by Rosemarie Makhmaltchi

Created on: January 13, 2007   Last Updated: April 19, 2007

DHCP and DNS are integral parts of most networks, especially the large ones. If you have ever accessed the Internet, you have used both of them. This short article briefly describes the history, functions, and features of these two indispensable services.

DHCP
Dynamic Host Configuration Protocol (DHCP) is a protocol defined by the Internet Engineering Task Force (IETF) RFCs 2131 and 2132. It communicates configuration data to hosts on a TCP/IP network, dramatically reducing the amount of administrative work involved in maintaining these networks. It is based on the Bootstrap Protocol (BOOTP) of the early networking days, but unlike BOOTP, it can dynamically assign configuration parameters such as IP addresses and subnet masks to clients using TCP/IP. DHCP supports three ways to assign IP addresses: Automatic Allocation, Dynamic Allocation, and Manual Allocation. Automatic allocation is achieved when DHCP permanently assigns an IP address to a client. This is also referred to as an address Reservation; the IP address is permanently leased to the client. This ensures that mail and file servers that are accessed by their IP addresses can be easily reached by users. These types of servers should not be assigned addresses through Dynamic allocation. Dynamic allocation involves the temporary leasing of IP addresses to TCP/IP clients. When said lease expires, the client receives a new (and often different) IP address. DHCP leases can be set to last from one minute to 999 days. By default, it is set to eight days. Dynamic allocation requires the least amount of administrative interference. With Manual allocation, the client's IP address is set by the network administrator, so it is not allocated by the DHCP server.

DNS
The Domain Name System (DNS) was introduced in 1984 on the ARPANET the first large-scale computer network. Its purpose is to resolve host names to IP addresses, thus eliminating the need for users to remember binary addresses for each server or printer they desire to connect to. DNS was created as a replacement for the hosts.txt file used on the early ARPANET. Hosts.txt was a database of all host names and their corresponding IP addresses on the network. It was updated each time a host left or joined the network, and users had to periodically download the file in order to get the most recent version. This inefficient method of address resolution was unsuitable for large networks. DNS resolves IP addresses to host names, and also allows this data to be distributed across several servers, thus distributing the burden of this service. It is also very scalable, and able to handle name resolution even on large, volatile networks, such as the Internet. DNS works in conjunction with DHCP, so it always resolves the most current IP address to any host name on the network (its database is updated dynamically). Another fantastic feature of DNS is that it is hierarchical, allowing for levels upon levels of networks and subnets. Using hierarchical structuring, computer networks can reflect the structure of their organizations, and thus become easier to navigate and manage.

SOURCES

Alexander and R. Droms. "DHCP Options and BOOTP Vendor Extensions" (rfc 2132). Rfc-editor.org. March 1997. Network Working Group. 8 Sept. 2005. <>.

Bott, Greg. Implementing, Managing, and Maintaining a Microsoft Windows Server 2003 Network Infrastructure. Redmond, WA: Microsoft Press, 2004.

Droms, R. "Dynamic Host Configuration Protocol" (rfc 2131). Rfc-editor.org. March 1997. Network Working Group. 8 Sept 2005. <>.

Klensin, J. "Role of the Domain Name System (DNS)" (rfc 3467). Rfc-editor.org. February 2003. Network Working Group. 8 Sept. 2005. <>.

Learn more about this author, Rosemarie Makhmaltchi.
Click here to send this author comments or questions.