BOOTP and DHCP


The Bootstrap Protocol (BOOTP), defined in RFC 951, is the predecessor of DHCP and shares some operational characteristics. BOOTP is a way to download address and boot configurations for diskless workstations. A diskless workstation does not have a hard drive or an operating system. For example, many automated cash register systems at your local super market are examples of diskless workstations. Both DHCP and BOOTP are client/server based and use UDP ports 67 and 68. Those ports are still known as BOOTP ports.

DHCP and BOOTP have two components, as shown in the figure. The server is a host with a static IP address that allocates, distributes, and manages IP and configuration data assignments. Each allocation (IP and configuration data) is stored on the server in a data set called a binding. The client is any device using DHCP as a method for obtaining IP addressing or supporting configuration information.

To understand the functional differences between BOOTP and DHCP, consider the four basic IP parameters needed to join a network:

IP address
Gateway address
Subnet mask
DNS server address
There are three primary differences between DHCP and BOOTP:
The main difference is that BOOTP was designed for manual pre-configuration of the host information in a server database, while DHCP allows for dynamic allocation of network addresses and configurations to newly attached hosts. When a BOOTP client requests an IP address, the BOOTP server searches a predefined table for an entry that matches the MAC address for the client. If an entry exists, the corresponding IP address for that entry is returned to the client. This means that the binding between the MAC address and the IP address must have already been configured in the BOOTP server.
DHCP allows for recovery and reallocation of network addresses through a leasing mechanism. Specifically, DHCP defines mechanisms through which clients can be assigned an IP address for a finite lease period. This lease period allows for reassignment of the IP address to another client later, or for the client to get another assignment if the client moves to another subnet. Clients may also renew leases and keep the same IP address. BOOTP does not use leases. Its clients have reserved IP address which cannot be assigned to any other host.
BOOTP provides a limited amount of information to a host. DHCP provides additional IP configuration parameters, such as WINS and domain name.

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