 3: Routing Engine Health#

RE handles control plane: routing protocols, management, commit operations.

text

show chassis routing-engine
show system processes extensive | match "PID|last pid|%CPU" | head 20
show task replication

Key fields from show chassis routing-engine:

• CPU utilization — temperature, idle percentage (idle below 30% is warning)
• Memory utilization — total and used; watch for used > 80%
• Temperature — compare to platform-specific thresholds
• Start time — recent RE restart indicates crash or failover
• Load averages — 1min/5min/15min; sustained > 1.0 per core is elevated

High RE CPU with top process identification:

• rpd — routing protocol daemon: route churn, table size, peer instability
• chassisd — chassis management: sensor polling issues, FPC communication
• snmpd — SNMP polling storms
• mgd — management: large config, slow commit, CLI session overload
• kmd — key management: IKE/IPsec negotiation storms (SRX)

RE CPU spikes during commit operations are normal (can hit 80–90% briefly). Compare against commit history: show system commit.

Step 4: PFE Health#

PFE handles data plane forwarding independently from RE. A healthy RE with a degraded PFE means traffic is being dropped even though the control plane looks fine.

text

show chassis fpc
show chassis fpc detail
show pfe statistics traffic
show pfe statistics error

show chassis fpc:

• State must be Online. Any other state ( Present, Offline, Empty) indicates a hardware issue or intentional deactivation.
• CPU Total — PFE CPU utilization; above 80% is warning, above 90% critical
• Memory heap utilization — above 80% indicates PFE memory pressure

show pfe statistics traffic:

• Compare input vs output packet counts — large delta indicates drops
• Check fabric input drops and local input drops for discard sources

show pfe statistics error:

• Any non-zero error counters warrant investigation
• Sustained incrementing errors (check twice 30 seconds apart) indicate active issues

On MX platforms with multiple FPCs, check each FPC individually. A single degraded FPC affects only interfaces on that linecard.

Step 5: System Resources#

text

show system storage
show system memory
show system core-dumps
show system commit | head 10

Storage: JunOS partitions can fill from logs, core dumps, or failed upgrades. Any partition above 85% used is warning. /var filling above 90% can prevent commits and logging.

Memory: show system memory gives kernel-level view. Compare to RE memory from Step 3 for consistency. Sustained growth without corresponding config changes suggests a memory leak.

Core dumps: Presence of recent core files (within last 7 days) indicates process crashes. Record the process name and timestamp — this is JTAC-relevant data.

Commit history: Recent commits correlate with symptoms. A device that was healthy before a commit and unhealthy after has an obvious investigation path.

Step 6: Interface and Routing Health#

text

show interfaces terse | match "down|err"
show interfaces extensive [name] | match "error|drop|CRC|carrier"
show route summary
show bgp summary
show ospf neighbor
show isis adjacency

For each interface with errors:

• CRC errors → Layer 1 (cabling, optics, SFP)
• Input errors without CRC → buffer overruns, MTU mismatch
• Output drops → congestion or policer drops
• Carrier transitions → link flap, check SFP DOM: show interfaces diagnostics optics [name]

Routing: verify expected neighbor count, all adjacencies in Established/Full state. BGP prefix counts deviating > 10% from baseline indicate route churn.

Step 7: Environment#

text

show chassis environment
show chassis temperature-thresholds
show chassis power
show chassis fan

Check: all temperature sensors within thresholds, all power supplies OK, all fans operational. Any environmental alarm maps directly to Major alarm severity.

On platforms with redundant RE: check both RE temperatures. A standby RE running hot may indicate cooling issues even if master RE temperature is normal.

Threshold Tables#

Reference: references/threshold-tables.md for detailed per-parameter thresholds.

ParameterNormalWarningCriticalNotesRE CPU idle> 40%20–40%< 20%Spikes during commit are normalRE memory used< 75%75–85%> 85%RE load avg (1min)< 0.7/core0.7–1.5/core> 1.5/coreScale by RE core countPFE CPU< 60%60–80%> 80%Per-FPCPFE heap used< 70%70–85%> 85%Per-FPCStorage partition< 80%80–90%> 90%/var critical for commitsInterface error rate< 0.01%0.01–0.1%> 0.1%Output drops/hr< 100100–1000> 1000Chassis alarmNoneMinor presentMajor presentTemperatureWithin spec5°C of maxAt/above maxPer-sensor

Decision Trees#

Primary Triage#

text

Is the device reachable?
├── No → Check console, power, environment. Collect core dumps after recovery.
└── Yes
    ├── Verify RE mastership → On master RE?
    │   ├── No → Switch to master RE, restart triage
    │   └── Yes → Continue
    │
    ├── Chassis/system alarms present?
    │   ├── Major alarm → Address immediately
    │   │   ├── FPC offline → show chassis fpc detail, check PFE
    │   │   ├── Power supply failure → show chassis power, environment
    │   │   ├── RE failover → show chassis routing-engine, check standby
    │   │   └── Other Major → Collect alarm detail, escalate
    │   ├── Minor alarm → Note for report, continue triage
    │   └── No alarms → Continue systematic assessment
    │
    ├── RE CPU issue?
    │   ├── rpd high → Route churn: check BGP/OSPF/ISIS neighbors
    │   ├── chassisd high → FPC/sensor communication: check chassis fpc
    │   ├── snmpd high → Polling storm: check SNMP community/clients
    │   ├── mgd high → Commit or CLI overload: check system commit
    │   ├── kmd high → IKE storms (SRX): check IPsec SA count
    │   └── Recent commit correlates → Rollback candidate
    │
    ├── PFE issue? (RE healthy but traffic drops)
    │   ├── FPC not Online → Hardware issue, check fpc detail
    │   ├── PFE CPU > 80% → Forwarding overload
    │   │   └── Check traffic rates, filter complexity, NH resolution
    │   ├── PFE drops incrementing → Identify drop category
    │   │   ├── Fabric drops → Linecard-to-fabric issue
    │   │   ├── Local drops → Punt/exception path overload
    │   │   └── Discard → Filter or policer drops (may be expected)
    │   └── PFE memory pressure → Session/route table exhaustion
    │
    ├── Memory issue?
    │   ├── RE memory > 85% → Identify top consumers via processes
    │   ├── Storage > 90% → Clean logs, core dumps, old images
    │   │   └── /var full → Immediate: prevents commits and logging
    │   └── Core dumps present → Process crash, collect for JTAC
    │
    ├── Interface errors? → Classify error type
    │   ├── CRC/input errors → Layer 1 (cable, optic, SFP)
    │   ├── Output drops → QoS policer or congestion
    │   └── Carrier transitions → Link flap, check optics DOM
    │
    └── All within thresholds → Document clean health

Alarm Severity Triage#

text

Alarm detected
├── Major alarm?
│   ├── FPC Offline
│   │   ├── Single FPC → Affects only interfaces on that linecard
│   │   ├── check: show chassis fpc detail [slot]
│   │   └── Action: power cycle FPC if transient, RMA if persistent
│   ├── Power Supply Failure
│   │   ├── Redundancy lost → Immediate replacement
│   │   └── Both PSUs failed → Emergency, device at risk
│   ├── RE Failover
│   │   ├── Was this planned? → Verify new master is healthy
│   │   └── Unplanned → Investigate old master: show chassis routing-engine
│   └── Other Major → Collect detail, open JTAC case
│
└── Minor alarm?
    ├── Rescue config not set → `request system configuration rescue save`
    ├── License expiry → Check feature impact, plan renewal
    ├── FRU removal → Verify intentional, document
    └── Other Minor → Note in report, monitor

Escalation Criteria#

Escalate to senior engineer or JTAC when:

• RE CPU sustained above 90% for 15+ minutes with no identifiable cause
• RE memory above 90% used with no recent config change
• PFE offline or in non-Online state after power cycle attempt
• Core dumps present from critical processes (rpd, chassisd, pfed)
• Major chassis alarm with no clear remediation
• Multiple FPC failures or fabric errors
• RE failover loop (multiple failovers in short period)
• Any environmental alarm (power, fan, temperature)
• More than 3 routing neighbor state changes in the last hour

Report Template#

text

DEVICE HEALTH REPORT
====================
Device: [hostname]
Platform: JunOS
Model: [from show chassis hardware]
Software: [JunOS version]
RE Slot: [RE0 or RE1]
Mastership: [Master — verified]
Uptime: [uptime string]
Check Time: [timestamp]
Performed By: [operator/agent]

SUMMARY: [HEALTHY | WARNING | CRITICAL | EMERGENCY]

ALARMS:
  Chassis: [count] ([Major: n, Minor: n] or None)
  System: [count] ([Major: n, Minor: n] or None)
  Details: [alarm descriptions if present]

FINDINGS:
1. [Severity] [Component] — [Description]
   Domain: [RE | PFE | Chassis | Interface | Routing]
   Observed: [metric value]
   Threshold: [normal/warning/critical range]
   Action: [recommended action]

2. ...

RE/PFE STATUS:
  RE: [healthy/degraded/critical] — CPU idle: [n]%, Memory: [n]% used
  PFE: [per-FPC state summary]
  Dual-RE: [master/backup state, or N/A for single-RE]

RECOMMENDATIONS:
- [Prioritized action list]

NEXT CHECK: [date based on severity — CRITICAL: 24hr, WARNING: 7d, HEALTHY: 30d]

Troubleshooting#

Device Unresponsive to SSH#

Try console access. If console is also unresponsive, check power and environment via out-of-band management (craft interface, console server). After recovery: show system core-dumps, show chassis routing-engine for reboot reason, show log messages | match "kernel|panic|watchdog".

Logged Into Backup RE#

If show chassis routing-engine shows your RE as Backup, you are collecting standby metrics. Switch to master: request routing-engine login other-routing-engine. If master RE is unreachable from backup, this indicates master RE failure — check show chassis routing-engine from backup for master's last known state.

RE CPU Spikes During Commit#

JunOS RE CPU can spike to 80–90% during commit operations. This is expected behavior — the config daemon and rpd both consume CPU during commit processing. Verify: show system commit to confirm a recent commit, then wait 2–3 minutes and re-check. Sustained high CPU after commit settles indicates a real problem.

PFE Drops With Healthy RE#

The RE (control plane) and PFE (data plane) are independent. High PFE drops with a normal RE means traffic is being discarded at the forwarding level. Check: show pfe statistics traffic for drop categories, show chassis fpc detail for PFE CPU and memory. Common causes: filter/policer drops (may be expected), next-hop resolution failures, PFE memory exhaustion from large tables.

Storage Full Preventing Commits#

If /var is above 95%, commits will fail. Clear space: request system storage cleanup — removes old logs, core dumps, and temporary files. If that is insufficient: show system storage to identify the largest consumers, then selectively remove old software images or rotated log files.

Dual-RE Failover Investigation#

After an RE failover: verify new master is healthy (Steps 1–3), then investigate the old master. From the new master: show chassis routing-engine shows both REs' state. Check show log messages | match "mastership|failover|switchover" for the event trigger. Common causes: RE crash (core dump present), watchdog timeout, manual switchover, GRES/NSR failure.