Understanding Firewall configurations

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Understanding Firewall configurations

Install iptables package

Before starting, we must make sure that iptables RPM installed. The iptables RPM is there in RedHat Linux installation CD #2. The file name generally starts with software package name with its version name as this:

iptables-1.2.11-3.1.RHEL4.i386.rpm.

Starting iptables

We can start, stop, and restart iptables after booting the system using the following commands:

# service iptables start

# service iptables stop

# service iptables restart

Firewalls

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Firewalls:

Data direction in iptables: This command is based on controlling data traffic in three directions: IN, OUT and THORUGH. That is, we can configure our iptables to stop data from entering into our LAN from outside network, stop data from leaving our computer, and control the data that travels forward between LAN and the internet.

Chains in iptables: Most of the firewalls are based on series of iptables commands. These commands are connected as chains. The RedHat Linux saves firewall commands in /etc/sysconfig/iptables file.

Pluggable Authentication Modules (PAM)

These modules are used to limit access to specific application, as redhat-config-network or reboot, to the root user itself. Different PAM modules let us control access by password, by access location or by user.

Network security – firewalls and PAM

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Network security – firewalls and PAM

Firewalls

Computer firewalls are used to serve the same purpose as the physical firewalls, i.e. to keep fire from spreading. Here the fire is unwanted and unauthorized attackers. In networking world a firewall is also called as Packet filter. Firewall can either be a physical piece of hardware or it can be software that sits between our network and internet. It controls and regulates the flow of information.

Linux system acts as a filtering firewall. A filtering firewall filters traffic flowing between our network and the internet. It can limit the type of communication. It can also limit the access to or from the internet to specific computers on our network.

For Linux to work as filtering firewall, we either can use iptables or ipchains. The iptables is newer than ipchains, and is used as default firewall now a day. We can set different levels of firewalls for different systems on the network.

Network Trouble shooting:

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Network Troubleshooting:

1. Using ping command

For checking the communication between wireless nodes also, we can use ping command. If wireless LAN card drivers are properly installed and access point is powered on, but still we are receiving the message Network Unreachable, it means that we have network configuration problem. For this we can check the following:

• IP address: We should run ifconfig command to get the exact IP of the required computer.
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• Computer name: If the ping by computer name is failing, we must check that our computer is able to resolve the desired computer name properly. For this we can check /etc/hosts file and update it, if required so.
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2. Defining gateway address

If the wireless computers on LAN are able to access each other but they are not able to communicate with the computers out side of LAN, then we must check that the gateway address is configured properly or not.

3. Restart network service

We should always restart the network interface, after making some changes in it:

# service network restart

# service pcmcia restart