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Gentoo

Tunneling the hard way: using slirp, pppd and socat

Post date: January 29, 2006, 13:01 Category: Network Views: 12663 Comments
Tutorial quote: Every now and then you might come across a "bad" ISP. The one I have at home for example is dropping UDP packets ever so often when I try to play online games -- and it tends to drop random packets while I try to log onto a gameserver too which makes a certain game I like to play crash during the loading phase so it can't recover. I also heard of other ISPs blocking certain ports on external servers -- universities for example seem to like blocking p2p network ports and the school i was attending till last august blocked everything but port 80 for http -- including ftp which made even on-topic "research" a pita at times.
Usually there's three ways of working around this problem if "giving up" is not an option to you: a) change your ISP, b) use ssh to redirect ports, c) connect to an external VPN to route for you. a) can be tricky -- it's impossible if you're sharing the link with your parents and they insist on their email addresses or in the university/workplace/school scenario. b) will only work with single port/host combinations and for c) you will need a full-fledged rootbox idling around on the internet -- which tend to be expensive and "virtual servers" might not work because those often don't include tun/tap devices and/or kernel-level ppp support if you rent them and in case you rented them you probably can't fiddle around with its kernel to enable it (that was my problem at least). If any of this rings a bell to you, read on and discover method d)
Linux

Creating Really Teensy ELF Executables for Linux

Post date: April 12, 2005, 18:04 Category: Miscellaneous Views: 3221 Comments
Tutorial quote: If you're a programmer who's become fed up with software bloat, then may you find herein the perfect antidote.

This document explores methods for squeezing excess bytes out of simple programs. (Of course, the more practical purpose of this document is to describe a few of the inner workings of the ELF file format and the Linux operating system. But hopefully you can also learn something about how to make really teensy ELF executables in the process.)

Please note that the information and examples given here are, for the most part, specific to ELF executables on a Linux platform running under an Intel-386 architecture. I imagine that a good bit of the information is applicable to other ELF-based Unices, but my experiences with such are too limited for me to say with certainty.

The assembly code that appears in this document is written for use with Nasm. (Besides being more appropriate for our needs, Nasm's syntax beats the hell out of AT&T syntax for anyone who learned x86 assembly language before learning to use Gas.) Nasm is freely available and extremely portable; see http://nasm.sourceforge.net/.

Please also note that if you aren't a little bit familiar with assembly code, you may find parts of this document sort of hard to follow.
Linux

Rip DVDs in Linux the (Semi-)Easy Way

Post date: December 8, 2007, 14:12 Category: Multimedia Views: 4011 Comments
Tutorial quote: With its hacker-friendly aesthetic and open source mentality, you'd think a Linux desktop would be the best place to assert your digital rights—you know, make backup copies of your DVDs, convert them for iPods, that kind of thing.

And you'd be half right. There are plenty of programs that let you take control of your video discs, but they're only useful if you can make it through a maze of configuration menus, command line options, choices about bit rates and codecs, and the occasional confusing message about a missing library.

I've tried out a good number of DVD ripping and conversion programs, and I've made peace with one method, and one program, that gets the job done more often than not. It's not exactly one-click, but once your system is set up, you can drop in DVDs and back them up or convert them with relative ease.

Note on system differences: I set up my ripping/burning system on a Lenovo Thinkpad T61 running a brand-new installation of Ubuntu 7.10 (Gutsy Gibbon). As with so many things Linux, packages and commands may vary based on your system. But for the most part, the tools I use in this walkthrough work across distributions and on both major desktop environments, GNOME and KDE.
Linux

Three tools to help you configure iptables

Post date: May 25, 2005, 14:05 Category: Network Views: 3571 Comments
Tutorial quote: Every user whose client connects to the Internet should configure his firewall immediately after installation. Some Linux distributions include firewall configuration as a part of installation, often offering a set of defaults configurations to choose from. However, to ensure that your machine presents the minimum "attack surface" (a measure of the number of vulnerable ports, user accounts, and sockets exposed to attack) to the predatory inhabitants of the Internet, you may need to do some manual configuration of your firewall. Here are three tools that can help.
The Linux kernel (version 2.4 onwards) contains a framework for packet filtering and firewalling using netfilter and iptables. Netfilter is a set of hooks inside the Linux kernel that allows kernel modules to register callback functions with the network stack. Iptables is a generic table structure for the definition of rulesets. Each rule within an IP table consists of a number of classifiers (iptables matches) and one connected action (iptables target). Iptables has extensive documentation that can be accessed online or by typing man iptables at the command line. Yet despite the depth of the documentation available for iptables, its complexity can be baffling.
Linux

Linux Web Filtering in 7 steps

Post date: April 12, 2005, 18:04 Category: Network Views: 4587 Comments
Tutorial quote: How to install a transparent Squid proxy server with real-time HTTP virus scanning on Mandrake 10.0 using DansGuardian and ClamAV?

People quickly and easily access volumes of research on the Internet and correspond with a mouse click. For more and more companies, content filtering is part of the large battle to combat all kinds of online threats, including hackers, worms and viruses. Linux content filtering allows administrators to configure and manage Internet access across the entire network and to block unwanted Web content like pornography, shopping Web sites, games and gambling.

This guide contains all the necessary information for installing and understanding the architectural layout of the implementation. It was written with the assumption that you understand how to install programs and have a basic understanding of Linux Mandrake. This includes installing Linux Mandrake and RPM packages, editing files, making directories, compiling software and understanding general UNIX commands. This guide doesn’t explain how to use or configure Squid, DansGuardian and ClamAV but information on where to obtain this information can be found in the “Additional information” section.
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