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DHCP (Dynamic Host Configuration Protocol): How Does it Work?


DHCP stands for Dynamic Host Configuration Protocol. Because of the decide suggests, this protocol is used to dynamically assign an IP care for to a mannequin new consumer in a neighborhood.

So, in case you are already conscious about TCP/IP, you already know that each one the neighborhood gadgets require an IP care for to speak inside a neighborhood. Before DHCP, gadgets used to have statically assigned IP addresses. The neighborhood admin wished to assign an IP care for to each gadget on a neighborhood utilizing neighborhood configuration administration panel. Later, with the assistance of DHCP, it turned easier to care for a whole lot of gadgets in a neighborhood dynamically.

Sure terminologies are related to DHCP. Allow us to attempt them.

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A scope is a wide range of IP addressed from the place a DHCP server assigns an IP care for dynamically to fully fully completely different gadgets coming into the neighborhood.


If the DHCP (Dynamic Host Configuration Protocol) server has the scope of personal IP addresses from to, it’d solely accommodate 100 gadgets at a time, and an IP care for is dynamically assigned to a mannequin new gadget transferring into the neighborhood.


In a neighborhood, furthermore it is potential neighborhood gadget can’t be assigned a dynamic IP care for. For instance, the IP care for of a default gateway can’t be modified very steadily on account of it would influence the entire neighborhood. That’s why the considered reservation obtained proper right here in DHCP. Utilizing reservations, we’re going to inform the DHCP server to order numerous of the IP addresses and don’t use these in dynamic assigning.


Leasing is the technique of dynamically assigning an IP care for to a mannequin new consumer contained in the neighborhood for a troublesome and fast interval. After the leasing time expires, the gadget every requests for one more IP care for or the an equivalent IP care for to be allotted to it.

How does DHCP work?

When a mannequin new consumer have to be part of the neighborhood, it has to endure constructive steps of negotiations. Listed beneath are these steps:

DHCP Uncover

When a mannequin new consumer tries to affix a neighborhood, it has no particulars regarding the neighborhood. So to get further knowledge, the client will broadcast a DHCP Uncover packet into the neighborhood. This packet is obtained by every of the nodes contained in the neighborhood.

The availability care for contained in the DHCP Uncover packet shall be on account of the mannequin new consumer continues to be not conscious about its IP care for. Nonetheless, the client will ship its MAC care for contained in the DHCP Uncover packet.

Whenever you’re efficiently conscious about the data hyperlink layer from the OSI mannequin then, utilizing MAC care for solely the communication occurs at layer two, i.e., the ethernet layer.

DHCP Current

There’s moreover just a few DHCP server on a neighborhood. When all servers obtain the DHCP Uncover packet, they know new machine should affix the neighborhood.

Thus, all of the DHCP servers reply by sending DHCP current packet. This packet accommodates an IP care for being supplied by the DHCP server. Upon receiving the DHCP current packets, it’s as so much as a result of the mannequin new machine to resolve on a proposal.

The DHCP (Dynamic Host Configuration Protocol) current packet accommodates the next knowledge:

  • Shopper’s MAC care for
  • The supplied IP care for
  • Subnet masks of the neighborhood
  • The lease interval
  • IP care for of the server making the current

DHCP Request

After receiving lots of DHCP current messages from fully fully completely different DHCP servers, the mannequin new consumer will select one DHCP server current, and it’ll notify the DHCP server by broadcasting utilizing the DHCP request message. That is so on account of all of the DHCP servers moreover should know that the mannequin new consumer has accepted a server’s current. In order that, others don’t attempt to sustain themselves engaged.


Upon receiving the DHCP request packet, the server sends an acknowledgment utilizing the DHCP ACK packet. The server furthermore makes certain that the IP care for allotted to the mannequin new machine shouldn’t be allotted to a different consumer contained in the neighborhood.

DHCP ACK packet accommodates fully completely different neighborhood particulars equal to IP care for, router care for, subnet masks, and loads of others. Because of the client receives this packet, the client configures itself.

DHCP Processes

Other than the above 4 steps, there are fully completely different auxiliary DHCP messages as efficiently which helps a neighborhood administrator in organizing the neighborhood.

DHCP Launch

DHCP launch packet is used largely when a consumer goes to go away the neighborhood. DHCP launch is used to launch the connection and allocate the IP care for as soon as extra into the scope, or in easy phrases, the lease expires.

DHCP Inform

The DHCP reservations that we examine at first of the article is configured utilizing DHCP inform message. DHCP inform message is used when the neighborhood administrator has manually configured a machine. On this case, the server is educated to order that IP care for and chorus from assigning it to anybody.

DHCP relay agent

If lots of native home networks (LANs) have only one DHCP server, then DHCP relay agent helps in forwarding the DHCP request to a DHCP server and transmitting the response as soon as extra to the client. That’s on account of a consumer gadget (with out an IP care for) can’t talk about with the DHCP server instantly if the server isn’t current on the client’s native neighborhood.

Reliability in DHCP (Dynamic Host Configuration Protocol)

DHCP ensures reliability utilizing two strategies.

  • Renewal and,
  • Rebinding

DHCP Renewal

To make sure that a specific consumer doesn’t over revenue from the neighborhood for extended and others furthermore get a risk, DHCP makes use of renewal to confirm reliability. As shortly as half of the lease time has elapsed, every consumer has to ship DHCP request as quickly as additional to get a mannequin new IP care for or proceed utilizing the an equivalent IP care for. If the server is unreachable then, the client retains on attempting till the server replies.

DHCP Rebinding

In some cases, the DHCP server fails to answer. In that case, the client tries to contact the backup server. In each different case, it would rebroadcast the DHCP request to all of the DHCP servers contained in the neighborhood. If rebinding fails, then the lease will get expired, and the client ought to start out the DHCP course of 1 different time.

I hope you actually appreciated studying it.