Posted on 3 Comments

How to enable DHCP server in VirtualBox

Good evening friends. We have seen how to create a virtual pentest lab both in Oracle VirtualBox (see here) and Vmware Workstation(see here). Although both penetration testing labs  were almost similar, there is a small difference between them . As the title of this howto already implies it is the absence of DHCP server in the pentest lab we created using Virtualbox. VirtualBox provides a DHCP server but it can’t be turned on using the GUI feature unlike Vmware Workstation. So let’s see how to enable DHCP server in Virtualbox networks. I am going to assign DHCP server to my pentest lab I created above. I will assume that  virtualbox is installed on Windows. Open CMD and navigate to the directory where  Virtualbox is installed. By default it will be “C:Program Files OracleVirtualBox”. Type the command “vboxmanage dhcpserver add –ip –netmask –lowerip –upperip –netname pentestlab”. Hit Enter.

In the above command, “vboxmanage dhcpserver  add –ip” starts a DHCP server with IP address . The “–netmask″ assigns subnet mask for the network. The “–lowerip” and “–upperip” options assign a lower ip address and upper ip address respectively.   The “–enable” option enables the DHCP server we just created. The “–netname” option assigns a name to the network. Now we have successfully created an internal network named pentest lab with its own DHCP server. Now change the network adapter settings of the attacker machine ( Kali Linux ) to pentest lab.

Similarly change the network settings of the victim machine.

Now start the attacker machine (Kali Linux) to see if the IP address is automatically assigned. If the IP address has not been assigned, disable the adapter using command “ifdown eth0″ and re enable it by typing command “ifup eth0″. Now check if the IP address has been assigned or not by typing command “ifconfig”.

Similarly check on the victim machine.

We can see that the IP addresses have been automatically assigned successfully starting from the range of Hope this was helpful.

Posted on Leave a comment

How to subnet a network

Understanding subnetting is very important not only for those preparing for CCNA exam but also network administrators. Today, I am going to teach you how to create a subnet in a network. For this, I will use Packet Tracer software. To know what is subnetting and why we need it go here. So let’s start.

Imagine I formed a small software company named shunya whose network looks like below. I hired one Java developer, one software tester, one HR and one network administrator. I have been assigned the IP address range from to

I have enabled DHCP on my router as below.

After one year, imagine my company has received Abrahamic blessings from GOD and has seen rapid growth. Now the company has three Java developers, three software testers and  a dedicated HR team. Not only that, my company now has moved into Remote Infrastructure Management(RIM) and has a Network Operation Center(NOC) and Security Operation Center(SOC).  Total I have 15 computers in my network which looks like below.

Now see the image below. Here the machine “JD1″ sends a packet to machine “Testing3″. We can see here that for communication between machines “JD1: and “Testing3″ other machines have also been disturbed.

So for this reason, I decided to subnet the network. I decide to divide the network into three subnets as shown below.

To create a subnet, first we need to have proper planning as to how many subnets we need and how many we may need in the future. Presently, I need three subnets. The number of subnets should always be calculated in the powers of 2.

2 to the power of 1 = 2

This doesn’t satisfy our requirement as we need three subnets.

2 to the power of 2 = 4

This satisfies our requirement. So we need to take two bits from the host portion of the IP address. to is the address range available to us with subnet mask,  Writing the subnet mask in the binary notation, it is

11111111 11111111 11111111 00000000

 255            255          255             0  

The first 24 bits are network bits and the last eight bits are host bits. To create three subnets, we need to take two bits from the host portion of the address as explained above.

11111111 111111111 11111111 11000000

   255              255            255         192

Four subnets which can be created from the above subnet mask are, to ( with host bits 00000000 ) to ( with host bits 01000000 ) to ( with host bits 10000000 ) to ( with host bits 11000000 )

Since we require only three subnets, we will create the first three subnets. The first subnet ( to ) comprises of Java Developers and Software testers. The commands are as below on the interface.

If you go to any machine on this subnet and look at its IP address, it will be like below.

Now the subnet for the Human Resource Department ( to ) . This will be like below.

The third subnet ( to ) comprises of NOC and SOC.

Now our network has been successfully sub netted into three subnets and we still have another subnet to use for future use.

Hope this was helpful. If you have any doubts regarding this article please comment below. Thank you.