Question

Why do we need DHCP and how does it work? Explain using your language (briefly, step by step).

Answer 1

DHCP stands for Dynamic Host Control Protocol is a network management protocol used to assign IP addresses and other network parameters(submask,gateway,DNS addresses) to every host in the network dynamically.

Why Do we need DHCP:

Every computer or a device on a network has to have an IP address for communication purpose. An IP address is an identifier for a computer device on a network.

There are two ways to assign an IP address.

They are: 1)Static 2)Dynamic

In static the user assigns the IP address manually. For each computer on a network we have to type in IP address, subnetmask, default gateway and a DNS server manually. We have to do this for all the other hosts.

Let's assume there is a network with a thousand number of hosts. We have to a assign and configure each host with a unique and valid IP address, default gateway and DNS server so that they can communicate with each other. The IP address has to be unique. If we assign same IP address to two hosts it would caiuse an IP conflict. And those computers will not have access to network. It will be a difficult task to assign IP addresses manually to all the thousand hosts. So, here we require a DHCP server which assigns IP addresses to all the hosts dynamically.

      In DHCP a computer or device gets it IP automatically from a DHCP server. The DHCP server assigns subnet mask,DNS server, Default gateway to the host in addition to the IP address.

How does it work:

DHCP involves a client and a Server. The computer or the devices are clients which requests for the IP address. The server assigns IP addresses.

Step1:

when a device is connected to the network first the DHCP client broadcasts a DHCPDISCOVER message to the network.

Step2:

The message is then received by the DHCP server and the server responds with DHCPOFFER message. The message includes the IP address, subnetmask, default gateway, DNS server and expiry date.

Step3:

After receiving the DHCPOFFER the client replies with DHCPREQUEST which means it is accepting the Network parameters.

Step4:

Now the server replies with DHCPACK which is an acknowledgement packet which means it is stroring the IP address and ther details in its DHCP database.

Now the deviece has an IP address.

when assigning the IP addresses the DHCP server assigns them with an expity date. So, that it can tack back the IP address of the hosts which are not functional and re-assign the address to another host. If the Host wants to keep the IP address then It has to request a renewal from the server after the expiry date.

In DHCP the client uses port 68 and server uses port 67.