Bootstrap Protocol: Difference between revisions

Revision as of 08:30, 12 August 2023

Revision as of 21:28, 20 August 2023

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While some parts of BOOTP have been effectively superseded by the [[Dynamic Host Configuration Protocol]] (DHCP), which adds the feature of leases, parts of BOOTP are used to provide service to the DHCP protocol. DHCP servers also provide the legacy BOOTP functionality.

When a network-connected computer [[booting|boots]] up, its IP stack broadcasts BOOTP network messages requesting an IP-address assignment. A BOOTP configuration-server replies to the request by assigning an IP address from a pool of addresses, which is preconfigured by an administrator.

BOOTP is implemented using the [[User Datagram Protocol]] (UDP) for transport protocol, port number 67 is used by the (DHCP) server for receiving client-requests and port number 68 is used by the client for receiving (DHCP) server responses. BOOTP operates only on [[IPv4]] networks.

Historically, BOOTP has also been used for [[Unix-like]] [[diskless workstation]]s to obtain the network ___location of their [[boot image]], in addition to the IP address assignment. Enterprises used it to roll out a pre-configured client (e.g., [[Microsoft Windows|Windows]]) installation to newly installed PCs.

Initially requiring the use of a boot [[floppy disk]] to establish the initial network connection, manufacturers of network cards later embedded the protocol in the [[BIOS]] of the interface cards as well as system boards with on-board network adapters, thus allowing direct network booting.

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When a BOOTP client is started, it has no IP address, so it broadcasts a message containing its MAC address onto the network. This message is called a “BOOTP request”, and it is picked up by the BOOTP server, which replies to the client with the following information that the client needs:

# The client’sclient's IP address, subnet mask, and default gateway address.

# The IP address and host name of the BOOTP server.

# The IP address of the server that has the boot image, which the client needs to load its operating system.

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The Dynamic Host Configuration Protocol (DHCP) was developed as an extension of BOOTP. BOOTP is defined in Request for Comments (RFC) 951 and 1084.

=== Case 2: Client and server on different networks ===

# Problem with the bootp request is that the request is broadcast. A [[IP_addressIP address#Broadcast_addressingBroadcast addressing|broadcast]] [[IP datagram]] cannot pass through any router. The router discards this packet.

# To solve this problem, there is a need for an intermediary (relay).

# One of the host or router can be configured at application layer to operate as relay agent.