How to turn your CentOS box into a BGP router using Quagga

In a previous tutorial, I described how we can easily turn a Linux box into a fully-fledged OPSF router using Quagga, an open source routing software suite. In this tutorial, I will focus on converting a Linux box into a BGP router, again using Quagga, and demonstrate how to set up BGP peering with other […]
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How to turn your CentOS box into an OSPF router using Quagga

Quagga is an open source routing software suite that can be used to turn your Linux box into a fully-fledged router that supports major routing protocols like RIP, OSPF, BGP or ISIS router. It has full provisions for IPv4 and IPv6, and supports route/prefix filtering. Quagga can be a life saver in case your production […]
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How to use logrotate to manage log files in Linux

Log files contain useful information about what is going on within the system. They are often inspected during troubleshooting processes or server performance analysis. For a busy server, log files may grow quickly into very large sizes. This becomes a problem as the server will soon run out of space. Besides, working with a single […]
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How to monitor server memory usage with Nagios Remote Plugin Executor (NRPE)

In a previous tutorial, we have seen how we can set up Nagios Remote Plugin Executor (NRPE) in an existing Nagios setup. However, the scripts and plugins needed to monitor memory usage do not come with stock Nagios. In this tutorial, we will see how we can configure NRPE to monitor RAM usage of a […]
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How to create a site-to-site IPsec VPN tunnel using Openswan in Linux

A virtual private network (VPN) tunnel is used to securely interconnect two physically separate networks through a tunnel over the Internet. Tunneling is needed when the separate networks are private LAN subnets with globally non-routable private IP addresses, which are not reachable to each other via traditional routing over the Internet. For example, VPN tunnels […]
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What are useful CLI tools for Linux system admins

System administrators (sysadmins) are responsible for day-to-day operations of production systems and services. One of the critical roles of sysadmins is to ensure that operational services are available round the clock. For that, they have to carefully plan backup policies, disaster management strategies, scheduled maintenance, security audits, etc. Like every other discipline, sysadmins have their […]
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How to analyze Squid logs with SARG log analyzer on CentOS

In a previous tutorial, we show how to configure a transparent proxy with Squid on CentOS. Squid provides many useful features, but analyzing a raw Squid log file is not straightfoward. For example, how could you analyze the time stamps and the number of hits in the following Squid log? 1404788984.429 1162 172.17.1.23 TCP_MISS/302 436 […]
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How to set up Squid as a transparent web proxy on CentOS or RHEL

In a previous tutorial, we have seen the method of creating a gateway using iptables. This tutorial will focus on turning the gateway into a transparent proxy server. A proxy is called “transparent” when clients are not aware that their requests are processed through the proxy. There are several benefits of using a transparent proxy. […]
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How to set up a secure FTP service with vsftpd on Linux

FTP or File Transfer Protocol is one of the widely used services on the Internet, mainly for transferring files from one host to other. FTP itself was not designed as a secure protocol, and as such, the classic FTP service is vulnerable to common attacks such as man in the middle and brute force attacks. […]
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How to manage ip addresses and subnets with phpIPAM

A typical network/system admin is responsible for managing one or more subnets within the network under control. For example, when a LAN segment is assigned a /24 subnet, a total of 254 IP addresses can be used for different purposes. To keep track of what IP addresses are assigned to which hosts, some sort of […]
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