Arista EOS Device Health Check

Structured triage procedure for assessing Arista EOS device health. Produces a prioritized findings report with severity classifications and recommended actions.

EOS runs on a Linux kernel with individual processes (agents) managing each protocol and subsystem. This architecture means Linux-native tools (bash top, bash df, bash dmesg) are valid supplements to EOS show commands. Agent health is a first-class concern — a crashed or stuck agent can silently affect a subsystem even when aggregate device metrics look normal.

The procedure covers core device health first, then extends to MLAG and VXLAN/EVPN for data center deployments.

When to Use

• Device reported as slow, dropping traffic, or unresponsive
• Scheduled health audit of Arista switches (leaf, spine, or border)
• Post-change verification after upgrades, patches, or configuration changes
• Capacity planning data collection for CPU, memory, and link utilization
• Incident response when an Arista switch is suspected as the fault domain
• MLAG inconsistency or split-brain detection in a data center pair
• VXLAN/EVPN overlay health assessment — VTEP reachability, BGP EVPN peering
• Agent crash or restart detected in syslog

Prerequisites

• SSH or console access to the device (privilege 1 minimum)
• EOS 4.28 or later (commands validated against EOS 4.30+)
• Network reachability to management interface confirmed
• Awareness of the device's normal baseline (CPU, memory, traffic patterns)
• For MLAG configurations: access to both MLAG peers for cross-validation
• For VXLAN/EVPN: knowledge of expected VTEP count and BGP EVPN peer list

Procedure

Follow this sequence. Core device health (Steps 1–5) applies to all deployments. Steps 6–7 are data center extensions for MLAG and VXLAN/EVPN — skip if not configured on this device.

Step 1: Establish Baseline Context

show version
show uptime
show clock
show inventory

Record: hostname, EOS version, uptime, hardware model, total memory, current time. Short uptime indicates a recent reload or crash — check show reload cause for the trigger. Note the hardware platform — Arista's 7050X, 7280R, 7500R, and 720X series have different memory and CPU profiles.

Step 2: CPU and Memory Assessment

EOS reports CPU and memory through both EOS commands and Linux-native tools.

show processes top once
show version | include Free memory

Linux-native alternative (provides more granularity):

bash timeout 5 top -bn1 | head 20
bash free -m

show processes top once shows per-process CPU and memory similar to Linux top. EOS CPU is typically consumed by agents — each protocol has its own process.

Key agents to watch:

• Stp — Spanning Tree: high CPU indicates topology instability
• Rib — Routing Information Base: route churn or large table operations
• Ebra — EOS Bridge Agent: L2 forwarding, MAC learning storms
• IpRib — IP RIB agent: routing table processing
• Bgp — BGP agent: peer negotiations, route processing
• Fap-sobek / Sand — ASIC agents: forwarding plane, hardware programming

EOS memory: show version includes total and free memory. Free memory below 20% of total is warning. Linux free -m provides buffer/cache detail — EOS uses Linux page cache aggressively, so "used" memory includes reclaimable cache.

Step 3: Agent and Daemon Health

EOS runs each subsystem as an independent agent. A crashed or stuck agent affects its subsystem silently — device-level metrics may look normal while one protocol is completely inoperative.

show agent
show agent [name] logs | tail 20
show logging last 50 | include AGENT|agent|crash|restart

show agent lists all EOS agents with their PID, state, and uptime.

Healthy state: all agents show running with uptimes matching device uptime. Red flags:

• Agent with shorter uptime than device → it crashed and restarted
• Agent in crashed or not running state → subsystem is down
• Multiple agent restarts in logs → recurring instability

If an agent shows recent restart, check its logs: show agent [name] logs. Common restart causes: memory exhaustion, uncaught exception, watchdog timeout.

Step 4: Interface Health

show interfaces status
show interfaces counters errors
show interfaces counters discards

For interfaces with errors:

show interfaces [name]
show interfaces [name] transceiver

Error classification:

• CRC / FCS errors → Layer 1 (cabling, optics, SFP seating)
• Input errors without CRC → buffer overruns, MTU mismatch
• Alignment errors → duplex mismatch or L1 issue
• Output discards → egress congestion; check QoS or link capacity
• Late collisions → duplex mismatch (should not occur on modern links)

Optics DOM: show interfaces transceiver provides Tx/Rx power, temperature, voltage. Low Rx power (below -10 dBm for most 10G SFP+) indicates fiber or optic degradation.

Step 5: Environment and Platform

show environment all
show environment cooling
show environment power
show environment temperature
show reload cause
show logging last 30 | include ERR|WARN|traceback|panic

Check: all temperature sensors within limits, all power supplies OK, all fans operational. show environment all is a comprehensive single command.

show reload cause — if the device recently reloaded, this explains why. Expected causes: user-initiated, software upgrade. Unexpected causes: kernel panic, watchdog timeout, power loss.

Review syslog for tracebacks, panics, or agent crashes. EOS logs are also accessible via bash cat /var/log/messages | tail 50.

Step 6: MLAG Health (Data Center Extension)

Skip this step if MLAG is not configured. MLAG state is often the single most important health indicator in an Arista data center deployment — a degraded MLAG pair can cause traffic black-holes or asymmetric forwarding.

show mlag
show mlag detail
show mlag interfaces
show mlag config-sanity

MLAG state assessment:

show mlag detail provides:

• Peer address and peer-link interface status
• Heartbeat interval and status — lost heartbeats indicate control plane reachability issues between peers
• Reload delay timers — critical for preventing traffic loss during boot

show mlag config-sanity checks for configuration mismatches between peers. Inconsistencies can cause traffic loops or black-holes. Address any inconsistent result before continuing other triage.

show mlag interfaces — verify all MLAG interfaces show active-full on both sides. active-partial means one side is down — reduced redundancy. disabled means the MLAG interface is administratively or operationally down.

Step 7: VXLAN/EVPN Health (Data Center Extension)

Skip this step if VXLAN/EVPN is not configured. This assesses overlay fabric health for VXLAN deployments using BGP EVPN as the control plane.

show vxlan vtep
show vxlan address-table
show interfaces vxlan 1
show bgp evpn summary

VXLAN health checks:

• show vxlan vtep — verify expected VTEP count. Missing VTEPs indicate underlay reachability or BGP EVPN peering issues.
• show interfaces vxlan 1 — VTEP source interface must be up. Flood list should match expected remote VTEPs (for flood-and-learn) or be empty (for BGP EVPN with ingress replication).
• show vxlan address-table — MAC learning across the overlay. Stale or missing entries indicate control plane issues.

BGP EVPN peering:

• show bgp evpn summary — all EVPN peers must be in Established state. Peers in Active/Connect state have transport or configuration issues.
• Compare EVPN route count to baseline — significant deviation indicates route withdrawal or redistribution problems.

For L3 VXLAN (symmetric IRB):

show ip route vrf [name] summary
show bgp evpn route-type ip-prefix

Verify: VRF route counts match expectations, no unexpected route withdrawals, EVPN type-5 routes present for inter-VRF routing.

Threshold Tables

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

Decision Trees

Primary Triage

Is the device reachable?
├── No → Check console, power, environment. Check reload cause after recovery.
└── Yes
    ├── Agent health issue?
    │   ├── Agent crashed / not running → Subsystem is down
    │   │   ├── Identify which agent → Determines affected protocol/feature
    │   │   ├── Bgp agent → BGP sessions will be down
    │   │   ├── Stp agent → STP not running, L2 loops possible
    │   │   ├── Ebra agent → L2 forwarding affected
    │   │   └── Action: check agent logs, attempt restart, escalate to TAC
    │   ├── Agent restarted recently → Subsystem had a disruption
    │   │   └── Check logs: `show agent [name] logs` for crash reason
    │   └── All agents running, uptimes match → Agent layer healthy
    │
    ├── CPU issue?
    │   ├── Identify top agent by CPU
    │   │   ├── Stp high → STP topology change, check link flaps
    │   │   ├── Rib/IpRib high → Route churn, check BGP/OSPF peers
    │   │   ├── Ebra high → MAC learning storm, check for loops
    │   │   ├── Bgp high → Large table, peer negotiation, route policy
    │   │   └── Fap/Sand high → ASIC programming backlog
    │   └── No single agent dominant → General overload, check traffic rates
    │
    ├── Memory issue?
    │   ├── Free \x3C 20% → Check top consumers via `show processes top once`
    │   ├── Linux cache: `bash free -m` → Cache is reclaimable, not a real leak
    │   └── Steady growth → Memory leak in agent, collect data, plan reload
    │
    ├── Interface errors? → Classify error type
    │   ├── CRC/FCS errors → Layer 1 (cable, optic, SFP)
    │   ├── Output discards → QoS or congestion
    │   └── Alignment errors → Duplex mismatch
    │
    ├── MLAG issue? (if configured)
    │   ├── See MLAG State Triage tree below
    │   └── MLAG healthy → Continue
    │
    ├── VXLAN/EVPN issue? (if configured)
    │   ├── Missing VTEPs → Check underlay reachability, BGP EVPN peers
    │   ├── EVPN peer not Established → Check transport, route-map, ASN
    │   └── VTEP and peers OK → Overlay healthy
    │
    └── All within thresholds → Document clean health

MLAG State Triage

MLAG configured?
├── No → Skip MLAG checks
└── Yes
    ├── MLAG state: active?
    │   ├── No → MLAG disabled or inactive
    │   │   └── Check: `show mlag` for reason, peer reachability
    │   └── Yes → Continue
    │
    ├── Peer-link status: up?
    │   ├── No → CRITICAL — peer-link down
    │   │   ├── Traffic orphaned on MLAG interfaces
    │   │   ├── Check: physical link, SFP, port-channel members
    │   │   └── Verify: reload-delay timers configured to prevent storms
    │   └── Yes → Continue
    │
    ├── Negotiation: connected?
    │   ├── No → Control plane issue between peers
    │   │   └── Check: heartbeat, peer IP, VLAN configuration
    │   └── Yes → Continue
    │
    ├── Config sanity: consistent?
    │   ├── No → Configuration mismatch
    │   │   ├── `show mlag config-sanity` for details
    │   │   ├── Common: VLAN mismatch, STP priority, trunk allowed VLANs
    │   │   └── Fix mismatches before trusting MLAG state
    │   └── Yes → Continue
    │
    ├── MLAG interfaces: all active-full?
    │   ├── active-partial → One side down, reduced redundancy
    │   │   └── Check: interface status on both peers
    │   ├── disabled → Interface operationally down
    │   │   └── Check: physical link, member port status
    │   └── active-full → Healthy
    │
    └── All checks pass → MLAG healthy

Escalation Criteria

Escalate to senior engineer or Arista TAC when:

• CPU sustained > 90% for 15+ minutes with no identifiable cause
• Memory below 15% free with no recent change to explain consumption
• Agent in crashed state that does not recover after restart
• Multiple agents crashing or restarting within a short period
• Traceback or kernel panic in logs (show logging, bash dmesg)
• Any environmental alarm (power, fan, temperature)
• More than 3 routing neighbor state changes in the last hour
• MLAG peer-link failure with no clear physical cause
• MLAG config-sanity inconsistencies that cannot be resolved
• VXLAN overlay losing more than 10% of expected VTEPs

Report Template

DEVICE HEALTH REPORT
====================
Device: [hostname]
Platform: Arista EOS
Model: [from show inventory]
Software: [EOS version]
Uptime: [uptime string]
Check Time: [timestamp]
Performed By: [operator/agent]

SUMMARY: [HEALTHY | WARNING | CRITICAL | EMERGENCY]

AGENT HEALTH:
  Total agents: [count]
  Running: [count] | Crashed: [count] | Not running: [count]
  Recent restarts: [list any agents with uptime \x3C device uptime]

FINDINGS:
1. [Severity] [Component] — [Description]
   Domain: [System | Interface | MLAG | VXLAN | Environment]
   Observed: [metric value]
   Threshold: [normal/warning/critical range]
   Action: [recommended action]

2. ...

DC EXTENSIONS:
  MLAG: [healthy | degraded | critical | not configured]
    State: [active/inactive], Peer-link: [up/down], Config-sanity: [consistent/inconsistent]
  VXLAN/EVPN: [healthy | degraded | critical | not configured]
    VTEPs: [observed/expected], EVPN peers: [established/total]

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. After recovery: show reload cause for the trigger, bash dmesg | tail 50 for kernel messages, show logging last 50 for pre-crash syslog. EOS stores crash data in /var/log/ — accessible via bash ls -la /var/log/.

Agent Crash and Recovery

If show agent shows an agent as crashed or with uptime shorter than the device:

1. Check agent logs: show agent [name] logs | tail 30
2. Check syslog: show logging last 50 | include [agent-name]
3. Linux-level: bash journalctl -u [agent-name] --no-pager | tail 30
4. If the agent is not running, attempt: agent [name] shutdown then no agent [name] shutdown in configuration mode (note: this is a config change)

Agent crashes are the most common EOS-specific failure mode. Collect logs before restarting — the crash data is needed for TAC investigation.

CPU Spikes During Health Check

EOS show commands can briefly spike CPU on the management plane. Wait 30 seconds after connecting before collecting CPU data. Use show processes top once rather than interactive top (which holds a session) for scripted checks.

MLAG Split-Brain Detection

If both peers report MLAG state active but negotiation shows disconnected, this is a split-brain condition. Both peers believe they are the primary. Causes: peer-link physical failure, peer-link VLAN issue, or heartbeat network partition. Immediate action: verify physical peer-link connectivity. If peer-link is physically up but MLAG reports disconnected, check VLAN trunking on the peer-link and the heartbeat network (usually the management VRF).

Linux-Native Diagnostics

EOS's Linux foundation means standard Linux tools work from bash:

• bash top -bn1 — process-level CPU and memory (more granular than EOS top)
• bash free -m — memory with buffer/cache detail
• bash df -h — filesystem usage (important for /mnt/flash and /var/log)
• bash dmesg | tail — kernel messages (hardware errors, driver issues)
• bash uptime — load averages
• bash cat /proc/meminfo — detailed memory breakdown

These supplement EOS show commands when deeper investigation is needed. Prefix all commands with bash from the EOS CLI, or enter bash for a shell.

Inconsistent Memory Readings

EOS's Linux page cache uses available memory for file caching. show version may report low free memory while actual memory pressure is low. Use bash free -m and check the available column (not free) for the real available memory. The available column accounts for reclaimable cache and buffers.