DHCP Server: Definition, Functions, and How It Works

What Is DHCP Server?

A DHCP server is a service that automatically configures IP addresses and other network information for computer devices connected to a network. DHCP stands for Dynamic Host Configuration Protocol.

In this context, an IP address is a unique identifier for each device connected to a network. With an IP address, devices have access to websites, emails, and more.

So, what is DHCP server and what is its role in network management? This server plays a role in administering and automatically assigning IP addresses to each device, reducing time and effort without the need for manual configuration.

How Does A DHCP Server Work

Besides understanding the definition, you also need to comprehend how this service works. The server's operation involves dynamic processes in configuring and distributing IP addresses to client devices connected to the network.

Here is a comprehensive explanation:

1. Client Accesses the Network for the First Time Without a DHCP Server

Do you know what will happen when a new client connects? In this process, the client goes through four stages of DHCP message exchange:

1. Discovery: When an uninitialized client device accesses the network for the first time, it sends a "DHCPDISCOVER" message to the IP address 255.255.255.255 via broadcast to the entire network. This message includes the client's MAC address, a list of requested parameters, and broadcast flags. The purpose is to locate a DHCP server on the network. 
2. Offer: Upon receiving the "DHCPDISCOVER" message from the client, the server responds with a "DHCPOFFER" message. This message contains a network configuration offer, including a valid and available IP address from the IP address pool.
3. Request: After receiving the "DHCPOFFER" message, the client acknowledges it and broadcasts a “DHCPREQUEST” message. This message includes the server identifier to indicate the selected server and the requested IP address. Servers not chosen by the client will allocate the address to other clients.
4. Acknowledgement: Following these steps, the DHCP responds with a “DHCPACK” message to confirm the successful application of the network configuration. The client device can now communicate within the network using the assigned IP address.

2. Client Accesses the Network for the First Time Using a DHCP Server

The difference lies in the server's role in relaying DHCP messages between the server and the client. Here is the complete explanation:

1. Discovery: Upon receiving a "DHCPDISCOVER" message broadcasted by the client, this server will examine the suitability of the hop field value in the message, which must be greater than 16, and the giaddr field value in the message, which must be 0. The server will then change the destination IP address of the "DHCPDISCOVER" message to the server's IP address.
2. Offer: DHCP will receive the "DHCPDISCOVER" message from the client device and respond with a "DHCPOFFER" message containing a network configuration offer. After receiving the "DHCPOFFER" message, the server will check the compatibility of the recipient's giaddr field value, which should be an IP address, and the flags field value, which should be 1.
3. Request: At this stage, the message exchange process between the DHCO server and the client accesses the network for the first time without using a DHCP. 
4. Acknowledgement: Subsequently, the server will receive the “DHCPACK” message.

3. Client Reuses IP Address

Now, do you know how the process works when a client reconnects to a previously allocated IP address? At this point, the client will exchange messages with the server to regain network parameters.

This process is carried out in two stages, as follows::

1. Request: When a client device that has obtained an IP address from the DHCP Server restarts or temporarily disconnects from the network, it will request an extension of the lease for the previously received IP address. To do so, the client device will send a “DHCPREQUEST” message to confirm to the server that the IP address is still usable. 
2. Acknowledgement: DHCP will respond with a DHCP ACK message to confirm that the used IP address is still valid and available for use by the client device. If the client device does not request an extension of the lease, it will release the IP address and add it back to the pool of available IP addresses.

DHCP Server Function

Understanding what a DHCP is and how it works is barely sufficient. It is because you also need to comprehend its functions, especially in network management.

Here is an explanation of the main functions:

1. Managing and Distributing IP Addresses

One of the main purposes of this service is to manage and distribute IP addresses to devices connected to the network.

When a new device joins the network, the server automatically assigns an available IP address to that device.

This automated process makes IP address administration easier.

2. Preventing IP Address Conflicts 

One issue that can arise with IP addresses is the potential for two devices to have the same address.

By using this server, this service ensures that an IP address has not been used before when a device requests a new address.

DHCP may prevent IP address duplication, which can lead to communication problems and conflicts within the network.

3. Automatically Renewing IP Addresses

Each IP address assigned to a client device has a predetermined lease extension.

After the lease extension expires, the client device needs to renew or refresh the address from the server.

If the client device doesn't renew the IP address, the server will allocate that address to another device in need. 

4. Supporting IP Address Reuse

Now, you also need to know the function of DHCP server in network management. It can support the reuse of previously used IP addresses.

When a device leaves the network or becomes inactive, the IP address previously assigned to that device can be released and returned to the pool of available IP addresses. Therefore, the IP address can be reused by devices joining the network.