How to add device for SNMP Trap Monitoring in Nagios

SNMP Trap is pretty like syslog. It sends error messages to the Network Management System(NMS) like Nagios. Nagios doesn’t support SNMP trap by default. There is a Nagios plugin called SNMPTT that translate the received SNMP trap to the Nagios console. To install SNMPTT on Nagios, I used this guide "How to recieve SNMP Trap in Nagios". Afterwhich, you may follow the steps below to load additional SNMP MIBS trap for each managed device.

1) Load and compile MIBS to Nagios
This is the command to compile MIBS to Nagios server:
snmpttconvertmib --in= --out=/etc/snmp/snmptt.conf. --exec='/usr/local/nagios/libexec/eventhandlers/submit_check_result $r TRAP 1'

It would be tedious if there are too many MIBs files. Therefore, I wrote a simple bash script called “loadMIBS to compile all the MIBS in a folder.
if [ $# -ne 2 ]; then
echo "loadMIBS 'folder' 'device'"
exit 1
fi
for file in $( ls $1 ); do
/usr/sbin/snmpttconvertmib --in=$1\/$file \
--out=/etc/snmp/snmptt.conf.$2 \
--exec='/usr/local/nagios/libexec/eventhandlers/submit_check_result $r TRAP 1'
echo "MIBS loaded in /etc/snmp/snmptt.conf.$2"
done

2) Inform SNMPTT on the newly compiled Files
Modify /etc/snmp/snmptt.ini to include the earlier files:

[TrapFiles]
snmptt_conf_files =
/etc/snmp/snmptt.conf.devicename1
/etc/snmp/snmptt.conf.devicename2
END

3) Add the new Device to Nagios configuration file
I have created a standard file to consolidate all SNMP Trap devices at /usr/local/nagios/etc/objects/snmptrap.cfg. Just follow the example below:

define host{
use windows-server ; Inherit default values from a template
host_name HostA
alias HostA
address xx.xx.xx.xx ; IP address of the host
}

define host{
use windows-server ; Inherit default values from a template
host_name HostB
alias HostB
address xx.xx.xx.xx ; IP address of the host
}

define hostgroup{
hostgroup_name snmp_group ; The name of the hostgroup
alias SNMP TRAP
members HostA, HostB
}

define service{
hostgroup_name snmp_group
use snmptrap-service
contact_groups netadmin ; Who to alert & contact
}

4) Define New TRAP service on Nagios
Separately, on the templates.cfg, I have added this SNMP trap service
# define snmp trap service for network
define service{
use generic-service
name snmptrap-service
check_command check-host-alive
service_description TRAP
passive_checks_enabled 1
register 0
is_volatile 1
check_period none
max_check_attempts 1
normal_check_interval 1
retry_check_interval 1
notification_interval 31536000
notification_options w
}

Red: Make sure that the service description must match the submit_check_result parameter i.e. TRAP in this case. Otherwise, Nagios won't be able to match the recieved snmp trap to the passive service.

5) Verifying New SNMP Trap Service

Restart Nagios service and generate a test snmp trap from your managed device. If you do not receive an alert (email and/or sms), do the following:

• Check that the snmp trap daemon is running i.e. ps -e | grep trap
• Check the snmptt log that the trap is received
• Click on the "Event Logs" of Nagios admin console. Check that the event handler "submit_check_result" is executed correctly.