Linux - SecurityThis forum is for all security related questions.
Questions, tips, system compromises, firewalls, etc. are all included here.
Welcome to LinuxQuestions.org, a friendly and active Linux Community.
You are currently viewing LQ as a guest. By joining our community you will have the ability to post topics, receive our newsletter, use the advanced search, subscribe to threads and access many other special features. Registration is quick, simple and absolutely free. Join our community today!
Note that registered members see fewer ads, and ContentLink is completely disabled once you log in.
If you have any problems with the registration process or your account login, please contact us. If you need to reset your password, click here.
Having a problem logging in? Please visit this page to clear all LQ-related cookies.
Introduction to Linux - A Hands on Guide
This guide was created as an overview of the Linux Operating System, geared toward new users as an exploration tour and getting started guide, with exercises at the end of each chapter.
For more advanced trainees it can be a desktop reference, and a collection of the base knowledge needed to proceed with system and network administration. This book contains many real life examples derived from the author's experience as a Linux system and network administrator, trainer and consultant. They hope these examples will help you to get a better understanding of the Linux system and that you feel encouraged to try out things on your own.
Click Here to receive this Complete Guide absolutely free.
This is my first try configuring a linux box to serve as an internet server for about 75 PCs in our office. I am using a Red Hat Linux 9 distribution with kernel 2.4.20-8, and iptables ver. 1.2.7a. I need to create a customized iptables script to allow our private network to access the internet using NAT or masquerading since we have only one official IP address assigned. The built-in iptables file in the directory /etc/sysconfig/iptables cannot be customized. It can only be modified with its features using the "lokkit" utility for allowing incoming packets such as HTTP and Mail but it has no feature for doing NAT or MASQUERADING. I tried manually editing the /etc/sysconfig/iptables file and did a /etc/init.d/iptables restart but it did not work. It only issued a "Bad argument 'iptables'" error and a "Try 'iptables-restore' and a [FAILED] message instead of [OK] it if started normal. How do I go about this? I replaced the built-in iptables file with the one I created but it also does not work. Please advise.
The /etc/sysconfig/iptables file shouldn't ever be directly modified. It's extremely sensitive to syntax and certain rules will not work even if the syntax is 100% correct. Instead enter the iptables rules on the command line, verify that everything works to your liking, then do service iptables save. That will modify the iptables file for you.
FWIW, you should just need to do something like this from the commandline (as root):
iptables -A POSTROUTING -o <external_interface> -j MASQUERADE
May or may not need these as well:
iptables -I FORWARD -i <external_interface> -o <internal_interface> -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -I FORWARD -i <internal_interface> -o <external_interface> -j ACCEPT
Also make sure that packet forwarding is on:
echo 1 > /proc/sys/net/ipv4/ip_forward