Ipcalc is a simple tool to calculate network, broadcast, netmask, etc. from an IP address.

It also gives the class of the IP. It might facilitate the work of network admins.

Here is an example of using it against a “local” IP address:

Example 1:

Deb:~# ipcalc 192.168.4.25
Address: 192.168.4.25 11000000.10101000.00000100. 00011001
Netmask: 255.255.255.0 = 24 11111111.11111111.11111111. 00000000
Wildcard: 0.0.0.255 00000000.00000000.00000000. 11111111
=>
Network: 192.168.4.0/24 11000000.10101000.00000100. 00000000
HostMin: 192.168.4.1 11000000.10101000.00000100. 00000001
HostMax: 192.168.4.254 11000000.10101000.00000100. 11111110
Broadcast: 192.168.4.255 11000000.10101000.00000100. 11111111
Hosts/Net: 254 Class C, Private Internet

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Linux machines are known to be pretty secure.

Studies have shown that Linux has been designed in a secure manner. Yet, despite all the security features that come bundled with a Linux installation, you need to configure these features correctly to make them work for you. I’ll guide you through the process of setting up of one of the tools that help secure your machine – the firewall. We will use the iptables firewall for this exercise. I am assuming that you are using a server running Red Hat Enterprise Linux 4 or similar. However, most of the steps should work fine on other Linux distributions as well. In this article we will setup a firewall on a Linux server running the Apache Web Server, FTP, and SSH.

Let us first see what ports these applications use and which of them need to have a port open on the firewall.

The Apache web server runs on port 80 by default. Apache is going to server all our web content on this port, therefore we need to keep this port open on the firewall. The SSH service runs on port 22. We need to be able to remotely connect to our server to work, so we keep it open. FTP runs on port 21 and it too needs the port to be open to communication.

Next, make sure you have iptables installed. Run this command as the root user:

apt-cache search iptables Continue Reading…

Step 1. Open the network configuration file (pico /etc/network/interfaces)

Check the name of your network interface. You should see a line similar to this one: “iface eth0 inet static”. In my case the name is eth0.

Add these lines to the end of the file:

auto eth0:1

iface eth0:1 inet static

address 192.168.1.3

netmask 255.255.255.0

broadcast 192.168.1.255

network 192.168.1.0

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You probably heard before of the term Denial of Service. What does this mean? How can you stop DOS?

Taking advantage of a known problem with the Operating System or any running services on the target, a good programmer can build an application that sends some data that causes the targeted system to crash.

The worst case scenario is not when a hacker crashes a service, but when it finds a way to maximize the CPU usage causing a total malfunction on the system.

Of course most of the attacks are not initiated by these kind of programmers, but by “script kiddies” who only read about it, find the program’s source over the web and just use it without knowing the mechanisms it uses.

Usually, DoS attacks are closely related to brute force attacks. The brute force attack uses all combinations of possible characters or dictionary word lists to try find out any passwords on the system (eg root accounts). When a root account in a network is found out, any DoS attacks can be done easily over the specific network.

Here are some of the most known DoS attacks:

1. SYN Floods Continue Reading…

Why you need DHCP server?

DHCP is useful for fast delivery of client network configuration. When configuring the client system, the administrator can choose DHCP and not have to enter an IP address, netmask, gateway, or DNS servers. The client retrieves this information from the DHCP server.
DHCP is also useful if an administrator wants to change the IP addresses of a large number of systems. Instead of reconfiguring all the systems, he can just edit one DHCP configuration file on the server for the new set of IP address. If the DNS servers for an organization changes, the changes are made on the DHCP server, not on the DHCP clients. Once the network is restarted on the clients (or the clients are rebooted), the changes will take effect.

Step 1. Installing DHCP server

#apt-get install dhcp3-server

Once you press enter installation will start it will ask you some questions just you need to click ok for all three times

Step 2. Configuring DHCP server

The main Configuration file for DHCP server is

/etc/dhcp3/dhcpd.conf

Before doing any changes take backup copy of this file and add the following lines
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