What Is DHCP?

DHCP is the short for Dynamic Host Configuration Protocol .Its purpose is to assign dynamic IP addresses to devices on a network. Dynamic addressing means that a device can have a different IP address everytime it connects to the network.

In short, DHCP allows a computer to join a network without having a pre-configured IP address. It assigns unique IPs to computer devices and then releases and renews them every time the machine leaves and reconnects to the network.

DHCP features include allowing the user to define “pools” of IP addresses (DHCP terminology calls them scopes). The IP addresses are handed out by the server together with the related configuration settings like subnet mask (defines the boundaries of an IP subnet – grouping of connected network devices). DHCP also makes it easier for a client to move the computer from one subnet to another because it allocates IPs according to the subnet the request came from. Due to the dynamic allocation of the IPs, it is easy to recover the addresses that are no longer used and put them back in the unallocated scope.

 

he lease for allocating the IP to a certain computer in the network is a period of time during which the allocated IP is valid. After the lease period expires, the request for renewing the lease is sent to the DHCP server and a new IP is obtained. Largely put, the DHCP client sends a broadcast packet on the network with a DHCP request. The DHCP server picks up the request and allocates to the PC the IP address from the scopes available. The address is not allocated permanently (DHCP assigns dynamic IP addresses) and the IP is leased to the client. When the lease period expires, the client sends an IP lease renewal message.

The scopes or IP address “pools” are administrative grouping of IP addresses for computers on a subnet that are using the DHCP service. Configuring them implies defining some parameters used by clients, like the range of IPs (IP “pool” or scopes) from which to include or exclude addresses used for IP leases, the subnet mask, the scope name, etc.

The downfall of DHCP service in the case of routers of small networks is that the IP will be assigned to any device connecting to the network. The issue is significantly important when it comes to wireless devices. A wireless device in the range of your router will be automatically assigned an IP. Fortunately, there is a solution for this problem and that consists in turning off the DHCP. This way, you will be able to protect your network from unwanted intrusions.

DHCP traffic uses UDP (User Datagram Protocol) and the ports used for transmitting the messages are 67 and 68. The messages from the client to the server use UDP source port 68 and UDP destination port 67. No matter the sender and the receiver, the client will always use UDP port 68 for receiving and sending messages and the server will use UDP port 67 for the same activities.

The messages exchanged between client and server in DHCP communication cover the configuration process and include “notes” from client to server and back.