The Simple Definition
Dynamic Host Configuration Protocol (DHCP) is a network protocol used to automatically assign IP addresses to devices on a network. DHCP is used to simplify the management of IP addresses and reduce the likelihood of IP address conflicts.
When a device, such as a computer or a smartphone, connects to a network, it sends out a broadcast message requesting an IP address. A DHCP server, which is typically located on a router or a dedicated server, receives the request and assigns an available IP address to the device. The DHCP server also assigns other network configuration information, such as the subnet mask, default gateway, and DNS server IP addresses.
One of the key benefits of DHCP is that it eliminates the need for manual configuration of IP addresses. This makes it easier to add new devices to a network and to move devices between networks. DHCP also allows for the efficient use of IP addresses by recycling addresses that are no longer in use.
There are a few different DHCP options that can be configured. One of the most common is DHCP reservation, which allows for a specific IP address to be permanently assigned to a device. This is useful for servers and other devices that need a static IP address. DHCP also allows for IP address leasing, which means that an IP address is assigned to a device for a specific period of time, after which the device must request a new IP address. This is useful for devices that are only occasionally connected to the network.
The DORA Process
To understand how DHCP works, we will go over the DORA process (Discover, Offer, Request, Acknowledge) is the process that DHCP uses to assign IP addresses to devices on a network.
Discover: When a device connects to a network, it sends out a broadcast message called a DHCP discover packet. This packet is sent to the broadcast address (255.255.255.255) and to the DHCP server port (67) to find a DHCP server on the network.
Offer: When the DHCP server receives the discover packet, it sends a DHCP offer packet back to the device. The offer packet contains the IP address, subnet mask, default gateway, and other network configuration information that the DHCP server is offering to the device.
Request: The device receives the offer packet and sends a DHCP request packet back to the DHCP server to request the IP address and other configuration information that was offered.
Acknowledge: The DHCP server receives the request packet and sends a DHCP acknowledge packet back to the device to confirm that the IP address and other configuration information have been assigned. The device then uses this information to configure its network settings and start communicating on the network.
It is worth noting that DHCP also allows for IP address leasing, which means that an IP address is assigned to a device for a specific period of time, after which the device must request a new IP address.
About the Author:
Andres Sarmiento, CCIE # 53520
With over 18 years of professional experience, Andres is a specialist in Unified Communications and Collaboration technologies, Enterprise Networks, and Network Security. He has consulted for numerous companies in South Florida, including Financial Institutions, on behalf of Cisco Systems. Andres has played a key role in several high-profile implementations, utilizing Cisco technologies such as Data Center, UC & Collaboration, Contact Center Express, Routing & Switching, Security, and Hosted IPT Service Provider infrastructures.