Configuring LibreNMS

Goals

 

Introduction

In this exercise, we will set up LibreNMS as our network monitoring package.

Setting the SNMP community

First, let's change the SNMP community that LibreNMS will try when discovering and adding new devices.

First, if you not already root, you should do:

$ sudo bash

Next, edit the file /opt/librenms/config.php,

# editor /opt/librenms/config.php

and find the line:

$config['snmp']['community'] = array("public");

And change it to:

$config['snmp']['community'] = array("NetManage");

 

Tell LibreNMS which subnets it's allowed to scan automatically

By default, LibreNMS will try ask for the list of “neighbors” that network devices "see" on the network. This is done using the Link Layer Discovery Protocol (LLDP) or Cisco's CDP (Cisco Discovery Protocol).

But to be on the safe side, and not scan networks outside your organization, LibreNMS needs to be told which subnets it's allowed to scan for new devices.

Still in the file /opt/librenms/config.php, find the line:

#$config['nets'][] = "10.0.0.0/8";

And replace this with the following to scan our specific subnets in use by our network and the workshop infrastructure.

$config['nets'][] = "10.10.0.0/16";

We need to make one more change...

 

Tell LibreNMS not to add duplicate devices

A situation can happen where two devices have duplicate SNMP sysName. (that's hostname in IOS) They could be two different devices, so it would be a good idea to have LibreNMS automatically add and monitor them.

But it can also happen that the SAME device is seen multiple times by LibreNMS - once using LLDP/CDP, and another time via OSPF (for example).

In that case, it ends up added twice. For instance, you may suddenly see two devices called rtr2-fa0-0.ws.nsrc.org and rtr2, and this is not what we want.

Since "both" devices are in fact the same, their SNMP sysName will be identical, and we can tell LibreNMS to NOT add devices if one already exists with the same sysName - after all, this shouldn't happen in a well configured network! :)

Here's an example of this:

2016-07-06 20:16:47 rtr4 discovery Device rtr4 (10.10.0.224) (port FastEthernet0/0) autodiscovered through CDP on rtr1.ws.nsrc.org
2016-07-06 20:09:45 rtr4-fa0-0 discovery Device rtr4-fa0-0.ws.nsrc.org (10.10.0.224) (port ) autodiscovered through OSPF on rtr1-fa0-0.ws.nsrc.org

To avoid this, add the following line at the bottom of the config.php file:

$config['allow_duplicate_sysName'] = false;

... this will prevent LibreNMS from adding the device if it exists already with the same sysName. You will be able to see if there are duplicate devices deteced in the Event Log (Overview -> Event Log).

After you've added the above setting, save the file and exit - we’re nearly done!

 

Add a host

Let's add localhost (i.e.: YOUR virtual server), using the following commands. Later you'll do this from the Web interface:

# cd /opt/librenms
# php addhost.php localhost NetManage v2c

You should see:

Added device localhost (1)

Notice we explicitly tell LibreNMS which SNMP community to use. We also assume it's SNMP v2c. If you're using v3, there are additional steps which aren't provided here.

Final Configuration

Discover and Poll newly added hosts

LibreNMS first “discovers” each host that has been added. This means that it methodically examines each host you added and figures out what it should monitor. The discover.php script does not automatically scan your network to find new devices. To run this script do:

# cd /opt/librenms
# sudo -u librenms php discovery.php -h all

NOTE: This could take some time. If you try to add devices that do not yet have an snmp service configured, then the discovery script takes a while to time out.

Once this has finished you can now "poll" the hosts. This means LibreNMS now knows what it wishes to monitor for each host, but it has yet to populate its database with initial values for each item. To do this we do:

# sudo -u librenms php poller.php -h all

As you can see the poller.php script does quite a bit with just a few devices. When we add it to a cronjob below this helps explain why LibreNMS is a resource intensive tool.

Create cronjob

Create the cronjob which will run periodic tasks required by LibreNMS:

# cd /opt/librenms
# cp librenms.nonroot.cron /etc/cron.d/librenms

One last thing: edit the file /etc/cron.d/librenms ...

# editor /etc/cron.d/librenms

...and find the line:

*/5  * * * *  librenms  /opt/librenms/cronic /opt/librenms/poller-wrapper.py 16

And change the ''16'' at the end to ''4'' (we have a single processor, and 4 threads is plenty)

*/5  * * * *  librenms  /opt/librenms/cronic /opt/librenms/poller-wrapper.py 4

Save, and exit.

 

Install complete

That's it! You now should be able to log in to http://librenmsN.ws.nsrc.org/ and begin to explore the information being collected for your monitored devices.

You can add some additional devices via the LibreNMS web interface. Why not add:

using the class snmp community. See if you can figure out how to do this on your own.

PLEASE NOTE: We have not covered HTTPS setup in this example, so your LibreNMS install is not secure by default. Please do not expose it to the public Internet unless you have configured HTTPS and taken appropriate web server hardening steps.

About Daily Updates

LibreNMS performs daily updates by default. At 00:15 system time every day, a git pull --no-edit --quiet is performed. If you don't want this, change the default by editing your ''config.php'' file. Remove the comment (the ''#'' mark) on the line:

#$config['update'] = 0;

so that it looks like this:

$config['update'] = 0;