Implement SNMP trap monitoring and alerting system for proactive network management

Intermediate 45 min Apr 15, 2026 846 views
Ubuntu 24.04 Debian 12 AlmaLinux 9 Rocky Linux 9

Set up comprehensive SNMP trap monitoring with snmptrapd, automated alerting via email and webhooks, and integration with monitoring platforms like Nagios and Zabbix for proactive network management and real-time issue detection.

Prerequisites

  • Root access
  • Basic SNMP knowledge
  • Network devices that support SNMP traps
  • Email server (postfix) for notifications

What this solves

SNMP trap monitoring provides proactive network management by receiving and processing unsolicited notifications from network devices when events occur. This tutorial sets up a complete trap monitoring system with Net-SNMP 5.9, automated alerting through multiple channels, and integration with existing monitoring platforms for comprehensive network visibility.

Step-by-step installation

Update system packages

Start by updating your package manager to ensure you get the latest versions of SNMP packages.

sudo apt update && sudo apt upgrade -y
sudo dnf update -y

Install SNMP packages and MIB tools

Install Net-SNMP daemon, utilities, and MIB management tools for comprehensive trap handling.

sudo apt install -y snmp snmp-mibs-downloader snmptrapd postfix mailutils curl jq
sudo dnf install -y net-snmp net-snmp-utils postfix mailx curl jq

Create trap handler directory structure

Set up directories for trap handlers, logs, and configuration files with proper permissions.

sudo mkdir -p /etc/snmp/traphandlers
sudo mkdir -p /var/log/snmp/traps
sudo mkdir -p /var/lib/snmp/trapdb
sudo chown -R snmp:snmp /var/log/snmp
sudo chown -R snmp:snmp /var/lib/snmp
sudo chmod 755 /etc/snmp/traphandlers

Configure snmptrapd daemon

Create the main snmptrapd configuration file with trap receiving settings and handler definitions.

# SNMP Trap Daemon Configuration
# Listen on all interfaces, port 162 (standard SNMP trap port)
snmpTrapdAddr udp:162,udp6:162

# Authentication settings
disableAuthorization yes

# Logging configuration
logOption s 6
logTimestamp yes

# Output format for traps
format1 %.4y-%.2m-%.2l %.2h:%.2j:%.2k [%B] %N: %W\n\t%V\n
format2 %.4y-%.2m-%.2l %.2h:%.2j:%.2k [%B] %N: Enterprise Specific Trap (%w) Uptime: %#T\n\t%v\n

# Trap handlers for different trap types
traphandle default /etc/snmp/traphandlers/default_handler.sh
traphandle SNMPv2-MIB::coldStart /etc/snmp/traphandlers/system_handler.sh
traphandle SNMPv2-MIB::warmStart /etc/snmp/traphandlers/system_handler.sh
traphandle SNMPv2-MIB::linkDown /etc/snmp/traphandlers/interface_handler.sh
traphandle SNMPv2-MIB::linkUp /etc/snmp/traphandlers/interface_handler.sh
traphandle SNMPv2-MIB::authenticationFailure /etc/snmp/traphandlers/security_handler.sh

# Create PID file
pidFile /var/run/snmptrapd.pid

# Run as snmp user
agentuser snmp

Create default trap handler script

Build the main trap processing script that logs all traps and triggers alert mechanisms.

#!/bin/bash

# Default SNMP Trap Handler
# Processes all incoming SNMP traps and triggers alerts

TRAP_LOG="/var/log/snmp/traps/default.log"
ALERT_CONFIG="/etc/snmp/alert_config.conf"
TRAP_DB="/var/lib/snmp/trapdb/traps.db"

# Source alerting configuration
if [ -f "$ALERT_CONFIG" ]; then
    source "$ALERT_CONFIG"
fi

# Get trap information from environment variables
TRAP_TIME=$(date '+%Y-%m-%d %H:%M:%S')
SOURCE_IP="${SNMP_TRANSPORT_ADDRESS}"
OID="${SNMP_COMMAND}"
UPTIME="${SNMP_ARG2:-Unknown}"
TRAP_OID="${SNMP_ARG3:-Unknown}"

# Read all trap variables
TRAP_DATA=""
while read line; do
    TRAP_DATA+="$line\n"
done

# Log trap to file
echo "[$TRAP_TIME] Source: $SOURCE_IP, OID: $TRAP_OID" >> "$TRAP_LOG"
echo -e "$TRAP_DATA" >> "$TRAP_LOG"
echo "---" >> "$TRAP_LOG"

# Store in simple database for tracking
echo "$TRAP_TIME|$SOURCE_IP|$TRAP_OID|$(echo -e "$TRAP_DATA" | tr '\n' ' ')" >> "$TRAP_DB"

# Determine trap severity
SEVERITY="INFO"
case "$TRAP_OID" in
    *coldStart*|*warmStart*)
        SEVERITY="WARNING"
        ;;
    *linkDown*|*authenticationFailure*)
        SEVERITY="CRITICAL"
        ;;
    *linkUp*)
        SEVERITY="INFO"
        ;;
esac

# Send alerts based on severity
if [ "$SEVERITY" = "CRITICAL" ] || [ "$SEVERITY" = "WARNING" ]; then
    /etc/snmp/traphandlers/send_alert.sh "$SEVERITY" "$SOURCE_IP" "$TRAP_OID" "$TRAP_DATA"
fi

exit 0
sudo chmod 755 /etc/snmp/traphandlers/default_handler.sh

Create specialized trap handlers

Create specific handlers for different types of network events with targeted processing logic.

#!/bin/bash

# System Event Trap Handler (coldStart, warmStart)

TRAP_LOG="/var/log/snmp/traps/system.log"
SOURCE_IP="${SNMP_TRANSPORT_ADDRESS}"
TRAP_TIME=$(date '+%Y-%m-%d %H:%M:%S')

# Read trap data
TRAP_DATA=""
while read line; do
    TRAP_DATA+="$line\n"
done

# Determine event type
EVENT_TYPE="System Event"
if [[ "$SNMP_ARG3" == *"coldStart"* ]]; then
    EVENT_TYPE="System Cold Start"
elif [[ "$SNMP_ARG3" == *"warmStart"* ]]; then
    EVENT_TYPE="System Warm Start"
fi

# Log system event
echo "[$TRAP_TIME] $EVENT_TYPE from $SOURCE_IP" >> "$TRAP_LOG"
echo -e "$TRAP_DATA" >> "$TRAP_LOG"
echo "---" >> "$TRAP_LOG"

# Trigger system event alert
/etc/snmp/traphandlers/send_alert.sh "WARNING" "$SOURCE_IP" "$EVENT_TYPE" "Device restarted: $TRAP_DATA"

exit 0
#!/bin/bash

# Interface Event Trap Handler (linkUp, linkDown)

TRAP_LOG="/var/log/snmp/traps/interface.log"
SOURCE_IP="${SNMP_TRANSPORT_ADDRESS}"
TRAP_TIME=$(date '+%Y-%m-%d %H:%M:%S')

# Read trap data
TRAP_DATA=""
INTERFACE_ID="Unknown"
while read line; do
    TRAP_DATA+="$line\n"
    # Extract interface ID if present
    if [[ "$line" == *"ifIndex"* ]]; then
        INTERFACE_ID=$(echo "$line" | grep -o '[0-9]\+' | head -1)
    fi
done

# Determine link status
LINK_STATUS="Unknown"
SEVERITY="INFO"
if [[ "$SNMP_ARG3" == *"linkDown"* ]]; then
    LINK_STATUS="Link Down"
    SEVERITY="CRITICAL"
elif [[ "$SNMP_ARG3" == *"linkUp"* ]]; then
    LINK_STATUS="Link Up"
    SEVERITY="INFO"
fi

# Log interface event
echo "[$TRAP_TIME] $LINK_STATUS on interface $INTERFACE_ID from $SOURCE_IP" >> "$TRAP_LOG"
echo -e "$TRAP_DATA" >> "$TRAP_LOG"
echo "---" >> "$TRAP_LOG"

# Send alert for link down events
if [ "$SEVERITY" = "CRITICAL" ]; then
    /etc/snmp/traphandlers/send_alert.sh "$SEVERITY" "$SOURCE_IP" "Interface Down" "Interface $INTERFACE_ID is down on device $SOURCE_IP"
fi

exit 0
#!/bin/bash

# Security Event Trap Handler (authenticationFailure)

TRAP_LOG="/var/log/snmp/traps/security.log"
SOURCE_IP="${SNMP_TRANSPORT_ADDRESS}"
TRAP_TIME=$(date '+%Y-%m-%d %H:%M:%S')

# Read trap data
TRAP_DATA=""
while read line; do
    TRAP_DATA+="$line\n"
done

# Log security event
echo "[$TRAP_TIME] SECURITY ALERT: Authentication failure from $SOURCE_IP" >> "$TRAP_LOG"
echo -e "$TRAP_DATA" >> "$TRAP_LOG"
echo "---" >> "$TRAP_LOG"

# Always send critical alert for security events
/etc/snmp/traphandlers/send_alert.sh "CRITICAL" "$SOURCE_IP" "Authentication Failure" "SNMP authentication failure detected from $SOURCE_IP"

exit 0
sudo chmod 755 /etc/snmp/traphandlers/*.sh

Create alert configuration and sender script

Configure email and webhook alert settings with the alert dispatch script.

# SNMP Trap Alert Configuration

# Email settings
EMAIL_ENABLED=true
EMAIL_TO="admin@example.com"
EMAIL_FROM="snmp-monitor@example.com"
EMAIL_SUBJECT_PREFIX="[SNMP Alert]"

# Webhook settings
WEBHOOK_ENABLED=true
WEBHOOK_URL="https://hooks.example.com/snmp-alerts"
WEBHOOK_SECRET="your-webhook-secret-here"

# Slack webhook (optional)
SLACK_ENABLED=false
SLACK_WEBHOOK_URL="https://hooks.slack.com/services/YOUR/SLACK/WEBHOOK"

# Alert throttling (seconds between duplicate alerts)
ALERT_THROTTLE=300

# Log settings
ALERT_LOG="/var/log/snmp/traps/alerts.log"
#!/bin/bash

# SNMP Trap Alert Sender
# Sends alerts via email, webhook, and other channels

ALERT_CONFIG="/etc/snmp/alert_config.conf"
THROTTLE_FILE="/var/lib/snmp/trapdb/alert_throttle"

# Source configuration
if [ -f "$ALERT_CONFIG" ]; then
    source "$ALERT_CONFIG"
else
    echo "Alert configuration not found: $ALERT_CONFIG"
    exit 1
fi

SEVERITY="$1"
SOURCE_IP="$2"
EVENT_TYPE="$3"
MESSAGE="$4"
TIMESTAMP=$(date '+%Y-%m-%d %H:%M:%S')

# Throttle duplicate alerts
ALERT_KEY="${SOURCE_IP}_${EVENT_TYPE}"
if [ -f "$THROTTLE_FILE" ]; then
    LAST_ALERT=$(grep "^$ALERT_KEY" "$THROTTLE_FILE" | cut -d'|' -f2)
    if [ -n "$LAST_ALERT" ]; then
        TIME_DIFF=$(($(date +%s) - $LAST_ALERT))
        if [ $TIME_DIFF -lt $ALERT_THROTTLE ]; then
            echo "[$TIMESTAMP] Alert throttled: $ALERT_KEY" >> "$ALERT_LOG"
            exit 0
        fi
    fi
fi

# Update throttle file
grep -v "^$ALERT_KEY" "$THROTTLE_FILE" 2>/dev/null > "${THROTTLE_FILE}.tmp" || touch "${THROTTLE_FILE}.tmp"
echo "$ALERT_KEY|$(date +%s)" >> "${THROTTLE_FILE}.tmp"
mv "${THROTTLE_FILE}.tmp" "$THROTTLE_FILE"

# Log alert
echo "[$TIMESTAMP] Sending $SEVERITY alert for $SOURCE_IP: $EVENT_TYPE" >> "$ALERT_LOG"

# Send email alert
if [ "$EMAIL_ENABLED" = "true" ]; then
    EMAIL_BODY="SNMP Trap Alert\n\nSeverity: $SEVERITY\nSource: $SOURCE_IP\nEvent: $EVENT_TYPE\nTime: $TIMESTAMP\n\nDetails:\n$MESSAGE"
    echo -e "$EMAIL_BODY" | mail -s "$EMAIL_SUBJECT_PREFIX $SEVERITY - $EVENT_TYPE from $SOURCE_IP" "$EMAIL_TO"
fi

# Send webhook alert
if [ "$WEBHOOK_ENABLED" = "true" ] && [ -n "$WEBHOOK_URL" ]; then
    WEBHOOK_PAYLOAD=$(cat <
`sudo chmod 755 /etc/snmp/traphandlers/send_alert.sh`

Configure Nagios integration

Create Nagios passive check integration for SNMP trap events.

`#!/bin/bash

# Nagios SNMP Trap Integration
# Sends passive check results to Nagios based on trap events

NAGIOS_COMMAND_FILE="/var/lib/nagios3/rw/nagios.cmd"
NAGIOS_CONFIG="/etc/snmp/nagios_trap_config.conf"

# Source Nagios configuration
if [ -f "$NAGIOS_CONFIG" ]; then
    source "$NAGIOS_CONFIG"
else
    # Default settings
    NAGIOS_ENABLED=false
    NAGIOS_SERVICE_PREFIX="SNMP_"
fi

if [ "$NAGIOS_ENABLED" != "true" ]; then
    exit 0
fi

SOURCE_IP="$1"
EVENT_TYPE="$2"
SEVERITY="$3"
MESSAGE="$4"

# Map severity to Nagios states
NAGIOS_STATE=0
case "$SEVERITY" in
    "CRITICAL") NAGIOS_STATE=2 ;;
    "WARNING") NAGIOS_STATE=1 ;;
    "INFO") NAGIOS_STATE=0 ;;
esac

# Create service name
SERVICE_NAME="${NAGIOS_SERVICE_PREFIX}${EVENT_TYPE}"

# Map IP to hostname if configured
HOSTNAME="$SOURCE_IP"
if [ -f "/etc/snmp/ip_hostname_map.conf" ]; then
    MAPPED_HOST=$(grep "^$SOURCE_IP" /etc/snmp/ip_hostname_map.conf | cut -d' ' -f2)
    if [ -n "$MAPPED_HOST" ]; then
        HOSTNAME="$MAPPED_HOST"
    fi
fi

# Submit passive check result
TIMESTAMP=$(date +%s)
echo "[$TIMESTAMP] PROCESS_SERVICE_CHECK_RESULT;$HOSTNAME;$SERVICE_NAME;$NAGIOS_STATE;$MESSAGE" >> "$NAGIOS_COMMAND_FILE"

exit 0`
`# Nagios SNMP Trap Integration Configuration

NAGIOS_ENABLED=true
NAGIOS_SERVICE_PREFIX="SNMP_"

# Command file location (check your Nagios installation)
NAGIOS_COMMAND_FILE="/var/lib/nagios3/rw/nagios.cmd"`
`# IP to Hostname mapping for Nagios integration
# Format: IP_ADDRESS HOSTNAME
203.0.113.10 router-01
203.0.113.11 switch-01
203.0.113.12 server-01`
`sudo chmod 755 /etc/snmp/traphandlers/nagios_integration.sh`

Create Zabbix integration script

Build Zabbix integration for trap data using zabbix_sender utility.

`#!/bin/bash

# Zabbix SNMP Trap Integration
# Sends trap data to Zabbix server using zabbix_sender

ZABBIX_CONFIG="/etc/snmp/zabbix_trap_config.conf"

# Source Zabbix configuration
if [ -f "$ZABBIX_CONFIG" ]; then
    source "$ZABBIX_CONFIG"
else
    # Default settings
    ZABBIX_ENABLED=false
    ZABBIX_SERVER="127.0.0.1"
    ZABBIX_PORT=10051
fi

if [ "$ZABBIX_ENABLED" != "true" ]; then
    exit 0
fi

SOURCE_IP="$1"
EVENT_TYPE="$2"
SEVERITY="$3"
MESSAGE="$4"

# Map IP to Zabbix hostname if configured
ZABBIX_HOST="$SOURCE_IP"
if [ -f "/etc/snmp/zabbix_host_map.conf" ]; then
    MAPPED_HOST=$(grep "^$SOURCE_IP" /etc/snmp/zabbix_host_map.conf | cut -d' ' -f2)
    if [ -n "$MAPPED_HOST" ]; then
        ZABBIX_HOST="$MAPPED_HOST"
    fi
fi

# Create trap item key
ITEM_KEY="snmp.trap[${EVENT_TYPE}]"

# Send data to Zabbix
echo "$ZABBIX_HOST $ITEM_KEY $MESSAGE" | zabbix_sender -z "$ZABBIX_SERVER" -p "$ZABBIX_PORT" -T -i - >/dev/null 2>&1

# Send trap count metric
COUNT_KEY="snmp.trap.count[${EVENT_TYPE}]"
echo "$ZABBIX_HOST $COUNT_KEY 1" | zabbix_sender -z "$ZABBIX_SERVER" -p "$ZABBIX_PORT" -T -i - >/dev/null 2>&1

exit 0`
`# Zabbix SNMP Trap Integration Configuration

ZABBIX_ENABLED=true
ZABBIX_SERVER="203.0.113.100"
ZABBIX_PORT=10051`
`# IP to Zabbix Hostname mapping
# Format: IP_ADDRESS ZABBIX_HOSTNAME
203.0.113.10 Router-Office-01
203.0.113.11 Switch-Floor-01
203.0.113.12 Server-Web-01`

Install Zabbix sender utility

Install zabbix_sender for sending trap data to Zabbix server.

`sudo apt install -y zabbix-sender`
`sudo dnf install -y zabbix-sender`

Update trap handlers with integrations

Modify the main trap handlers to call monitoring system integrations.

`sudo cp /etc/snmp/traphandlers/default_handler.sh /etc/snmp/traphandlers/default_handler.sh.backup`
`#!/bin/bash

# Enhanced Default SNMP Trap Handler with Monitoring Integration

TRAP_LOG="/var/log/snmp/traps/default.log"
ALERT_CONFIG="/etc/snmp/alert_config.conf"
TRAP_DB="/var/lib/snmp/trapdb/traps.db"

# Source alerting configuration
if [ -f "$ALERT_CONFIG" ]; then
    source "$ALERT_CONFIG"
fi

# Get trap information from environment variables
TRAP_TIME=$(date '+%Y-%m-%d %H:%M:%S')
SOURCE_IP="${SNMP_TRANSPORT_ADDRESS}"
OID="${SNMP_COMMAND}"
UPTIME="${SNMP_ARG2:-Unknown}"
TRAP_OID="${SNMP_ARG3:-Unknown}"

# Read all trap variables
TRAP_DATA=""
while read line; do
    TRAP_DATA+="$line\n"
done

# Log trap to file
echo "[$TRAP_TIME] Source: $SOURCE_IP, OID: $TRAP_OID" >> "$TRAP_LOG"
echo -e "$TRAP_DATA" >> "$TRAP_LOG"
echo "---" >> "$TRAP_LOG"

# Store in simple database for tracking
echo "$TRAP_TIME|$SOURCE_IP|$TRAP_OID|$(echo -e "$TRAP_DATA" | tr '\n' ' ')" >> "$TRAP_DB"

# Determine trap severity and event type
SEVERITY="INFO"
EVENT_TYPE="Generic"
case "$TRAP_OID" in
    *coldStart*)
        SEVERITY="WARNING"
        EVENT_TYPE="ColdStart"
        ;;
    *warmStart*)
        SEVERITY="WARNING"
        EVENT_TYPE="WarmStart"
        ;;
    *linkDown*)
        SEVERITY="CRITICAL"
        EVENT_TYPE="LinkDown"
        ;;
    *linkUp*)
        SEVERITY="INFO"
        EVENT_TYPE="LinkUp"
        ;;
    *authenticationFailure*)
        SEVERITY="CRITICAL"
        EVENT_TYPE="AuthFailure"
        ;;
esac

# Send alerts based on severity
if [ "$SEVERITY" = "CRITICAL" ] || [ "$SEVERITY" = "WARNING" ]; then
    /etc/snmp/traphandlers/send_alert.sh "$SEVERITY" "$SOURCE_IP" "$EVENT_TYPE" "$TRAP_DATA"
fi

# Send to monitoring systems
/etc/snmp/traphandlers/nagios_integration.sh "$SOURCE_IP" "$EVENT_TYPE" "$SEVERITY" "$(echo -e "$TRAP_DATA" | head -1)" &
/etc/snmp/traphandlers/zabbix_integration.sh "$SOURCE_IP" "$EVENT_TYPE" "$SEVERITY" "$(echo -e "$TRAP_DATA" | head -1)" &

exit 0`

Configure systemd service

Create and configure the systemd service for snmptrapd with proper se

Automated install script

Run this to automate the entire setup

#snmp #trap #monitoring #alerting #nagios

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