Network Management & Monitoring with Linux
In today's world, where all the computing revolves around the concept of networking, the work for system administrators has become more and more overwhelming. It is the mission of maintaining the availability of resources such as routers, hubs, servers and every critical device in the network.
There are many reasons managers would like to monitor network devices: bandwidth utilization, operational state of links, bottlenecks, problems with the cabling or routing information distributed between its devices, etc. Monitoring network activity is also a good starting point for discovering security problems and misbehaviors.
In many cases, the network of an organization includes expensive links to remote networks (WAN) or the Internet, whose costs may be based on traffic volume. It's very important to maintain statistics of traffic going through these links. This is a very common task in Europe, where X.25 links are still very common. These links are charged on the basis of packets transmitted and received.
Other types of links, like Point to Point or Frame Relay, are usually charged on a flat rate. In these, the telco ensures a bandwidth that is important to monitor.
In the final part of this article we focus on a tool designed to monitor traffic in router interfaces, with a great graphical representation of this information. It can be easily modified to monitor other kinds of information.
The answer to all these needs is a protocol named Simple Network Management Protocol (SNMP). Designed in the '80s, SNMP's initial aim was to integrate the management of different types of networks with a simple design that caused very little stress on the network.
SNMP operates at the application level using TCP/IP transport-level protocols so it can ignore the underlying network hardware. This means the management software uses IP, and so can control devices on any connected network—not just those attached to its physical network. This also has disadvantages: if the IP routing is not working correctly between two devices, it's impossible to reach the target to monitor or reconfigure it.
There are two main elements in the SNMP architecture: the agent and the manager. It's a client-server architecture, where the agent is the server and the manager is the client.
The agent is a program running in each of the monitored or managed nodes of the network. It provides an interface to all the items of their configuration. These items are stored in a data structure called a management information base (MIB), which we explain later. It's the server side, as long as it maintains the information being managed and waits for commands from the client.
The manager is the software that runs in the monitoring station of the network, and its role is contacting the different agents running in the network to poll for values of its internal data. It's the client side of the communication.
There is a special command in the SNMP command set called trap that permits an agent to send unsolicited data to the manager, to inform it of events, such as errors, shutdowns, etc.
In essence, SNMP is a very simple protocol as long as all the operations it performs deal with the fetch-and-store paradigm, and this allows for a small commands set. A manager can perform only two different operations on an agent: request or set the value of a variable in the MIB of the agent. These two operations are known as get-request and set-request. There's a command to respond to a get-request called get-response, which is used only by the agent.
The extensibility of the protocol is directly related to the capability of the MIB to store new items. If a manufacturer wants to add some new commands to a device such as a router, he must add the appropriate variables to its database (MIB).
Almost all manufacturers implement versions of SNMP agents in their devices—routers, hubs, operating systems, and so on. Linux is not an exception to this, and publicly available SNMP agents for Linux can be found on the Internet.
SNMP provides very little support for authentication schemes. It supports only a two-password scheme. The public allows managers to request the values of variables, and the private allows these values to be set. These passwords in SNMP are called communities. Every device connected to an SNMP-managed network must have these two communities configured. It is very common to have the public community set to “public” and the private community to “private”, but it's very important to change these values to reflect the security policy of your organization.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide