DIGITAL-LOGIC MPC25/L, Техническое руководство пользователя

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DIGITAL-LOGIC AG
MPC25/26 Manual V1.1
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10.1.3.2. 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.