SNMP Monitoring

Chapter 41: SNMP and Network Monitoring

Overview

This chapter covers SNMP (Simple Network Management Protocol) for network monitoring.

41.1 SNMP Basics

SNMP Versions

              SNMP Versions
+------------------------------------------------------------------+
|                                                                   |
|   SNMPv1   - Original, security by community string              |
|   +------------------------------------------------------------+ |
|   | Read-only and read-write communities                       | |
|   +------------------------------------------------------------+ |
|                                                                   |
|   SNMPv2c  - Like v1 with enhanced operations                   |
|   +------------------------------------------------------------+ |
|   | GetBulk, GetNext improvements                              | |
|   +------------------------------------------------------------+ |
|                                                                   |
|   SNMPv3   - Secure version                                     |
|   +------------------------------------------------------------+ |
|   | User-based (USM), View-based (VACM)                        | |
|   | Authentication: MD5, SHA                                  | |
|   | Encryption: DES, AES                                      | |
|   +------------------------------------------------------------+ |
|                                                                   |
+------------------------------------------------------------------+

41.2 SNMP OIDs

Common OIDs

# System
1.3.6.1.2.1.1.1.0   - sysDescr
1.3.6.1.2.1.1.3.0   - sysUpTime
1.3.6.1.2.1.1.5.0   - sysName

# Interface
1.3.6.1.2.2.1.1.2   - ifNumber
1.3.6.1.2.2.1.2.2   - ifDescr
1.3.6.1.2.2.1.10.2  - ifInOctets
1.3.6.1.2.2.1.16.2  - ifOutOctets

# CPU
1.3.6.1.4.1.2021.10.1.5.1 - laLoad.1 (5-min)
1.3.6.1.4.1.2021.10.1.6.1 - laLoad.2 (10-min)

# Memory
1.3.6.1.4.1.2021.4.5.0   - memTotalReal
1.3.6.1.4.1.2021.4.6.0   - memAvailReal
1.3.6.1.4.1.2021.4.11.0  - memTotalFree

41.3 SNMP Tools

snmpwalk

# Walk all OIDs
snmpwalk -v2c -c public localhost

# Walk system OIDs
snmpwalk -v2c -c public localhost system

# Walk interface info
snmpwalk -v2c -c public localhost interfaces

# Get specific OID
snmpget -v2c -c public localhost sysUpTime.0

# Get multiple OIDs
snmpget -v2c -c public localhost sysUpTime.0 sysContact.0

snmpget

# Get system description
snmpget -v2c -c public localhost sysDescr.0

# Get interface statistics
snmpget -v2c -c public localhost ifInOctets.1 ifOutOctets.1

# Get CPU load
snmpget -v2c -c public localhost laLoad.1

41.4 SNMP Configuration

snmpd Configuration

# /etc/snmp/snmpd.conf (snmpd.conf)

# SNMPv2c community
rocommunity public
rwcommunity private

# SNMPv3 user
createUser admin MD5 "mypassword" DES
rouser admin authPriv

# System location
syslocation "Data Center Rack 1"
syscontact admin@example.com

# Agent configuration
agentAddress udp:161

Client Configuration

# Default community
defCommunity public

# Default version
defVersion 2c

41.5 Network Monitoring Tools

nagios-plugins

# Check CPU
check_cpu -w 80 -c 90

# Check memory
check_memory -w 80 -c 90

# Check disk
check_disk -w 20% -c 10% -p /

# Check load
check_load -w 1.5,1.2,1.0 -c 2.0,1.8,1.5

Monitoring Tools Comparison

# Nagios/Icinga      - Traditional monitoring
# Zabbix             - Enterprise monitoring
# Prometheus         - Metrics-based
# Grafana            - Visualization
# Cacti              - Graphing (RRDTool)
# Smokeping          - Latency monitoring

Why This Matters in DevOps/SRE

SNMP remains important for network infrastructure monitoring:

              SNMP in Enterprise Monitoring
+------------------------------------------------------------------+
|                                                                   |
|    Network Devices:                                                 |
|    +----------------------------------------------------------+  |
|    | Routers → Interface statistics                         |  |
|    | Switches → Port usage, VLANs                          |  |
|    | Firewalls → Connection tables                         |  |
|    | UPS → Battery status, load                           |  |
|    +----------------------------------------------------------+  |
|                                                                   |
|    Hardware Monitoring:                                             |
|    +----------------------------------------------------------+  |
|    | iLO → HP server hardware                              |  |
|    | iDRAC → Dell server hardware                          |  |
|    | IPMI → Baseboard management                           |  |
|    +----------------------------------------------------------+  |
|                                                                   |
|    Modern Integration:                                              |
|    +----------------------------------------------------------+  |
|    | SNMP exporter → Prometheus metrics                    |  |
|    | Zabbix → Enterprise SNMP monitoring                  |  |
|    | LibreNMS → Open source SNMP                          |  |
|    +----------------------------------------------------------+  |
|                                                                   |
+------------------------------------------------------------------+

Practical Impact:

Monitor network infrastructure at scale
Hardware health monitoring for servers
Integration with modern monitoring systems

Common Mistakes & Anti-Patterns

1. Using SNMPv1/v2c in Production

# ❌ WRONG: Using unencrypted SNMPv2c
snmpget -v 2c -c public target OID
# Community string sent in plain text!

# ✅ CORRECT: Use SNMPv3 with auth
snmpget -v 3 -u myuser -l authPriv -a SHA -A myauthpass -x AES -X myprivpass target OID

2. Not Using Correct OID Format

# ❌ WRONG: Using numeric OID only
snmpget target 1.3.6.1.2.1.1.1.0
# Hard to read and maintain

# ✅ CORRECT: Use symbolic names
snmpget target sysDescr.0
snmpget target sysUpTime.0

3. Polling Too Frequently

# ❌ WRONG: Polling every second
* * * * * snmpwalk target  # Every minute is too much

# ✅ CORRECT: Appropriate polling interval
# Network stats: 1-5 minutes
# Interface counters: 5-10 minutes
# Hardware sensors: 5-15 minutes

Interview Questions

What are the different SNMP versions?
What is the difference between SNMP GET, GETNEXT, and WALK?
Explain OID and MIB.
What is SNMPv3 security?
How do you monitor network devices with SNMP?

Summary

In this chapter, you learned:

✅ SNMP versions and security
✅ Common OIDs
✅ SNMP tools (snmpwalk, snmpget)
✅ SNMP configuration
✅ Network monitoring tools

Part 8 Summary

In this part, you learned:

✅ System logging (rsyslog, syslog-ng)
✅ Logrotate for log management
✅ System monitoring tools
✅ Prometheus and Grafana
✅ SNMP monitoring

Next Chapter

Chapter 42: Backup Strategies and Concepts

Last Updated: February 2026