What protocol is used to serve the initial PXE image to a local workstation?

The protocol used to serve the initial PXE (Preboot Execution Environment) image to a local workstation is TFTP (Trivial File Transfer Protocol). TFTP is specifically designed for simplicity and lightweight transfer of files, making it ideal for scenarios such as PXE booting, where minimal overhead is desired.

When a workstation boots up and initiates a PXE request, it communicates with a PXE server using a broadcast to find a server that can provide the necessary boot image. The server responds with the location of the boot image, and TFTP is then utilized to transfer that image to the workstation.

TFTP is preferred in this context due to its ease of implementation in network environments where a simple boot procedure is required, as it does not require authentication and operates over UDP (User Datagram Protocol). This results in faster transmission times and less complexity compared to more robust protocols such as HTTP or FTP.

Using alternatives like HTTP, FTP, or SSH would introduce unnecessary complexity or requirements, such as authentication and added overhead, which are not suited for the quick and efficient transfer required during the early boot process when systems are initially starting up.