Currently viewing the category: "netfilter"

How to Build and Use libnetfilter_queue for Android

By On December 1, 2011 · 2 Comments

If you’re looking for general information about how to use libnetfilter_queue for Linux, please refer here.

0. Preparation
First, you’ll need to check if your Android system kernel is compiled with support for libentfilter_queue. Follow the following steps,

Connect your android device to your computer. Enter command “adb pull /proc/config.gz” to get the config.gz [...]

Continue Reading →

How to Configure, Install and Use libnefilter_queue on Linux

By On December 1, 2011 · 8 Comments

According to libnetfilter_queue home page, libnetfilter_queue is a userspace library that allows one to retrieve and manipulate the packets that have been queued by kernel packet filter. It is supposed to replace the old ip_queue/libipq mechanism.
0. Dependencies
libnetfilter_queue requires a kernel that includes nfnetlink_queue subsystem. If you Linux kernel is 2.6.14 or later, [...]

Continue Reading →

How to Calculate IP/TCP/UDP Checksum–Part 3 Usage Example and Validation

By On November 27, 2011 · 2 Comments

This is a follow up of the previous post IP/TCP/UDP Checksum Calculation part 1 theory, and part 2 implementation.

This post gives an example using libnetfiler_queue library and the checksum code we implemented in part 2 to illustrate how to use the checksum code and verify that our code [...]

Continue Reading →

How to Write a Linux Firewall in Less than 1000 Lines of Code–Put Everything Together

By On July 31, 2011 · 4 Comments

This is the final post of how to write a Linux firewall in less than 1000 lines of code. If you haven’t read previous posts, you may want to do so in order to understand this post.

Part 1: Overview

Part 2: Command Line Arguments Parsing in glibc

[...]

Continue Reading →

How to Write a Linux Firewall in Less than 1000 Lines of Code Part 1–Overview

By On July 23, 2011 · 8 Comments

Side note: This article is based on a project in my master course about computer system security at 2010. I’m writing this article to recall the knowledge I’ve learned through the project and also hoping someone else can benefit from it.

Features of the Firewall

The firewall can BLOCK or UNBLOCK packets according to a [...]

Continue Reading →

How to Filter Network Packets using Netfilter–Part 2 Implement the Hook Function

By On July 23, 2011 · 4 Comments

This is a follow up of the previous blog: How to Filter Network Packets using Netfilter – Part 1 Netfilter Hooks. You should read the previous blog first in order to follow this tutorial.

The Hook Function Prototype

Once a hook function has registered with any of the 5 netfilter hooks, it’ [...]

Continue Reading →

How to Filter Network Packets using Netfilter–Part 1 Netfilter Hooks

By On July 22, 2011 · 3 Comments

Netfilter is a set of hooks inside Linux kernel. It allows kernel modules to register callback functions with the network stack in order to intercept and manipulate the network packet.

The Netfilter Hooks

The IPv4 packet traversal through Netfilter system can be illustrated as below,

Figure 1. Netfilter System hook

[...]

Continue Reading →
Set your Twitter account name in your settings to use the TwitterBar Section.