What Is The Bootstrap Protocol?

Date First Published: 31st May 2022

Topic: Computer Networking

Subtopic: Internet Protocols

Article Type: Computer Terms & Definitions

Difficulty: Advanced

Difficulty Level: 9/10

CONTENTS

How Does BOOTP Work?

Learn more about what the bootstrap protocol in this article.

Not to be confused with the Bootstrap, an open-source CSS framework used in frontend web development.

The Bootstrap Protocol, often abbreviated to BOOTP is an IP protocol that is used to automatically provide a host with an IP address from a configuration server during its boot up through the bootstrap process. It was defined as RFC 951 in September 1985 with the aim of replacing the Reverse Address Resolution Protocol, defined in RFC 903 in June 1984. Even though the Bootstrap Protocol has mostly been superseded by the Dynamic Host Configuration Protocol which has additional features and flexibility, there are parts of BOOTP that are used to provide functionality to the Dynamic Host Configuration Protocol and DHCP servers also provide the additional functionality.

BOOTP makes use of UDP as the transport protocol, uses port 67 by the DHCP server to receive user requests, and uses port 68 to receive DHCP server responses. The BOOTP server automatically assigns the IP address from a pool of addresses for a certain period of time.

Note:

BOOTP only works on IPv4 networks. It does not support IPv6 networks.

How Does BOOTP Work?

Situation 1: Client and server on the same network.

Originally, a BOOTP client has no IP configuration when it is booted up. Instead, it broadcasts its MAC address to the network as a BOOTP request. Afterwards, the BOOTP server receives the message and replies with the following information:

The client’s IP address, subnet mask, and default gateway address.
The IP address and hostname of the BOOTP server.
The IP address of the server that has the boot image, when the client needs to load their operating system.

Once the client receives this information, it configures and initialises its TCP/IP protocol and then connects to the server where the boot image is located.

Situation 2: Client and server on different networks.

In this situation, the broadcast data packet cannot pass through the router. The data packet is discarded by the router. The issue with the BOOTP request is that the BOOTP request is broadcast.
In order to resolve this issue, a vendor extension is used as an intermediary to act as the relay agent.
The relay agent is configured with the unicast address of the BOOTP server and listens for broadcast messages on port 67.
When it receives this broadcast packet, it sends the message into a unicast datagram and sends the request to a BOOTP server.
The data packet that is carrying a unicast datagram is routed by a router and reaches the BOOTP server.
After receiving the reply, the relay agent sends it to the BOOTP client.