This article aims to familiarise you with IP addresses and subnets and the calculations involved when setting them up. It’s a big topic, so this article will try to stay focused on its practical side to help get you on the right track and subnetting… Read More »Calculating IP Addresses and Subnets – A Reference
When your computer acts as a server, such as a web server or a database server, that server process must listen on a port that other computers connect to. It’s useful to be able to find out what ports are open on your Linux server should… Read More »How to Easily Check if a Network Port is Open in Linux
The ifconfig command is obsolete, and you should no longer use it! This tutorial covers the ip command, which you should use in place of ifconfig. Here’s how to use the ip command instead. The ip command can do a bunch of other stuff as well, but we’ll focus… Read More »STOP Using the Linux ifconfig Command [Here’s Why]
SCP or Secure Copy securely transfers files between two hosts over the network using the SSH protocol. This tutorial explains how to use this popular command with numerous examples. SCP is pre-installed with most Linux distributions and is often used for deploying software to servers and backing up – frequently… Read More »Using the SCP Command to Securely Copy Files [Examples]
This guide explores the 500 internal server error code, an HTTP error, and how to fix it. HTTP Errors and Error Codes Whenever a web page is loaded, a request is made to an HTTP server (Most web servers run Linux, by the way), and… Read More »What Is a 500 Internal Server Error and How to Fix It?
dig is the Linux command-line tool used to look up the DNS records for a host. This tutorial explains how to use this command and includes handy examples. DNS records provide information to your computer about a host’s IP address on a network, email configuration, or… Read More »How to Use the Dig Command [With Examples]
Few will deny that monitoring of Cisco devices is essential part of sysadmin’s job. I personally use Nagios to track states of BGP neighbors on Cisco routers so if one of peers goes down I’ll receive a phone call from Nagios. You may have redundant… Read More »Track Cisco BGP peers using Nagios
Nfsen is open source sensor: it accepts netflow data from multiple netflow probes (servers, routers, vpn concentrators etc) and then visualizes it into human readable form. So using Nfsen you can see traffic statistics of every network device in your network in one place (actually Nfsen provides much more features).
By default Nfsen makes it possible to see only inbound and outbound traffic statistics but no protocol breakdown or any traffic classification. In the meantime it’s always useful to know what network applications are eating the bandwidth to understand if that fits baseline or not and take necessary actions. For example, if you’re monitoring Linux server which primary task is to host some website but in Nfsen you see that it generates 90% of SSH traffic and only 10% of web traffic then it would be reasonable idea to check if somebody is trying to brute force SSH password and stop that activity. In other words it’s better to have traffic statistics classified. In this article I’ll tell you how to enable traffic classification in Nfsen.
The Implementing Cisco IP Routing (CCNP Route 642-902). Materials for efficient preparation to the exam.
A few days ago I have successfully passed 642-902 exam (CCNP ROUTE v6) and would like to share the list of materials I have been using to prepare to that exam. To get prepared I was using official Cisco Press training resourses, lab simulations and… Read More »The Implementing Cisco IP Routing (CCNP Route 642-902). Materials for efficient preparation to the exam.
There is Cisco router of 7200 series with 4 FastEthernet interfaces (FE) and 2 serial ports. It should act as load balancer and failover for LAN connected to it via one FE 1/0 interface while two identical Internet connections are going to FE 0/0 and… Read More »Cisco Load Balancing with Failover setup example