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MPC20/20L/21/21C MPC20WOL/21WOL / Boot from LAN – PXE & WOL (Wake On LAN)
PXE Boot and PXE Protocol
PXE is defined on a foundation of industry-standard Internet protocols and services that are widely deployed in the
industry, namely TCP/IP, DHCP, and TFTP. These standardize the
form of the interactions between clients and servers.
To ensure that the meaning of the client-server interaction is standardized as well, certain vendor option fields in
DHCP protocol are used, which are allowed by the DHCP standard. The operations of standard DHCP and/or BOOTP
servers (that serve up IP addresses and/or NBPs) will not be disrupted by the use of the extended protocol. Clients
and servers that are aware of these extensions will recognize and use this information, and those that do not
recognize the extensions will ignore them.
In brief, the PXE protocol operates as follows. The client initiates the protocol by broadcasting a DHCPDISCOVER
containing an extension that identifies the request as coming from a client that implements the PXE protocol.
Assuming that a DHCP server or a Proxy DHCP server implementing this extended protocol is available, after several
intermediate steps, the server sends the client a list of appropriate Boot Servers. The client then discovers a Boot
Server of the type selected and receives the name of an executable file on the chosen Boot Server. The client uses TFTP
to download the executable from the Boot Server. Finally, the client initiates execution of the downloaded image. At
this point, the client’s state must meet certain requirements that provide a predictable execution environment for the
image. Important aspects of this environment include the availability of certain areas of the client's main memory,
and the availability of basic network I/O services.
Deployment of servers
On the server end of the client-server interaction there must be available services that are responsible for providing
redirection of the client to an appropriate Boot Server. These redirection services may be deployed in two ways:
1. Combined standard DHCP and redirection services.
The DHCP servers that are supplying IP addresses to clients are modified to become, or are replaced by servers
that serve up IP addresses for all clients and redirect PXE-enabled clients to Boot Servers as requested.
2. Separate standard DHCP and redirection services.
PXE redirection servers (Proxy DHCP servers) are added to the existing network environment. They respond
only to PXE-enabled clients, and provide only redirection to Boot Servers. Each PXE Boot Server must have one
or more executables appropriate to the clients that it serves.
Preboot Execution Environment (PXE) Specification 11
Version 2.1 September 20, 1999
Copyright © 1998, 1999 Intel Corporation. All rights reserved.
This diagram illustrates the relationship between the NBP (the remote boot program) and the PXE APIs.