I use Nagios intensively and it gives me peace of mind knowing that I will get an alert on my phone, when there is a problem. More than that, if warning levels are setup properly, Nagios will proactively alert you before a problem becomes critical.
Earlier I wrote about, how to setup Nagios to monitor Linux Host, Windows Host and VPN device.
In this article, I’ll explain how to configure Nagios to monitor network switch and it’s active ports.
1. Enable switch.cfg in nagios.cfg
Uncomment the switch.cfg line in /usr/local/nagios/etc/nagios.cfg as shown below.<!-- @page { margin: 0.79in } P { margin-bottom: 0.08in } PRE.cjk { font-family: "DejaVu LGC Sans Mono", monospace } -->
[nagios-server]# grep switch.cfg /usr/local/nagios/etc/nagios.cfg cfg_file=/usr/local/nagios/etc/objects/switch.cfg
2. Add new hostgroup for switches in switch.cfg
Add the following switches hostgroup to the /usr/local/nagios/etc/objects/switch.cfg file.define hostgroup{ hostgroup_name switches alias Network Switches }
3. Add a new host for the switch to be monitered
In this example, I’ve defined a host to monitor the core switch in the /usr/local/nagios/etc/objects/switch.cfg file. Change the address directive to your switch ip-address accordingly.define host{ use generic-switch host_name core-switch alias Cisco Core Switch address 192.168.1.50 hostgroups switches }
4. Add common services for all switches
Displaying the uptime of the switch and verifying whether switch is alive are common services for all switches. So, define these services under the switches hostgroup_name as shown below.# Service definition to ping the switch using check_ping define service{ use generic-service hostgroup_name switches service_description PING check_command check_ping!200.0,20%!600.0,60% normal_check_interval 5 retry_check_interval 1 } # Service definition to monitor switch uptime using check_snmp define service{ use generic-service hostgroup_name switches service_description Uptime check_command check_snmp!-C public -o sysUpTime.0 }
5. Add service to monitor port bandwidth usage
check_local_mrtgtraf uses the Multil Router Traffic Grapher – MRTG. So, you need to install MRTG for this to work properly. The *.log file mentioned below should point to the MRTG log file on your system.define service{ use generic-service host_name core-switch service_description Port 1 Bandwidth Usage check_command check_local_mrtgtraf!/var/lib/mrtg/192.168.1.11_1.log!AVG!1000000,2000000!5000000,5000000!10 }
6. Add service to monitor an active switch port
Use check_snmp to monitor the specific port as shown below. The following two services monitors port#1 and port#5. To add additional ports, change the value ifOperStatus.n accordingly. i.e n defines the port#.<!-- google_ad_client = "pub-8090601437064582"; /* TGS Inside Content Big */ google_ad_slot = "8006040097"; google_ad_width = 336; google_ad_height = 280; //-->google_protectAndRun("ads_core.google_render_ad", google_handleError, google_render_ad);# Monitor status of port number 1 on the Cisco core switch define service{ use generic-service host_name core-switch service_description Port 1 Link Status check_command check_snmp!-C public -o ifOperStatus.1 -r 1 -m RFC1213-MIB } # Monitor status of port number 5 on the Cisco core switch define service{ use generic-service host_name core-switch service_description Port 5 Link Status check_command check_snmp!-C public -o ifOperStatus.5 -r 1 -m RFC1213-MIB }
7. Add services to monitor multiple switch ports together
Sometimes you may need to monitor the status of multiple ports combined together. i.e Nagios should send you an alert, even if one of the port is down. In this case, define the following service to monitor multiple ports.# Monitor ports 1 - 6 on the Cisco core switch. define service{ use generic-service host_name core-switch service_description Ports 1-6 Link Status check_command check_snmp!-C public -o ifOperStatus.1 -r 1 -m RFC1213-MIB, -o ifOperStatus.2 -r 1 -m RFC1213-MIB, -o ifOperStatus.3 -r 1 -m RFC1213-MIB, -o ifOperStatus.4 -r 1 -m RFC1213-MIB, -o ifOperStatus.5 -r 1 -m RFC1213-MIB, -o ifOperStatus.6 -r 1 -m RFC1213-MIB }
8. Validate configuration and restart nagios
Verify the nagios configuration to make sure there are no warnings and errors.# /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg Total Warnings: 0 Total Errors: 0 Things look okay - No serious problems were detected during the pre-flight checkRestart the nagios server to start monitoring the VPN device.
# /etc/rc.d/init.d/nagios stop Stopping nagios: .done. # /etc/rc.d/init.d/nagios start Starting nagios: done.Verify the status of the switch from the Nagios web UI: http://{nagios-server}/nagios as shown below:
Fig: Nagios GUI displaying status of a Network Switch
9. Troubleshooting
Issue1: Nagios GUI displays “check_mrtgtraf: Unable to open MRTG log file” error message for the Port bandwidth usageSolution1: make sure the *.log file defined in the check_local_mrtgtraf service is pointing to the correct location.
Issue2: Nagios UI displays “Return code of 127 is out of bounds – plugin may be missing” error message for Port Link Status.
Solution2: Make sure both net-snmp and net-snmp-util packages are installed. In my case, I was missing the net-snmp-utils package and installing it resolved this issue as shown below.
[nagios-server]# rpm -qa | grep net-snmp net-snmp-libs-5.1.2-11.el4_6.11.2 net-snmp-5.1.2-11.el4_6.11.2 [nagios-server]# rpm -ivh net-snmp-utils-5.1.2-11.EL4.10.i386.rpm Preparing... ########################################### [100%] 1:net-snmp-utils ########################################### [100%] [nagios-server]# rpm -qa | grep net-snmp net-snmp-libs-5.1.2-11.el4_6.11.2 net-snmp-5.1.2-11.el4_6.11.2 net-snmp-utils-5.1.2-11.EL4.10
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