SNMP vs. Syslog: Understanding Traps, Polling, and When to Use Each

What Is SNMP?

SNMP (Simple Network Management Protocol) is built for structured monitoring and device management. It works in two primary modes:

1) SNMP Polling

• How it works: Your NMS (Network Management System) periodically requests metrics (OIDs) from devices.
• Use it for: Interface utilization, CPU/memory, errors, discards—anything you want to graph and trend.
• Pros: Predictable and reliable; perfect for baselines, capacity planning, and SLA reporting.
• Cons: Can generate overhead at scale if polling many OIDs frequently.

2) SNMP Traps (and Informs)

• How it works: Devices send unsolicited notifications to your NMS when events occur (e.g., link down, PSU failure).
• Pros: Real-time alerts—no waiting for the next polling cycle.
• Cons: Traps use UDP and can be dropped; informs add acknowledgments for reliability.

Check out my post on Polling vs Traps:

SNMP Polling vs Traps

What Is Syslog?

Syslog forwards text-based log messages to a centralized collector. Messages carry a severity from 0 (Emergency) to 7 (Debug) and include details about software events, config changes, security notices, and more.

• Flexible: Free-form messages capture rich context that SNMP doesn’t.
• Great for: Troubleshooting timelines, security/audit trails, error analysis, and correlation.

When to Use Each

Real-World Flow

Interface failure example:

• SNMP Trap: Device immediately alerts the NMS that Gi0/1 is down.
• SNMP Polling: At the next poll, utilization drops; graphs show the time of impact.
• Syslog: Records %LINK-3-UPDOWN with timestamps and additional context for troubleshooting.

Design Tips & Best Practices

• Use informs for critical notifications where delivery matters.
• Throttle/aggregate traps and syslog to avoid floods during big events.
• Encrypt in transit: Prefer SNMPv3 for auth/privacy and Syslog over TCP/TLS when supported.
• Standardize severity (Syslog) and MIBs/OIDs (SNMP) across vendors where possible.
• Correlate SNMP and Syslog in your monitoring stack for faster MTTR.

Cisco Configuration Examples

SNMP (Polling & Traps)

! Community for v2c (use v3 in production)
snmp-server community public RO

! SNMPv3 example (preferred)
snmp-server group NMS v3 priv
snmp-server user nmsuser NMS v3 auth sha StrongAuthPass priv aes 128 StrongPrivPass

! Send traps to NMS
snmp-server host 192.0.2.10 version 3 priv nmsuser
! or for v2c:
! snmp-server host 192.0.2.10 version 2c public

! Enable trap types (pick what you need)
snmp-server enable traps snmp
snmp-server enable traps config
snmp-server enable traps syslog
snmp-server enable traps link
snmp-server enable traps envmon

Verify with “show snmp host”, “show run | inc snmp”, “show snmp group”, “show snmp statistics”, etc….

Syslog

! Turn on logging and point to your collector
logging on
logging host 198.51.100.20
! Optionally use TCP/TLS if supported on your platform:
! logging host 198.51.100.20 transport tcp port 6514

! Control what gets sent (0=emergencies ... 7=debug)
logging trap informational

! Useful quality-of-life settings
logging buffered 16384 informational
service timestamps log datetime msec
logging source-interface Loopback0

See configuration and local buffer with “show logging”.

Key Takeaways

• SNMP Polling = scheduled health checks and trends.
• SNMP Traps/Informs = instant, event-driven alerts.
• Syslog = detailed, text-based event history for investigation and audits.
• Together they deliver the full picture: visibility, alerting, and context.