The Dynamic Host Configuration Protocol, abbreviated to DHCP, is a protocol defined in 1993 that is now firmly integrated in modern IT infrastructures. The protocol enables newly integrated devices in the network to be configured automatically. This includes the dynamic assignment of IP addresses and other configurations such as the network mask. How exactly DHCP works and what you need to know about it can be read in the following.
What is DHCP and what does it do?
In order to gain an understanding of the necessity and the functional principle of the Dynamic Host Configuration Protocol, the following questions need to be answered. How do you recognize a device in a network? Which device belongs to your own home network and which to the Internet? Such questions can be answered with terms such as IP address, subnet masks or DNS servers. The standard protocol DHCP exists so that the assignment of the configuration parameters is possible in the first place. This allows network administrators, such as the IT administrators of your company, to assign the IP addresses in the company network automatically and centrally. Every device connected to the network, be it a computer, smartphone or tablet, is assigned a unique IP address via DHCP.In addition, DHCP also manages the following configurations:
- Net mask or subnet mask: Addressing of the network or host part within the IP address.
- Gateway: component that creates a connection between two systems.
- Domain Name System server (DNS server): Answers requests for name resolution on the Internet. Without this, you have to know the associated IP addresses by heart instead of domains, for example.
- Time and NTP server: synchronization of the time.
Without the protocol, the network administrator would have to make these settings manually on each computer. The main advantage of DHCP is that it is easy to use and configure the network parameters.
What is a DHCP Server?
The DHCP server is a background process and waits on UDP port 67 for a request from a DHCP client that wants to connect to the network. The required parameters are located in a previously defined configuration file, which are then automatically sent to the client in order to configure it. There are three different operating modes of a DHCP server:
- Manual assignment: Also known as statistical DHCP. The IP addresses specified on the DHCP server are assigned fixed MAC addresses (the hardware address of the individual network adapter - for unique identification of the device). The addresses are permanently assigned and there is the disadvantage that no additional clients can be integrated into the network, since the addresses are only permanently assigned. However, this can also be desirable from a security perspective.
- Automatic assignment: With this assignment, a defined range of IP addresses is assigned by the DHCP server. As soon as the addresses are linked, they also remain linked indefinitely. The disadvantage is that new clients do not receive an IP address if the area is completely assigned.
- Dynamic assignment: In contrast to the two previous methods, the assignment is limited in time with dynamic assignment. This means that the DHCP server specifies in its configuration file how long an IP address can be given to a client. This time set by the administrator is also referred to in IT as "lease time".
