Centos Install and Configure MRTG

How do I install and configure MRTG under Fedora Linux or CentOS Linux v5.x server to monitor the traffic load on network-links including routers?

The Multi Router Traffic Grapher (MRTG) is a tool to monitor the traffic load on network-links.

MRTG generates HTML pages containing PNG images which provide a LIVE visual representation of this traffic. You need the following packages:

• mrtg : Multi Router Traffic Grapher
• net-snmp and net-snmp-utils : SNMP (Simple Network Management Protocol) is a protocol used for network management. The NET-SNMP project includes various SNMP tools. net-snmp package contains the snmpd and snmptrapd daemons, documentation, etc. You also want to install the net-snmp-utils package, which contains NET-SNMP utilities.

This FAQ works with RHEL / CentOS and Fedora Linux.

Step # 1: Install MRTG

Type the following command to install packages using yum command under CentOS / Fedora Linux:
# yum install mrtg net-snmp net-snmp-utils

Step # 2: Configure snmpd

If you need to monitor localhost including interface and other stuff such as CPU, memory etc, configure snmpd. Open /etc/snmp/snmpd.conf, enter:
# vi /etc/snmp/snmpd.conf
Update it as follows to only allow access from localhost:

com2sec local     localhost           public
group MyRWGroup v1         local
group MyRWGroup v2c        local
group MyRWGroup usm        local
view all    included  .1                               80
access MyRWGroup ""      any       noauth    exact  all    all    none
syslocation VSNL, India
syscontact Root <vivek@nixcraft.tld>

Save and close the file. Restart snmpd:
# chkconfig snmpd on
# service snmpd restart
Make sure you see interface IP, by running the following command:
# snmpwalk -v 1 -c public localhost IP-MIB::ipAdEntIfIndex
Sample Outputs:

IP-MIB::ipAdEntIfIndex.123.xx.yy.zzz = INTEGER: 2
IP-MIB::ipAdEntIfIndex.127.0.0.1 = INTEGER: 1

Step # 3: Configure MRTG

Use cfgmaker command to creates /etc/mrtg/mrtg.cfg file, enter:
# cfgmaker --global 'WorkDir: /var/www/mrtg' --output /etc/mrtg/mrtg.cfg public@localhost

• --global 'WorkDir: /var/www/mrtg' : add global config entries i.e. set workdir to store MRTG graphs.
• --output /etc/mrtg/mrtg.cfg: configr output filename
• public@localhost : public is the community name of the device you want to create a configuration for. If you are using the wrong community name you will get no response from the device. localhost is the DNS name or the IP number of an SNMP-managable device i.e. our local server.

Finally, run indexmaker to create web pages which display the status of an array of mrtg interface status pages:
# indexmaker --output=/var/www/mrtg/index.html /etc/mrtg/mrtg.cfg

Step # 4: Verify Cron Job

/etc/cron.d/mrtg runs mrtg command to monitor the traffic load on network links:
# cat /etc/cron.d/mrtg
Sample Output:

*/5 * * * * root LANG=C LC_ALL=C /usr/bin/mrtg /etc/mrtg/mrtg.cfg --lock-file /var/lock/mrtg/mrtg_l --confcache-file /var/lib/mrtg/mrtg.ok

Just make sure crond is running and you are done with configuration:
# chkconfig --list crond
If it is off in run level # 3, just run the following to turn on crond service:
# chkconfig crond on
# service crond on

How do I view mrtg graphs?

You need Apache web server to view graphs, simply type the following to install httpd:
# yum install httpd
# chkconfig httpd on
# service httpd on
Fire a webbrowser and type the url:
http://your-ip.add.ress/mrtg/
http://192.168.1.5/mrtg/

Fig.01:Sample MRTG Graph

How Do I Create MRTG For My Router at 192.168.1.254?

Run cfgmaker as follows (there is no need to configure snmp for router, as most router and switches comes pre configured with their own SNMPD):
# cfgmaker --global 'WorkDir: /var/www/mrtg' --output /etc/mrtg/mrtg.cfg public@router
OR
# cfgmaker --global 'WorkDir: /var/www/mrtg' --output /etc/mrtg/mrtg.cfg public@192.168.1.254