Step # 1 : Make sure snmp server installed

# rpm -qa | grep snmp

# yum install net-snmp-utils net-snmp

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

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

# ps -aux | grep snmp

Output:

root   5512  0.0  2.3  5872 3012 pts/0    S    22:04   0:00 /usr/sbin/snmpd

Alternatively, you can try any of the following two commands as well:

# lsof -i :199

Output:

COMMAND  PID USER   FD   TYPE DEVICE SIZE NODE NAME
snmpd   5512 root    4u  IPv4  34432       TCP *:smux (LISTEN)

OR try out netstat command:

# netstat -natv | grep ':199'

Output:

tcp        0      0 0.0.0.0:199             0.0.0.0:*               LISTEN

If you found service is running or listing on port 199 then please see step #3; otherwise start service using following command:

# service snmpd start

Make sure snmpd service starts automatically, when linux comes us (add snmpd service):

# chkconfig --add snmpd

Step # 3 : Make sure snmp server configured properly

Run snmpwalk utility to request for tree of information about network entity. In simple words query snmp server for your IP address (assigned to eth0, eth1, lo etc):

# snmpwalk -v 1 -c public localhost IP-MIB::ipAdEntIfIndex


ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.0.3 = 2

If you can see your IP address then please proceed to step 4; else it is a time to configure snmp server as follows (by default RHEL and RH 8/9 are not configured for snmp server for security reason):

Configure SNMP

(1) Edit file /etc/snmp/snmpd.conf using text editor:

# vi /etc/snmp/snmpd.conf

Change/Modify line(s) as follows:

Find following Line:

com2sec notConfigUser  default       public

Replace with (make sure you replace 192.168.0.0/24 replace with your network IPs) following lines:

com2sec local     localhost           public
com2sec mynetwork 192.168.0.0/24      public

Scroll down bit and change:

Find Lines:

group   notConfigGroup v1           notConfigUser
group   notConfigGroup v2c           notConfigUser

Replace with:

group MyRWGroup v1         local
group MyRWGroup v2c        local
group MyRWGroup usm        local
group MyROGroup v1         mynetwork
group MyROGroup v2c        mynetwork
group MyROGroup usm        mynetwork

Again scroll down bit and locate following line:

Find line:

view    systemview     included      system

Replace with:

view all    included  .1                               80

Again scroll down bit and change:

Find line:

access  notConfigGroup ""      any       noauth    exact  systemview none none

Replace with:

access MyROGroup ""      any       noauth    exact  all    none   none
access MyRWGroup ""      any       noauth    exact  all    all    none

Scroll down bit and change:

Find lines:

syslocation Unknown (edit /etc/snmp/snmpd.conf)
syscontact Root  (configure /etc/snmp/snmp.local.conf)

Replace with (make sure you supply appropriate values):

syslocation Linux (RH3_UP2), Home Linux Router.
syscontact Vivek G Gite

For your convenient, here is my /etc/snmp/snmpd.conf file. Feel free to use this file. Make sure you make backup of your existing file if you use this file as it is.

Start your snmp server and test it:

(a) Make sure when linux comes up snmpd always starts:

 # chkconfig snmpd on

(b) Make sure service start whenever Linux comes up (after reboot):

 # service snmpd start

(c) Finally test your snmp server:

 # snmpwalk -v 1 -c public localhost IP-MIB::ipAdEntIfIndex

Step # 4 : Install mrtg if not installed

Mrtg software may install during initial installation; you can verify if MRTG installed or not with following RPM command:

rpm -qa | grep mrtg

If mrtg already installed please see step # 5; else use rpmfind.net to find MRTG rpm or up2date command to install MRTG software:

# up2date -v -i mrtg

Fedora Linux user can use yum command as follows to install MRTG:

# yum install mrtg

Step # 5 : Commands to Configure mrtg

(a) Create document root to store mrtg graphs/html pages:

# mkdir -p /var/www/html/mymrtg/

(b) Run any one of the following cfgmaker command to create mrtg configuration file:

# cfgmaker --global 'WorkDir: /var/www/html/mymrtg' --output /etc/mrtg/mymrtg.cfg public@localhost

OR (make sure your FQDN resolves, in following example i'm using rh9.test.com which is my router FQDN address)

# cfgmaker --global 'WorkDir: /var/www/html/mymrtg' --output /etc/mrtg/mymrtg1.cfg [email protected]

(c) Create default index page for your MRTG configuration:

# indexmaker --output=/var/www/html/mymrtg/index.html /etc/mrtg/mymrtg.cfg

注意：这一步可能会报如下的错误：

Use of uninitialized value $first in hash element at /usr/bin/indexmaker line 353.
这是因为上一步(cfgmaker那一步)生成的文件由于某种原因全被注释了，如

### Interface 1 >> Descr: 'lo' | Name: 'lo' | Ip: '127.0.0.1' | Eth: '' ###
### The following interface is commented out because:
### * it is a Software Loopback interface
.

.

### Interface 2 >> Descr: 'eth0' | Name: 'eth0' | Ip: '192.168.0.117' | Eth: '52-54-00-00-00-17' ###
### The following interface is commented out because:
### * has a speed of 0 which makes no sense
这时只要手动修改/etc/mrtg/mymrtg.cfg去注释并修改第二个接口的下面一行

MaxBytes[localhost_2]: 1250000
再运行以上命令就不会有问题

(d) Copy all tiny png files to your mrtg path:

# cp -av /var/www/mrtg/*.png /var/www/html/mymrtg/

Step # 6 First test run of mrtg

(a) Run mrtg command from command line with your configuration file:

# env LANG=C /usr/bin/mrtg /etc/mrtg/mymrtg.cfg
# /etc/init.d/httpd start

Note: You may get few warning message for first time; ignore them.and run it three time

(b) Fire your favorite web browser (like FireFox :D ) and type url http://www.your.com/mymrtg/ or http://your-ip/mymrtg/

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

(a) Login as a root user or login as a mrtg user and type following command:

# crontab -e

(b) Add mrtg cron job entry to configuration file (append following line to it):

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

Save file and you are done with MRTG config issues :)

Step # 8 Block ports 161 & 162 at firewall

You do not want to give access to everyone to your snmp server for security reasons. SNMP server uses UDP 161, 162 ports for communication. Use Linux IPTABLES firewall to restrict access to SNMP server

(a) Allow outgoing SNMP server request from your Linux computer. This is useful when you query remote host/router (replace SERVER IO with your real IP):

SERVER="xxx.xxx.xxx.xxx"
iptables -A OUTPUT -p udp -s $SERVER --sport 1024:65535 -d 0/0 --dport 161:162 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p udp -s 0/0 --sport 161:162 -d $SERVER --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT

(b )Allow incoming SNMP client request via iptables. This is useful when you wish to accept queries for rest of the world (replace SERVER IP with your real IP):

SERVER="xxx.xxx.xxx.xxx"
iptables -A INPUT -p udp -s 0/0 --sport 1024:65535 -d $SERVER --dport 161:162 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p udp -s $SERVER --sport 161:162 -d 0/0 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT

Pleae note that above two are just SNMP specific iptables rules. Please consult iptables(8) man page for complete information on iptables

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

Once again, you would like to restrict access to your MRTG reports. This can easily accomplished with Apache webserver's .htaccess file. If you are on webhosting server with control panel (such as ensim or plesk) then you can use control panel itself to create password-protected directory.

Below is process outlined to protect graphs using apache's .htaccess file and htpasswd command:

Step # 1: Create .htaccess file in /var/www/html/mymrtg/ directory (add text as follows):

vi /var/www/html/mymrtg/.htaccess

Add following text to file:

AuthName "MRTG Graphs/Html restricted access"
AuthType Basic
AuthUserFile /var/members/.htpasswd
require user mrtgadmin

Step # 2: Create a user and password name (-c assumes first time you are using .htpasswd file):

# htpasswd -c /var/members/.htpasswd mrtgadmin

For more information please see Apache Webserver Authentication and access control mini-howto.