What DHCP is and Types of DHCP Explained

Every device in an IP network requires a valid IP configuration. There are two ways to configure IP configuration to a device: manually and dynamically. In the manual method, we manually assign IP configuration to devices. In the dynamic method, we configure the DHCP service. The DHCP service automatically provides IP configuration to devices.

If your network size is small, you can use the manual method to configure and manage IP addresses on all devices. But, if your network size is big, the manual method will not work for you.

Let's understand it through an example.

Suppose you are a network administrator in a company that has more than 2000 devices in its network. The company bought a new Internet connection and asked you to configure all devices to use the new Internet connection.

Depending on how you previously configured the IP configuration on all devices, this could be an easy or difficult task for you. If you manually configured the IP addresses on all devices, you need to configure all devices again. However, if you used DHCP, then you only need to change the configuration on the DHCP server. When the clients reboot or renew their IP configuration, they will automatically acquire the new IP configuration from the DHCP server.

What is DHCP?

DHCP is a service. It provides an easy way to manage IP configuration. It allows devices to acquire their IP configuration dynamically. It is defined in RFC 2131 and 2939. It works in the server/client model. The server offers and delivers IP configurations. Clients request and acquire their IP configurations. It works on all types of networks. You can use DHCP in your home network or can use it in your office or business network.

DHCP Address Allocation Methods

To provide an IP configuration, a DHCP server can use three mechanisms. These mechanisms are the following.

Static allocation

In this method, the administrator configures an allocation table on the DHCP server. In this table, the administrator adds the MAC addresses of all clients and assigns an IP configuration to each client.

The DHCP server uses this table to provide IP configurations. When a client requests an IP configuration, the DHCP server finds the client's MAC address in the table. If it finds an entry for the client, it provides the IP configuration to the client.

Dynamic allocation

In this method, the administrator configures a range of IP addresses on the DHCP server. The DHCP server assigns an IP configuration from the configured range to each client that requests an IP configuration.

In this method, DHCP offers the IP configuration only for a specific time, known as the lease. The IP configuration remains valid until the lease duration is over. Once the lease duration is over, the client is required to obtain a new IP configuration from the server again.

Automatic allocation

This method is similar to the dynamic method. In this method, the administrator configures a range of IP addresses on the DHCP server, and the DHCP server assigns an IP configuration from the configured range to each client that requests an IP configuration.

In this method, the DHCP server assigns the IP configuration permanently. For this, the DHCP server sets the lease duration to infinite. As a result, once the DHCP server chooses an IP configuration from the pool and assigns the IP configuration to a client, the IP configuration remains with that same client indefinitely.