Nagios: Monitoring Router/Switch


1) Install prerequisites.

yum install -y net-snmp net-snmp-utils

2) Check to see whether ‘check_snmp’ and ‘check_mrtgtraf’ can be found under /usr/local/nagios/libexec/ folder. If not,  you need to reinstall the nagios-plugin.  (It can be found in my previous post on the Nagios Installation)

3) As the ‘check_mrtgtraf’ will retrieve the bandwidth utilization information from MRTG log, the MRTG has to been install.

yum install -y mrtg


mkdir /home/httpd/mrtg/


cfgmaker --global 'WorkDir: /home/httpd/mrtg' --output /etc/mrtg/dlink.cfg public@

/usr/bin/mrtg /etc/mrtg/dlink.cfg --loging /var/log/mrtg.log


#Edit the crontab file to make MRTG run every 5 minutes:

crontab -e

*/5 * * * * /usr/bin/mrtg /etc/mrtg/dlink.cfg --logging /var/log/mrtg.log



4) Modify ‘switch.cfg’ file to customize the host and its interface that you want to monitor.

vi /usr/local/nagios/etc/objects/switch.cfg


  • Change IP address in the host definition
  • Change every host_name to the switch name that you want to monitor
  • Find ‘# Monitor bandwidth via MRTG logs’ and change the MRTG log to fit your conditions.

check_command           check_local_mrtgtraf!/home/httpd/mrtg/!AVG!1000000,1000000!5000000,5000000!10


5) Modify the ‘nagios.cfg’ file.

vi /usr/local/nagios/etc/nagios.cfg

uncomment ‘cfg_file=/usr/local/nagios/etc/objects/switch.cfg’

6) Verify the nagios configuration file then reload the nagios service if it is correct.



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