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What is a DHCP Server?

Author avatar - Jason Wynn

Jason Wynn

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Datacenter networking servers

A DHCP Server is a network device that automatically assigns IP addresses and other network settings to endpoints. DHCP servers have simplified networking since the early 1990s, providing IT admins with the ability to automate IP address assignment.

The world of manually assigning static IP addresses to network devices is a thing of the past. And DHCP servers continue to support this process as the Internet moves from IPv4 to IPv6. How does it all work? Let’s find out!

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What is DHCP

DHCP or Dynamic Host Configuration Protocol is a client and a server protocol that automatically provides an Internet protocol (IP) address and other related information such as the subnet mask and the default gateway to network endpoints.

A DHCP Server is the device that provides this solution. Either as a physical or a virtual server, it can be a network appliance. Without a DHCP server, network administrators would need to manually set up every client that joins the network, which would be very time consuming, particularly in large networks.

How does DHCP work

DHCP runs at the application layer of the Transmission Control Protocol/Internet Protocol (TCP/IP) stack to dynamically assign IP addresses to Dynamic Host Configuration Protocol clients and to allocate TCP/IP configuration information to those Dynamic Host Configuration Protocol clients.

When a Dynamic Host Configuration Protocol server receives the message from the endpoint, it also broadcasts a DHCP offer message over the Ethernet network, informing the endpoint that it is available.

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DHCP is made up of some key components:

Table 1 – Components of DHCP

DHCP component Function
DHCP Servers A server or a router that holds the network information
DHCP Client An endpoint, whether it’s an Apple iPhone, Windows 11 PC, hard-wired camera into the network, all endpoints require the configuration information received from the server
DHCP Relay Agent DHCP servers provide requests for the network segment which it looks after.  DHCP requests can’t span across different local area networks (LAN), a Relay Agent allows for the DHCP server to provide for multiple LAN’s and will forward the requests to the servers
IP Address Pools Lists of all the IP addresses that can be assigned to the endpoints
Lease Times The time in which an IP address can be allocated to an endpoint is done through the lease time. This prevents endpoints from holding onto the IP address indefinitely. Once the lease is up, the device can then renegotiate with the server to ensure the IP address is either retained or moved to another suitable IP address
Subnet Mask Informs the endpoint what network it is currently presented with. Networks are segmented using subnet masks
Gateway Addresses Tells the endpoint where to find the network gateway to connect to the Internet or how to connect to another adjoining network

DHCP advantages

One of the key advantages is you no longer need to worry about duplicate/multiple endpoints using the same IP addresses. We are human, we make mistakes, DHCP servers take this mismatch away from us.

The deployment of DHCP is meant to be easier, far easier than it was back in 1993! We can implement the automatic assignment of IP addresses, meaning that it’s vastly more accurate.

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The manual configuration of subnet masks, gateways, IP addresses on a static method is no longer required and network engineers and administrators can move their interests into something much more worthwhile. The configuration is obtained the same by all users whether the endpoint is static or mobile, whether they are attached for minutes or months. The network configuration is obtained automatically when devices change their network.

Other benefits of DHCP Servers include:

  • IP Address Management: If you decide against using a DHCP server, you’ll instead need to make sure you have the resource and time to manually move clients to subnets without the need for human interaction at all. All the network information is passed to the client from the DHCP server, so no manual work is required at all.
  • Centralized network client configuration: If you need a range of different configurations for each client, you can create client groups, so each has different setups according to your business requirements. All this information is saved in the DHCP data store, and this is where the configuration can be changed to roll out to all clients, without having to change them manually.
  • Large network support: DHCP is especially advantageous to networks with millions of DHCP clients, as they can use the server over multithreading to process many client requests simultaneously. The server also supports data stores that are optimized to handle large amounts of data. Data storage access is handled by separate processing modules and thus enables you to add support for any database that you require.

DHCP disadvantages

DHCP isn’t perfect, and here are some of the DHCP issues you might encounter:

  • NAT: As an avid gamer I often get caught out with NAT – or Network Address Translation – NAT is used to translate a source address or a destination address as it traverses layer 3 network boundaries. Networked gaming and video conferencing do not like to have a NAT or worse Double NAT. Avoid traversing networks with a double NAT where possible.
  • Security Issues: Like almost anything these days, you should be aware that using DHCP automation can be a serious security risk. For instance, if a rogue DHCP Server is introduced to the network. This can happen if it isn’t under the control of the network staff and can offer IP addresses to users connecting to the network. If a user connects to the rogue DHCP Server, information sent over that connection can be intercepted and looked at by unauthorized people, violating user privacy and network security, a technique known as a man in the middle attack.
  • Failure: Failure of the network can arise if only a single DHCP server is in place, as it forms a single critical junction where failure can erupt from a single issue to a system-wide problem. If the server fails, any connected computers that don’t already have an IP address will try and fail to obtain one. Computers that already have an IP address from before the server’s failure will attempt to renew it, which will lead to the computer losing its IP address, meaning complete network access loss until the server is restored.

Learn more about DHCP

DHCP is a way of life for the world of IT administration. DHCP will be with us for as long as we continue to use IPv4, and we are likely to see it within IPv6 too. There is no getting away from the use of DHCP for large network administrators.

Microsoft continues to provide exams such as Networking Fundamentals and will continue to create new exams for as long as we require computers to be networked together. Windows Server can also be set up as a DHCP Server. In addition, sources such as CompTIA also provide accreditation in the Network+ exam provide a vendor-agnostic approach to further education and accreditation. Good Luck on your path ahead!

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