Configure Nagios SNMP monitoring for network devices with automated discovery and templates

Install SNMP utilities and MIB libraries

Install the necessary SNMP tools and Management Information Base (MIB) libraries for querying network devices.

sudo apt update
sudo apt install -y snmp snmp-mibs-downloader libsnmp-perl

sudo dnf install -y net-snmp net-snmp-utils net-snmp-perl

Download and configure MIB files

Download standard MIB files and configure SNMP to use them for better device identification and monitoring.

sudo download-mibs
sudo sed -i 's/^mibs :/# mibs :/' /etc/snmp/snmp.conf

sudo mkdir -p /usr/share/snmp/mibs
sudo wget -O /usr/share/snmp/mibs/RFC1213-MIB http://www.iana.org/assignments/ianaiftype-mib/ianaiftype-mib

Test SNMP connectivity to network devices

Verify SNMP communication with your network devices before configuring Nagios monitoring.

snmpwalk -v2c -c public 203.0.113.10 1.3.6.1.2.1.1.1.0
snmpget -v2c -c public 203.0.113.10 1.3.6.1.2.1.1.5.0

Create SNMP command definitions

Define reusable SNMP commands in Nagios for common network monitoring tasks.

# SNMP System Information
define command{
    command_name    check_snmp_system
    command_line    $USER1$/check_snmp -H $HOSTADDRESS$ -C $ARG1$ -o 1.3.6.1.2.1.1.3.0 -w $ARG2$ -c $ARG3$
}

SNMP Interface Status
define command{
    command_name    check_snmp_interface
    command_line    $USER1$/check_snmp -H $HOSTADDRESS$ -C $ARG1$ -o 1.3.6.1.2.1.2.2.1.8.$ARG2$ -r 1 -w 1 -c 1
}

SNMP Interface Utilization
define command{
    command_name    check_snmp_interface_util
    command_line    $USER1$/check_snmp -H $HOSTADDRESS$ -C $ARG1$ -o 1.3.6.1.2.1.2.2.1.10.$ARG2$,1.3.6.1.2.1.2.2.1.16.$ARG2$ -w $ARG3$ -c $ARG4$
}

SNMP CPU Utilization
define command{
    command_name    check_snmp_cpu
    command_line    $USER1$/check_snmp -H $HOSTADDRESS$ -C $ARG1$ -o 1.3.6.1.4.1.9.9.109.1.1.1.1.7.1 -w $ARG2$ -c $ARG3$
}

SNMP Memory Utilization
define command{
    command_name    check_snmp_memory
    command_line    $USER1$/check_snmp -H $HOSTADDRESS$ -C $ARG1$ -o 1.3.6.1.4.1.9.9.48.1.1.1.5.1,1.3.6.1.4.1.9.9.48.1.1.1.6.1 -w $ARG2$ -c $ARG3$
}

Create network device host template

Define a reusable host template for network devices with common SNMP monitoring settings.

# Generic Network Device Template
define host{
    name                    generic-network-device
    use                     generic-host
    check_period            24x7
    check_interval          5
    retry_interval          1
    max_check_attempts      10
    check_command           check-host-alive
    notification_period     24x7
    notification_interval   30
    notification_options    d,u,r
    contact_groups          admins
    register                0
}

Switch Template
define host{
    name                    switch-template
    use                     generic-network-device
    hostgroups              switches
    icon_image             switch.png
    vrml_image             switch.png
    statusmap_image        switch.gd2
    register               0
}

Router Template
define host{
    name                    router-template
    use                     generic-network-device
    hostgroups              routers
    icon_image             router.png
    vrml_image             router.png
    statusmap_image        router.gd2
    register               0
}

Create service templates for SNMP monitoring

Define service templates for common network device monitoring tasks.

# SNMP Service Template
define service{
    name                    generic-snmp-service
    use                     generic-service
    check_interval          5
    retry_interval          1
    max_check_attempts      3
    notification_interval   30
    register                0
}

Network Interface Service Template
define service{
    name                    network-interface-service
    use                     generic-snmp-service
    normal_check_interval   2
    retry_check_interval    1
    register                0
}

Create host groups for network devices

Organize network devices into logical groups for easier management and monitoring.

# Network Device Host Groups
define hostgroup{
    hostgroup_name  switches
    alias           Network Switches
    members
}

define hostgroup{
    hostgroup_name  routers
    alias           Network Routers
    members
}

define hostgroup{
    hostgroup_name  firewalls
    alias           Network Firewalls
    members
}

define hostgroup{
    hostgroup_name  wireless-aps
    alias           Wireless Access Points
    members
}

Configure network devices for monitoring

Create individual host definitions for your network devices using the templates.

# Core Switch
define host{
    use                 switch-template
    host_name           core-switch-01
    alias               Core Switch 01
    address             203.0.113.10
    hostgroups          switches
    parents
}

Access Switch
define host{
    use                 switch-template
    host_name           access-switch-01
    alias               Access Switch 01
    address             203.0.113.11
    hostgroups          switches
    parents             core-switch-01
}

Border Router
define host{
    use                 router-template
    host_name           border-router-01
    alias               Border Router 01
    address             203.0.113.1
    hostgroups          routers
    parents
}

Configure SNMP services for network devices

Define specific SNMP monitoring services for each type of network device.

# System Uptime Monitoring
define service{
    use                     generic-snmp-service
    host_name               core-switch-01,access-switch-01,border-router-01
    service_description     System Uptime
    check_command           check_snmp_system!public!100000!50000
}

Interface Status Monitoring (GigabitEthernet1/0/1)
define service{
    use                     network-interface-service
    host_name               core-switch-01
    service_description     Interface Gi1/0/1 Status
    check_command           check_snmp_interface!public!1
}

Interface Status Monitoring (GigabitEthernet1/0/2)
define service{
    use                     network-interface-service
    host_name               core-switch-01
    service_description     Interface Gi1/0/2 Status
    check_command           check_snmp_interface!public!2
}

CPU Utilization (Cisco devices)
define service{
    use                     generic-snmp-service
    host_name               border-router-01
    service_description     CPU Utilization
    check_command           check_snmp_cpu!public!80!95
}

Memory Utilization (Cisco devices)
define service{
    use                     generic-snmp-service
    host_name               border-router-01
    service_description     Memory Utilization
    check_command           check_snmp_memory!public!80!95
}

Create automated device discovery script

Implement a script for automated discovery of SNMP-enabled devices on your network.

#!/bin/bash

SNMP Network Device Discovery Script
Usage: ./snmp_discovery.sh network_range community_string

NETWORK_RANGE=${1:-"203.0.113.0/24"}
COMMUNITY=${2:-"public"}
OUTPUT_FILE="/tmp/discovered_devices.txt"
CONFIG_FILE="/usr/local/nagios/etc/objects/discovered-devices.cfg"

echo "Starting SNMP device discovery on network: $NETWORK_RANGE"
echo "Using community string: $COMMUNITY"

Clear previous results
> $OUTPUT_FILE
> $CONFIG_FILE

Scan network range for SNMP devices
nmap -sU -p 161 --open $NETWORK_RANGE | grep -E "^Nmap scan report" | awk '{print $5}' > /tmp/potential_devices.txt

while read -r ip; do
    # Test SNMP connectivity
    sysname=$(snmpget -v2c -c $COMMUNITY -t 2 -r 1 $ip 1.3.6.1.2.1.1.5.0 2>/dev/null | awk -F'STRING: ' '{print $2}' | tr -d '"')
    sysdesc=$(snmpget -v2c -c $COMMUNITY -t 2 -r 1 $ip 1.3.6.1.2.1.1.1.0 2>/dev/null | awk -F'STRING: ' '{print $2}' | tr -d '"')
    
    if [ ! -z "$sysname" ]; then
        echo "$ip|$sysname|$sysdesc" >> $OUTPUT_FILE
        echo "Found device: $ip - $sysname"
        
        # Generate basic Nagios configuration
        hostname=$(echo $sysname | tr ' ' '-' | tr '[:upper:]' '[:lower:]')
        
        echo "# Auto-discovered device: $sysname" >> $CONFIG_FILE
        echo "define host{" >> $CONFIG_FILE
        echo "    use                 generic-network-device" >> $CONFIG_FILE
        echo "    host_name           $hostname" >> $CONFIG_FILE
        echo "    alias               $sysname" >> $CONFIG_FILE
        echo "    address             $ip" >> $CONFIG_FILE
        echo "    hostgroups          discovered-devices" >> $CONFIG_FILE
        echo "}" >> $CONFIG_FILE
        echo "" >> $CONFIG_FILE
        
        # Add basic SNMP service
        echo "define service{" >> $CONFIG_FILE
        echo "    use                     generic-snmp-service" >> $CONFIG_FILE
        echo "    host_name               $hostname" >> $CONFIG_FILE
        echo "    service_description     System Uptime" >> $CONFIG_FILE
        echo "    check_command           check_snmp_system!$COMMUNITY!100000!50000" >> $CONFIG_FILE
        echo "}" >> $CONFIG_FILE
        echo "" >> $CONFIG_FILE
    fi
done < /tmp/potential_devices.txt

echo "Discovery complete. Found $(wc -l < $OUTPUT_FILE) SNMP devices."
echo "Configuration written to: $CONFIG_FILE"
echo "Please review and restart Nagios to apply changes."

Make discovery script executable and create hostgroup

Set proper permissions for the discovery script and create a hostgroup for discovered devices.

sudo chmod 755 /usr/local/nagios/libexec/snmp_discovery.sh
sudo chown nagios:nagios /usr/local/nagios/libexec/snmp_discovery.sh

# Add this to your existing hostgroups configuration
define hostgroup{
    hostgroup_name  discovered-devices
    alias           Auto-discovered Network Devices
    members
}

Create interface monitoring script

Implement automated interface discovery and monitoring for network devices.

#!/bin/bash

Network Interface Discovery Script
Usage: ./interface_discovery.sh device_ip community_string

DEVICE_IP=$1
COMMUNITY=$2
OUTPUT_FILE="/tmp/interfaces_${DEVICE_IP}.cfg"

if [ -z "$DEVICE_IP" ] || [ -z "$COMMUNITY" ]; then
    echo "Usage: $0  "
    exit 1
fi

echo "Discovering interfaces on device: $DEVICE_IP"

Clear previous results
> $OUTPUT_FILE

Get interface information
snmpwalk -v2c -c $COMMUNITY $DEVICE_IP 1.3.6.1.2.1.2.2.1.2 2>/dev/null | while read line; do
    interface_index=$(echo $line | awk -F'.' '{print $NF}' | awk '{print $1}')
    interface_name=$(echo $line | awk -F'STRING: ' '{print $2}' | tr -d '"')
    
    # Skip loopback and null interfaces
    if [[ $interface_name == "Loopback" ]] || [[ $interface_name == "Null" ]]; then
        continue
    fi
    
    # Get interface operational status
    oper_status=$(snmpget -v2c -c $COMMUNITY $DEVICE_IP 1.3.6.1.2.1.2.2.1.8.$interface_index 2>/dev/null | awk '{print $NF}')
    admin_status=$(snmpget -v2c -c $COMMUNITY $DEVICE_IP 1.3.6.1.2.1.2.2.1.7.$interface_index 2>/dev/null | awk '{print $NF}')
    
    if [ ! -z "$interface_name" ] && [ "$admin_status" == "1" ]; then
        service_name=$(echo "Interface $interface_name Status" | sed 's/[^a-zA-Z0-9 ]/_/g')
        hostname=$(snmpget -v2c -c $COMMUNITY $DEVICE_IP 1.3.6.1.2.1.1.5.0 2>/dev/null | awk -F'STRING: ' '{print $2}' | tr -d '"' | tr ' ' '-' | tr '[:upper:]' '[:lower:]')
        
        echo "# Interface: $interface_name (Index: $interface_index)" >> $OUTPUT_FILE
        echo "define service{" >> $OUTPUT_FILE
        echo "    use                     network-interface-service" >> $OUTPUT_FILE
        echo "    host_name               $hostname" >> $OUTPUT_FILE
        echo "    service_description     $service_name" >> $OUTPUT_FILE
        echo "    check_command           check_snmp_interface!$COMMUNITY!$interface_index" >> $OUTPUT_FILE
        echo "}" >> $OUTPUT_FILE
        echo "" >> $OUTPUT_FILE
        
        echo "Found interface: $interface_name (Index: $interface_index)"
    fi
done

echo "Interface discovery complete for $DEVICE_IP"
echo "Configuration written to: $OUTPUT_FILE"

Make interface discovery script executable

Set proper permissions for the interface discovery script.

sudo chmod 755 /usr/local/nagios/libexec/interface_discovery.sh
sudo chown nagios:nagios /usr/local/nagios/libexec/interface_discovery.sh

Update main Nagios configuration

Include the new configuration files in the main Nagios configuration.

# Add these lines to include SNMP monitoring configurations
cfg_file=/usr/local/nagios/etc/objects/network-devices.cfg
cfg_file=/usr/local/nagios/etc/objects/network-services.cfg
cfg_file=/usr/local/nagios/etc/objects/discovered-devices.cfg
cfg_file=/usr/local/nagios/etc/objects/hostgroups.cfg

Validate configuration and restart Nagios

Check the Nagios configuration for syntax errors and restart the service.

sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
sudo systemctl restart nagios
sudo systemctl status nagios