Nagios Quickstart

Quick Start: Monitor a Cisco Router with Nagios
This quickstart assumes you are one of those that cannot stand to read directions and hope to find the answers quickly.  Note: this assumes you have a working Nagios server.

Install the Necessary SNMP Programs
The first thing you want to do is check what packages are available for Centos or the distribution that you are using.  These packages often get the names changed so it is hard to know if they are in the repository.

yum list | grep snmp
cluster-snmp.i386                        0.12.0-7.el5.centos    base            
net-snmp.i386                            1:5.3.1-24.el5_2.2     updates         
net-snmp-devel.i386                      1:5.3.1-24.el5_2.2     updates         
net-snmp-libs.i386                       1:5.3.1-24.el5_2.2     updates         
net-snmp-perl.i386                       1:5.3.1-24.el5_2.2     updates         
net-snmp-utils.i386                      1:5.3.1-24.el5_2.2     updates         
php-snmp.i386                            5.1.6-20.el5_2.1       updates         
snmpbrowser.i386                         0.4-2.el5.rf           rpmforge


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


Configure the Router
This is example is using minicom from a Linux machine.

minicom com1

config t

Router(config)#int e0
Router(config)#ip address 150.50.4.1 255.255.254.0
Router(config)#no shut

Router(config)#snmp-server community public ro       
Router(config)#access-list 60 permit 192.168.5.103  

Use snmpwalk to locate MIBs
snmpwalk is installed as one of the utilities above.  This is an invaluable took in setting up monitoring.

snmpwalk -v1 -c public 192.168.5.221  | less

In this whole string of MIBs, you will want to discover the name of your Ethernet port so you can monitor it.  Each vendor will have a different name, here it is "Ethernet0".

IF-MIB::ifDescr.1 = STRING: Ethernet0
IF-MIB::ifDescr.2 = STRING: Serial0
IF-MIB::ifDescr.3 = STRING: Serial1


Add Commands to /etc/nagios/objects/commands.cfg


# snmp Commands
define command{
command_name    check_ifstatus
command_line    $USER1$/check_ifstatus -H $HOSTADDRESS$ -C public -x $ARG1$
}
# Check iftraffic.pl
define command{
command_name check_iftraffic
command_line    $USER1$/check_iftraffic.pl -H $HOSTADDRESS$ -C $USER3$ -i $ARG1$ -b $ARG2$ -u m
}


Edit /etc/nagios/objects/routers.cfg
Make sure your path to this file is confiured in your /etc/nagios.cfg file.

Add the cisco host.

define host{
use             generic-switch
host_name       cisco2500
alias           cisco router
address         192.168.5.221
}


define service{
use             generic-service
host_name       cisco2500
service_description     Uptime
check_command           check_snmp!-C public -o sysUpTime.0
}
define service{
use             generic-service
host_name       cisco2500
service_description     interfaces
check_command           check_ifstatus!1
}
define service{
use             generic-service
host_name       cisco2500
service_description     PING
check_command           check_ping!200.0,20%!600.0,60%
normal_check_interval   5
retry_check_interval    1
}

Restart Nagios....fix the problems.