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What is DHCP, and why do we use it?

Assigning IP addresses is not an easy task, and a human admin might get confused in the process. This confusion would result in the loss of an internet connection for someone. But DHCP comes to the rescue in this case.

Paulius Ilevičius

Paulius Ilevičius

Apr 12, 2022 · 3 min read

What is DHCP, and why do we use it?

DHCP definition

DHCP (or Dynamic Host Configuration Protocol) is a network management protocol that automatically assigns IP addresses and other communication parameters to devices connected to a network. For example, a router usually acts as a DHCP server in most home networks. It assigns IP addresses to your devices.

DHCP makes the work of network administrators easy. If it didn’t exist, they would have to assign IP addresses manually, which would be inefficient, time-consuming, and error prone.

How does DCHP work?

When a device joins a network, it requests an IP address. The request then travels to a DHCP server. A server assigns an address, monitors its usage, and takes it back after the device is shut down. The same IP address can then be reassigned to another device. A device can use this address to communicate with internal and public networks.

DHCP servers also provide DHCP parameters, also known as DHCP options. They describe various factors of IP addresses; for example, how long they can be used. DHCP options usually define:

  • A default gateway that routes data back and forth between the local network and the internet.
  • A subnet mask that separates host addresses and network addresses within an IP address.
  • A DNS server that translates the names of IP addresses into the ones we remember.

DHCP has three methods of IP address allocation:

  • Dynamic allocation. Dynamic allocation takes place when an admin reserves IP addresses for DHCP. Then each DHCP client on the local network requests an IP from the DHCP server during the network initialization phase. The whole process takes place during a controllable amount of time that allows a DHCP server to reclaim and reallocate an unused IP address.
  • Automatic allocation. A DHCP server permanently allocates an IP address to a client under the rules set by an administrator. It differs from dynamic allocation because a DHCP server has the data of the previous IP assignment and can reassign the same IP to the same client.
  • Manual allocation. In this case, an administrator manually assigns a unique identifier for each client to an IP address. A DHCP server is usually configured to switch to another method if manual allocation fails.

Benefits of DHCP

Reasons we use DHCP:

  • Reliable IP address configuration. DHCP helps to prevent conflict between two users with the same IP address. Such conflict would block both users from connecting to the internet. DHCP resolves such conflicts automatically without the possibility of human error.
  • Mobility. DHCP also ensures mobility. Users can use their mobile devices anywhere within the range of their network.
  • More efficient network administration. DHCP centralizes the whole IP configuration, and separate IP-assigning servers are not needed.
  • Flexibility of IP schemes. DHCP makes changes of IP address schemes easier and without disruptions to end users.

DHCP security concerns

DHCP doesn’t have any authentication, so it is vulnerable to cyberattacks. DHCP can be exploited in the following ways:

  • Unauthorized DHCP servers can provide false information to clients.
  • Unauthorized clients can also intercept DHCP servers and obtain access to resources.
  • Malicious clients can also exhaust DHCP resources.

All these issues can result in DDoS and man-in-the-middle attacks. However, admins can reduce the risk by using the relay agent information option and tagging DHCP messages when they arrive. They can also use network access control to protect DHCP.

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