Step # 1: Make sure snmp server installed

Step # 2: Determine if snmp server is running or not

Step # 3 Make sure snmp server configured properly

Step # 4 Install mrtg if not installed

Step # 5 Configure mrtg

Step # 6 First test run of mrtg

Step # 7: Create crontab entry so that mrtg graph / images get generated every 5 minutes Step

# 8: Block ports 161, 162 udp at firewall. Step

# 9: Optional protect your MRTG graphs/html pages with password protected directory

yum install net-snmp-utils net-snmp

up2date -v -i net-snmp-utils net-snmp

Run 'ps' command to see if snmp server is running or not:

ps -aux | grep snmp
or
lsof -i :199
or
netstat -natv | grep ':199'
or
service snmpd start

Install all the pakage in one commnad inline:

yum -y install net-snmp net-snmp-utils mrtg httpd

Configure SNMP This SNMP Configuration will be carried out in Linux server and client device as well.

Login to router Configure SNMP

Login to router Configure SNMP
>enable
Password:

Router# config t

Router(config)#
Router(config)# snmp-server community ArkIT RO

Router(config)#exit

Router#write memory 
Building configuration... 
[OK]

Linux Server SNMP configuration

# cp /etc/snmp/snmpd.conf /etc/snmp/snmpd.conf.bak
# rm -rf /etc/snmp/snmpd.conf
# vi /etc/snmp/snmpd.conf

###### Copy and Paste below config lines #####
rocommunity ArkIT localhost
rocommunity ArkIT 192.168.2.5

# Allow Systems Management Data Engine SNMP to connect to snmpd using SMUX
smuxpeer .1.3.6.1.4.1.674.10892.1
##### Done ####

Start and enable SNMP service

# systemctl start snmpd.service
# systemctl enable snmpd.service

Verify SNMP is working or not using snmpwalk command

# snmpwalk -v2c -c ArkIT 192.168.2.10 system

cfgmaker Configuration Generator

Generate mrtg configuration file using cfgmaker command, if you want monitor multiple devices generate multiple configuration files one file for one device

# cfgmaker --snmp-options=:::::2 --ifref=descr ifdesc=descr ArkIT@192.168.2.10 > /etc/mrtg/router.cfg

By using above command will scan remote router device and its available interfaces, generates the configuration file to /etc/mrtg/router.cfg. Now edit the config file and UN-comment Workdir and change the path (if you want to change to another path) and also UN-comment Options if you want graph data in bits instead of bytes

Workdir: /var/www/html/mrtgOptions[_]: growright, bits

Now check config file is working as expected, below command will run in loop and generate all the html files and PNG files in Work directory location

for ((i=1; i <= 3; i++ )); do env LANG=C mrtg /etc/mrtg/router.cfg; done

Creates index files for mrtg web sites use indexmaker command

indexmaker --columns=1 /etc/mrtg/router.cfg > /var/www/html/index.html/index.html

Allow/Deny Web Page

# vi /etc/http/conf.d/mrtg.conf

Alias /mrtg /var/www/html/mrtg

<Location /mrtg>
Order deny,allow
Deny from all
Allow from 127.0.0.1
Allow from 192.168.2.0/24
</Location>

As per the above rule you can only access web page from 192.168.2.x IP addresses, if you want to allow all other networks to access web page specify ‘ALL’ instead of IP address/Net-mask value

Add Firewall Rule

firewall-cmd --permanent --add-service=snmp#firewall-cmd --permanent --add-service=http# firewall-cmd --reload

Change permissions to allow web browsing

chown -R apache: /var/www/html/
systemctl restart httpd

Schedule data collection using crontab

crontab -e
/5   * env LANG=C LC_ALL=C /usr/bin/mrtg /etc/mrtg/router.cfg --lock-file /var/lock/mrtg/mrtg_a --confcache-file /var/lib/mrtg/mrtg.ok

Conclusion: If you would like to configure multiple routers/Devices to monitor via this tool generate multiple configuration files using device names as config file names

Configuration file

cat /etc/mrtg/router.cfg

# Created by
# /bin/cfgmaker --snmp-options=:::::2 --ifref=descr ifdesc=descr ArkIT@192.168.2.5


### Global Config Options

# for UNIX
WorkDir: /var/www/html/

# or for NT
# WorkDir: c:\mrtgdata

### Global Defaults

# to get bits instead of bytes and graphs growing to the right
Options[_]: growright, bits

EnableIPv6: no

######################################################################
# System: rhel7
# Description: Linux rhel7 3.10.0-693.21.1.el7.x86_64 #1 SMP Wed Mar 7 19:03:37 UTC 2018 x86_64
# Contact: root@localhost
# Location: Unknown
######################################################################


### Interface 2 >> Descr: 'ens192' | Name: 'ens192' | Ip: '192.168.2.5' | Eth: '00-50-56-82-d9-83' ###

Target[192.168.2.5_ens192]: \ens192:ArkIT@192.168.2.5:::::2
SetEnv[192.168.2.5_ens192]: MRTG_INT_IP="192.168.2.5" MRTG_INT_DESCR="ens192"
MaxBytes[192.168.2.5_ens192]: 1250000000
Title[192.168.2.5_ens192]: Traffic Analysis for ens192 -- rhel7
PageTop[192.168.2.5_ens192]: <h1>Traffic Analysis for ens192 -- rhel7</h1>
<div id="sysdetails">
<table>
<tr>
<td>System:</td>
<td>rhel7 in Unknown</td>
</tr>
<tr>
<td>Maintainer:</td>
<td>root@localhost</td>
</tr>
<tr>
<td>Description:</td>
<td>ens192 </td>
</tr>
<tr>
<td>ifType:</td>
<td>ethernetCsmacd (6)</td>
</tr>
<tr>
<td>ifName:</td>
<td>ens192</td>
</tr>
<tr>
<td>Max Speed:</td>
<td>1250.0 MBytes/s</td>
</tr>
<tr>
<td>Ip:</td>
<td>192.168.2.5 (rhel7)</td>
</tr>
</table>
</div>