What is Dynamic Host Configuration Protocol?

By Daniel Imbellino
Updated: Feb 28, 2013

Dynamic Host Configuration Protocol (DHCP) is a network configuration protocol used to allocate, assign, and manage network connections from various nodes (computers, etc) on your internal network. When you connect to the internet, your network interface card, and operating system need several pieces of information in order to establish this connection. This needed information includes an IP address (logical address), subnet mask (identifies the type of network to which a PC, etc belongs), default gateway (the device connecting you to the internet itself, Usually a router), and a DNS (Domain Name System ) server. Without these four pieces of information, you would not be able to establish a connection to the internet from your client PC, etc.

DHCP does the hard work of providing information, establishing, and managing network connections for us. To establish a connection with your router from your wireless PC, your PC first broadcasts a DHCP Discover packet, which is then received by the DHCP server (usually your router). The DHCP server then sends back to the client PC a DHCP Offer packet, in which the client PC responds back with a DHCP request packet. Finally the DHCP server sends back an acknowledgement packet and the client PC receives and IP address, default gateway, DNS server address, and subnet mask.

DHCP provides dynamic IP addressing to internal networks as well as auto configuration of client systems on the network. The client PC receives a lease for an IP address that is provided by the DHCP server. The lease time for a specified IP address to client system can be changed through router settings. Some routers will be default assign a different IP address to client systems every time that client system connects to the network, while as other routers may assign the same (static) IP address to the client systems each time they connect.

Without DHCP we would have to manually configure our network interface cards with an IP address, default gateway, subnet mask, and DNS server address. You can change your network settings such as these directly in windows 7 by clicking start, control panel, network & internet, network & sharing center, change adapter settings, and then right clicking the NIC in question, and selecting properties. Then select “Internet Protocol Versions 4 or 6” from the menu and click configure. windows command prompt

What Happens If My PC Can’t establish a connection with a DHCP server?

If you are using a windows based PC and you can’t establish a connection with a DHCP server, Windows operating systems will automatically assign your PC with an “Automatic Private IP Address”. APIPA addresses always start with 169.254, and these addresses cannot communicate across the open internet. If you click start, type cmd in the search box, and at the command prompt type “ipconfig /all”, without the quotes, you can see your current general network configuration.

Notice with our example below, you can see the assigning of an IPv4 address to our client station, as well as its default gateway, DHCP server, and DNS server, which all addresses are the same since our routers translate our private IP addresses to one public IP address (usually assigned to our actual modem. If you were unable to make a connection to your network (router), you would see an IP address consisting of 169.254 under the IPv4 Address.

example in command prompt one example in command prompt two