Install SNMP on UBUNTU Linux

1. SNMPD

SNMPD is the service running SNMP on a managed entity. SNMP comes in 3 versions. Version 1, the one we are going to use here is not secured, therefore we are going to make sure that only localhost is going to be able to access it.
People opening the service to the outside should make sure that trusted hosts can access the service either though the use of iptables or through the use of /etc/hosts.allow.

1.1. Installing the SNMP server

The only package which is required on the server site is snmpd, the SNMP daemon.

To install it type:

$ sudo apt-get install snmpd

snmpd is now installed but we still have to tweak it a little bit to make it work as we want.

1.2. Configuring SNMPD

The first thing we want to make sure is that snmpd is only going to wait for connections on localhost. To do this, edit file /etc/default/snmpd and make sure those values are set:

SNMPDRUN=yes
SNMPDOPTS='-Lsd -Lf /dev/null -u snmp -I -smux -p /var/run/snmpd.pid 127.0.0.1'

If you want your server to listen on all interfaces, remove the 127.0.0.1 bit.

This setting will make sure that the service will be started and that the service is going to bind to localhost.

Finally, we are going to configure snmpd in such a way that it will only return datas to trusted host for a specific community.

Edit /etc/snmp/snmpd.conf and make sure that com2sec it only set to:

com2sec readonly localhost mycommunity

If you want a remote machine to be able to gather information for the community mycommunity, make sure you replace localhost by mynetwork, where mynetwork can be of the form: 1.1.1.1 or 1.1.0.0/16.

1.3. Checking SNMP configuration:

We are going to use the snmpwalk utility to verify that the server is working as wanted.

Here we want snmp to reply only to localhost for the community mycommunity.

From localhost

$ snmpwalk -Os -c mycommunity -v 1 localhost system

Should return a lot of output and:

snmpwalk -Os -c public -v 1 localhost system
Timeout: No Response from localhost

External Links......

http://www.net-snmp.com/

SNMP & MRTG

How 2 Configure SNMP and MRTG

SNMP server configuration

Firstly, you need an SNMP server to provide network interface statstics on demand:

# apt-get install snmpd

You need to edit the configuration for this as it does not allow any connections by default. With your favourite editor, edit:

/etc/snmp/snmpd.conf

Comment out the following (prefix with #):

com2sec paranoid default public

Insert the following underneath the commented out section:

com2sec readonly default public

That gives anyone with access to the SNMP server read-only access to the public community. This is the one that contains the interface statistics.

To apply the changes, restart snmpd:

/etc/init.d/snmpd restart

Make sure you firewall off any SNMP related ports so that you don't get any unwanted visitors (check netstat and /etc/services for port information).

Installation of MRTG

MRTG is the main collection and graphing component of the traffic monitoring solution I am presenting here. Firstly, install MRTG:

# apt-get install mrtg

You can manually or automatically generate the configuration file for mrtg. I would recommend doing it automatically as it is a lot easier. Issue the following command:

# cfgmaker --global 'WorkDir: /var/www/mrtg' \
   --output /etc/mrtg.cfg public@127.0.0.1

This will generate the configuration file. You then need to make an index file which contains a list of all of your interfaces. Issue the following command:

# indexmaker /etc/mrtg.cfg --columns=1 \
   --output /var/www/mrtg/index.html

You will now need to execute mrtg manually 3 times to create the required database files. Issue the following command 3 times sequentially. On the third run, you should see no errors being reported:

# mrtg

This is executed every 5 minutes by cron. The cron job was added by dpkg for you so you do not have to configure it.

Conclusion

Finally, inspect your results! You will not see any reasonable graphs for quite some time so sit back end relax for a bit!

Browse to http://your-server-name/mrtg/