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 Internet connection sharing with iptables on Linux

In this tutorial, I’ll explain how to share a single Internet connection among multiple devices on Linux. While consumer-grade WiFi routers have become mainstream nowadays, making this problem a non-issue, suppose you don’t have one at home. However, say you have a Linux box already assembled with a modem and a LAN card. The modem […]
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How to close an open DNS resolver

The DNS server that we have created in the previous tutorial is an open DNS resolver. An open resolver does not filter any incoming requests, and accepts queries from any source IP address. Unfortunately, an open resolver can become an easy target to attackers. For example, attackers can initiate a Denial of Service (DoS) or […]
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How to set up a transparent HTTPS filtering proxy on CentOS

HTTPS protocol is used more and more in today‚Äôs web. While this may be good for privacy, it leaves modern network administrator without any means to prevent questionable or adult contents from entering his/her network. Previously it was assumed that this problem does not have a decent solution. Our how-to guide will try to prove […]
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How to configure firewall via command line on Linux

If you are looking to configure firewall on Linux, consider CSF (ConfigServer Security & Firewall). CSF is an easy-to-use, yet versatile firewall configuration tool written in Perl. Using CSF, you can easily configure advanced firewall rules such as stateful packet inspection and intrusion detection filters via its command-line interface or CSF configuration file. CSF is […]
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What are available iptables management tools with GUI?

Netfilter is a packet filtering system within the Linux kernel used for intercepting and processing network packets. Iptables is a user-space program that relies on netfilter to implement stateless/stateful packet filtering for network firewalls, and address/port translation for NATs. There are many applications and tools that ease complex iptables management tasks with convenient graphical front-ends. […]
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How to run iptables automatically after reboot on Debian

If you have customized iptables rules, and would like to load the customized iptables rules persistently across reboots on Debian, you can leverage if-up.d scripts that are located in /etc/network/if-up.d. On Debian, any script that is marked as executable and placed in /etc/network/if-up.d gets executed when a network interface is brought up. In order to […]
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