Nagios For Network Management

Nagios

What is Nagios

• “Nagios is an enterprise-class monitoring solutions for hosts, services, and networks released under an Open Source license.”
• It watches hosts and services that you specify, alerting you when things go bad and again when they get better.”
• Developed by Ethan Galstad
• Nagios is quite powerful and flexible, but unfortunately its not very friendly to newbies. 
• Why? Because it takes a lot of work to get it installed and configured properly. 
• That being said, if you stick with it and manage to get it up and running, you’ll never want to be without it.

Introduction

• Nagios: a measurement tool that actively monitors availability of devices and services: 
• Popular: One of the most used open source network monitoring software packages.
• Fast: Uses CGI functionality written in C for faster response and scalability.
• Scalable: Can support up to thousands of devices and services.
• Cool-Looking Web Interface®

Monitoring of…

• Nagios can supervise:

Hosts (Windows, Linux, …) 

• Monitoring of host resources (processor load, disk usage, system logs) on a majority of network operating systems, even Microsoft Windows 
•    Remote monitoring supported through SSH or SSL encrypted tunnels. 

monitoring of network services (SMTP, POP3, HTTP, NNTP, ICMP, SNMP) SNMP Traps
other hardware devices (like temperature sensors,filling level indicator,…)

• In case of emergency send notifications: email, pager, SMS

any user-defined method through plug-in system

What’s good about Nagios?

• It’s conceptually simple
• It handles the load
• It has a web interface
• It’s extensible
• It’s not overly noisy

“Cool-Looking Web Interface®”

Features: 1

• Modular
• Type of availability is largely delegated to plug-ins:

1.           The product's architecture is simple enough that writing new plugins is fairly easy in the language of your choice.
2. There are many, many, many plug-ins available.

Features: Plug-Ins or Modular

• The Nagios package in Ubuntu comes with a number of pre-installed plugins:

 ** apt.cfg    breeze.cfg    dhcp.cfg    disk-smb.cfg    disk.cfg dns.cfg    dummy.cfg    flexlm.cfg    fping.cfg    ftp.cfg   games.cfg    hppjd.cfg http.cfg   ifstatus.cfg   ldap.cfg   load.cfg    mail.cfg    mrtg.cfg mysql.cfg netware.cfg   news.cfg    nt.cfg    ntp.cfg    pgsql.cfg    ping.cfg     procs.cfg radius.cfg    real.cfg  rpc-nfs.cfg    snmp.cfg   ssh.cfg    tcp_udp.cfg telnet.cfg    users.cfg    vsz.cfg **

• There are many more available (e.g.)...

                      http://sourceforge.net/projects/nagiosplugins

Features: 2

• Fast and Scalable
• Compiled, binary CGIs and common plug-ins for faster performance.
• Parallel checking and forking of checks to support large numbers of devices.

1. This has been considerably improved in version 3 of Nagios.
2. Improvement of efficiency is a controversial topic in the Nagios community. 

Features: 3

• Uses “intelligent” checking capabilities.

               * Attempts to distribute the server load of running Nagios (for larger sites) and the load placed on devices being checked. 

• Configuration is done in simple, plain text files, that can contain much detail and are based on templates.
• Nagios reads it's configuration from an entire directory. You decide how to define individual files.

Features: 4

• Topology Aware: To determine dependencies.

 Differentiates between what is down vs. what is not available. This way it avoids running unnecessary checks. This is done using parent-child relationships between devices.

• Notifications: How they are sent is based on combinations of:

Contacts and lists of contacts.

Devices and groups of devices

Services and groups of services

Defined hours by persons or groups.

The state of a service.

Features: 5

• Service state:

• When configuring a service you have the following notification options:

1. d: DOWN: The service is down (not available)
2. u: UNREACHABLE: When the host is not visible
3. r: RECOVERY: (OK) Host is coming back up
4. f: FLAPPING: When a host first starts or stops or it's state is undetermined.
5. n: NONE: Don't send any notifications

How Checks Work

• Parameters: Set in /etc/nagios3/nagios.cfg:

1. Normal checking interval
2. Re-check interval
3. Maximum number of checks.
4. Period for each check

• Services check(s) only happen when a node responds (ping check or “is alive = yes”):

1. Remember a node can be:

              DOWN

              UNREACHABLE

The Concept of “Parents”

1. For example, the parent of a PC connected to the switch mgmt-sw1 would be mgmt-sw1.
2. This allows us to specify the network dependencies that exist between machines, switches, routers, etc.
3. This avoids having Nagios send alarms when a parent does not respond.
4. Note: A node can have multiple parents.

The Idea of Network Viewpoint

• Where you locate your Nagios server will determine your point of view of the network.
• Nagios allows for parallel Nagios boxes that run at other locations on a network.
• Often it makes sense to place your Nagios server nearer the border of your network vs. in the core, or...
• Have someone else run checks for you from an external location as well.

Network Viewpoint

By : mogtaba altyib 
Modification by : Mohammed Bakry PhD