What is DHCP?

If you’re looking for something that can help automate and centralize the management of IP address distribution, DHCP may be for you. In this resource, you’ll learn all about this protocol, including how it works and the pros and cons of using it.

DHCP Explained

DHCP stands for Dynamic Host Configuration Protocol. This protocol dynamically assigns or leases unique IP addresses for devices (clients) on a network. DHCP also allocates the subnet masks and default gateway addresses for a network. In many cases, routers function as a DHCP server, but they could also be a computer. Before DHCP, network administrators often relied on software like Excel to manage large volumes of IP addresses. On top of that, they all had to be assigned and tracked manually. You can imagine how fun that is! Aside from the headache of such a task, manual assignment increases the margin of error. With DHCP implemented into a network, IP addresses are automatically assigned.

DHCP Terms and Definitions

Before we go any further, there are a few terms you should know:

DHCPDiscover: The packet sent from a client or device when connecting to a DHCP network.

DHCPOffer: A DHCP Offer includes predefined rules and settings, as well as an assigned IP address.

DHCPRequest: This refers to when a client asks for permission to use an IP.

DHCP Reservation: A predefined range of IP addresses for a network.

DHCPACK: An Ack (acknowledgment) is confirmation that a device can receive an IP and connect to a network.

DHCPNACK: A Nack (negative acknowledgment) is when a device is denied an IP.

How Does DHCP Work?

Now that all the terminology is out of the way, let’s get into how DHCP works. This protocol gives you full control over the usable amount of IP addresses in your network. The way this works is by assigning IP ranges. Think of this like a block of rooms reserved at a hotel for an event. You’re just reserving a block of IPs for devices (guests) that connect to your network (hotel). The number of IPs available will depend on your network’s router.

Each time a device connects to a DHCP-enabled network, it sends a DHCPDiscover packet to the server. This is the device’s way into a network. After receiving the signal, the server returns a DHCPOffer. Once the client receives the offer, it sends back an official request to connect to the IP. The DHCP server then sends an ACK or “signs off” on the request, and the client is now connected to the network. If the requesting device doesn’t meet the criteria for the network, the DHCP server will return a NACK. 

Devices That Can Be on a DHCP Network

Here are some common devices that connect to DHCP networks.

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Static vs Dynamic IP Assignment

Dynamic IP addresses are IPs that periodically change. The DHCP server retrieves IPs from a block of addresses set up by a network administrator. This works the same for home networks, except an internet service provider (ISP) supplies the IPs. In a business setting, it’s not uncommon for a device to receive a new IP address every time it connects to a DHCP network. 

While dynamic assignment of IP addresses is ideal for many devices on a DHCP network, some IPs are better off static. Static IP addresses are manually assigned IPs that do not change. Printers or remote file servers are good examples. If these types of clients have dynamic IP addresses, each connected device would require setting updates every time the IP for the printer or server changed. Not everyone understands how DHCP configurations work, and it may not be possible for IT administrators to be present at all locations. Because of this, it’s a good idea to use static IP or DHCP reservations for certain devices.

DHCP Reservations

If you want a device to keep the same IP address or need to set up port forwarding, you can use DHCP reservations. These reservations are pre-set IP addresses for specific clients. They work the same as regular DHCP IP assignments but are considered “permanent” leases. Using reservations is a huge timesaver, especially if a device gets frequent firmware updates. However, some routers require a device’s MAC address to make a reservation.

Pros and Cons of DHCP

We’ve covered most of the pros of DHCP already, but here’s a list of them for quick reference. 

• Manage IP addresses from one place
• Automatic assignment of dynamic IPs
• Smaller chance that two devices will use the same IP address
• Allows for quick, on-the-fly changes
• You don’t have to be onsite to make changes to devices on the network
  

Now, here is a list of DHCP disadvantages:

• If you assign too few IP addresses, you can prevent devices from making a connection. 
• Devices must support DHCP configurations. If the DHCP server for the network is down, the connected device will also be down.
• If a random DHCP shows up on your network, you may experience communication issues.
• Devices must be properly configured to connect to the network
  

The TL;DR of DHCP

Dynamic Host Configuration Protocol (DHCP) is a network protocol that automatically assigns IP addresses and any corresponding information to each host on a network. This allows endpoints to communicate more efficiently and simplifies IP management. DHCP also defines related configuration variables and allocates the subnet masks and default gateway addresses for a network. Because IP addresses using DHCP are generated automatically rather than manually, networks are less prone to experiencing errors.

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