Abstract:
A chained bootstrap that is identified on a Boot Image Negotiation Layer (BINL) server and which is specified as the default bootstrap for the remote booting of client machines without regard to what client OS will finally be booted, is provided. The default bootstrap is downloaded as the initial bootstrap when the client sends the remote boot request to the TFTP boot server identified by the BINL server. This bootstrap then acquires a configuration file for the client from the TFTP server and determines the specific OS and associated bootstrap to download to the client. The chained bootstrap then relocates itself in memory on the client so that the actual client OS bootstrap can load and execute properly. The chained bootstrap then requests the actual client bootstrap from the TFTP server to continue the boot of the OS.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to client computers that are bootable over a network and, in particular, to the remote booting of multiple operating systems by those client computers. 
     2. Description of Related Art 
     Some current personal computer motherboards, network adapters, and boot diskettes include support for the preboot execution environment (PXE) to download an operating system (OS) from the network. PXE relies on extensions to the bootstrap protocol (BOOTP) and dynamic host configuration protocol (DHCP) to identify the source of the OS. PXE uses the trivial file transfer protocol (TFTP) to download the OS. PXE also requires the services of a DHCP server, a PXE proxy server, a boot image negotiation layer (BINL) server and a TFTP server. 
     BOOTP is a protocol that operates on networks that can also operate the transmission control protocol/Internet protocol (TCP/IP). BOOTP was developed to be used by a diskless workstation or network computer (NC) to obtain its own IP address, the IP address of a boot server, and the name of the file on that boot server that the client could request to start the download of its OS. Upon startup, the client station sends out a BOOTP request to the BOOTP server, which returns the required information. The BOOTP request and response use an IP broadcast function that can send messages before a specific IP address is known. BOOTP requires that an IP address be manually pre-assigned to each client when the BOOTP server is configured. Only one OS file name can be entered when the BOOTP server is configured, so all clients must receive the same OS. The software that transfers the OS files to the client must run on the same physical server as the BOOTP server software that supplies the IP addresses and OS file name information to the client. 
     DHCP is a protocol based on the BOOTP protocol that was developed to offer improved flexibility for the configuration of computers attached to a network. DHCP servers operate software that automatically assigns IP addresses to client stations logging onto a TCP/IP network. DHCP eliminates having to manually assign permanent IP addresses to clients. 
     PXE extensions added to the DHCP protocol enables DHCP to redirect client stations that need to be booted to a BINL server to obtain boot information, permitting client configuration and client boot to be administered separately. In fact, two different servers can respond to the initial DHCP request from a client. A “standard” DHCP server offers the client an IP address. A proxy DHCP, also called a “PXE proxy” server, redirects the client to a BINL server. 
     The BINL server references the address of a TFTP boot server and the name of the file to request from the TFTP boot server that contains a network bootstrap program (NBP). The client communicates with the BINL server using DHCP-formatted messages. 
     PXE enables a client network computer that lacks a native operating system to locate and identify an NBP through a network attachment using DHCP and its extensions. PXE also enables the client network computer to acquire the NBP from the TFTP server through that network attachment. PXE also provides a means for running the NBP on the client to continue the network acquisition of additional software required to make the client capable of performing the more complex and useful tasks assigned to it by an enterprise. 
     A facilitating property of DHCP is that the client does not initially need the address of any other computer. The client performs a DHCP broadcast to discover any DHCP server or PXE proxy server that can recognize that the client is PXE-capable. The DHCP server or PXE proxy server sends a DHCP offer to the client, which contains the address of the BINL server. The client then sends a BINL request to the BINL server. The BINL server returns a BINL reply that references the address of a TFTP boot server and the name of a file from which the client may obtain the NBP. The client then obtains the NBP and all necessary software from the boot server via TFTP. 
     Current approaches to selecting the operating system to boot on a target client have a dependency on the BINL server which is delivered by multiple vendors, such as Intel, IBM and Microsoft, with different implementations and behaviors on each platform. When attempting to manage the remote boot of multiple operating systems there is the problem of how to seamlessly switch bootstraps that are specific to each operating system without having to write a lot of unique code per BINL server per platform per vendor to concurrently switch the bootstrap file name that is referenced in the BINL server&#39;s configuration. In addition, several of these BINL servers have to be stopped and restarted after every configuration change. This is an expensive process, is platform specific, and also affects the production clients which depend on a running BINL server in order to remote boot correctly. 
     Therefore, a method to remote boot multiple operating systems without having to reconfigure the BINL server for each change in a client operating system would be desirable. 
     SUMMARY OF THE INVENTION 
     The present invention provides a chained bootstrap that is identified on a Boot Image Negotiation Layer (BINL) server and which is specified as the default bootstrap for the remote booting of client machines. The default bootstrap is downloaded as the initial bootstrap when the client sends the remote boot request to the TFTP boot server identified by the BINL server. This bootstrap then acquires a configuration file for the client from the TFTP server and determines the specific OS and associated bootstrap to download to the client. The chained bootstrap then relocates itself in memory on the client so that the actual client OS bootstrap can load and execute properly. The chained bootstrap then requests the actual client OS bootstrap from the TFTP server to continue the boot of the OS. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with accompanying drawings, wherein: 
     FIG. 1 depicts a pictorial representation of a network of data processing systems in which the present invention may be implemented; 
     FIG. 2 depicts a block diagram of a data processing system that may be implemented as a server in accordance with a preferred embodiment of the present invention; 
     FIG. 3 depicts a block diagram illustrating a data processing system in which the present invention may be implemented; and 
     FIG. 4 depicts a flowchart illustrating the operation of a chained bootstrap for the remote booting of multiple operating systems, in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference now to the figures, FIG. 1 depicts a pictorial representation of a network of data processing systems in which the present invention may be implemented. Network data processing system  100  is a network of computers in which the present invention may be implemented. Network data processing system  100  contains a network  102 , which is the medium used to provide communications links between various devices and computers connected together within network data processing system  100 . Network  102  may include connections, such as wire, wireless communication links, or fiber optic cables. 
     In the depicted example, a server  104  is connected to network  102  along with storage unit  106 . In addition, clients  108 ,  110 , and  112  also are connected to network  102 . These clients  108 ,  110 , and  112  may be, for example, personal computers or network computers. In the depicted example, server  104  provides data, such as boot files, operating system images, and applications to clients  108 - 112 . Clients  108 ,  110 , and  112  are clients to server  104 . Network data processing system  100  may include additional servers, clients, and other devices not shown. 
     In the depicted example, network data processing system  100  is the Internet with network  102  representing a worldwide collection of networks and gateways that use the TCP/IP suite of protocols to communicate with one another. At the heart of the Internet is a backbone of high-speed data communication lines between major nodes or host computers, consisting of thousands of commercial, government, educational and other computer systems that route data and messages. Of course, network data processing system  100  also may be implemented as a number of different types of networks, such as for example, an intranet, a local area network (LAN), or a wide area network (WAN). FIG. 1 is intended as an example, and not as an architectural limitation for the present invention. 
     The present invention provides a network environment, which may include DHCP/PXE proxy servers, such as servers  104 ,  105 , and multiple boot servers running BINL and TFTP server software, which may be collocated on servers  104 ,  105  with the DHCP/PXE proxy servers. A client computer, such as one of clients  108 ,  110 ,  112 , includes pre-boot extensions to download operating system information from a boot server. 
     Referring to FIG. 2, a block diagram of a data processing system that may be implemented as a server, such as server  104  in FIG. 1, is depicted in accordance with a preferred embodiment of the present invention. Data processing system  200  may be a symmetric multiprocessor (SMP) system including a plurality of processors  202  and  204  connected to system bus  206 . Alternatively, a single processor system may be employed. Also connected to system bus  206  is memory controller/cache  208 , which provides an interface to local memory  209 . I/O bus bridge  210  is connected to system bus  206  and provides an interface to I/O bus  212 . Memory controller/cache  208  and I/O bus bridge  210  may be integrated as depicted. 
     Peripheral component interconnect (PCI) bus bridge  214  connected to I/O bus  212  provides an interface to PCI local bus  216 . A number of modems may be connected to PCI bus  216 . Typical PCI bus implementations will support four PCI expansion slots or add-in connectors. Communications links to network computers  108 - 112  in FIG. 1 may be provided through modem  218  and network adapter  220  connected to PCI local bus  216  through add-in boards. 
     Additional PCI bus bridges  222  and  224  provide interfaces for additional PCI buses  226  and  228 , from which additional modems or network adapters may be supported. In this manner, data processing system  200  allows connections to multiple network computers. A memory-mapped graphics adapter  230  and hard disk  232  may also be connected to I/O bus  212  as depicted, either directly or indirectly. 
     Those of ordinary skill in the art will appreciate that the hardware depicted in FIG. 2 may vary. For example, other peripheral devices, such as optical disk drives and the like, also may be used in addition to or in place of the hardware depicted. The depicted example is not meant to imply architectural limitations with respect to the present invention. 
     The data processing system depicted in FIG. 2 may be, for example, an IBM RISC/System 6000 system, a product of International Business Machines Corporation in Armonk, N.Y., running the Advanced Interactive Executive (AIX) operating system. 
     With reference now to FIG. 3, a block diagram illustrating a data processing system is depicted in which the present invention may be implemented. Data processing system  300  is an example of a client computer. Data processing system  300  employs a peripheral component interconnect (PCI) local bus architecture. Although the depicted example employs a PCI bus, other bus architectures such as Accelerated Graphics Port (AGP) and Industry Standard Architecture (ISA) may be used. Processor  302  and main memory  304  are connected to PCI local bus  306  through PCI bridge  308 . PCI bridge  308  also may include an integrated memory controller and cache memory for processor  302 . Additional connections to PCI local bus  306  may be made through direct component interconnection or through add-in boards. In the depicted example, local area network (LAN) adapter  310 , SCSI host bus adapter  312 , and expansion bus interface  314  are connected to PCI local bus  306  by direct component connection. In contrast, audio adapter  316 , graphics adapter  318 , and audio/video adapter  319  are connected to PCI local bus  306  by add-in boards inserted into expansion slots. Expansion bus interface  314  provides a connection for a keyboard and mouse adapter  320 , modem  322 , and additional memory  324 . Small computer system interface (SCSI) host bus adapter  312  provides a connection for hard disk drive  326 , tape drive  328 , and CD-ROM drive  330 . Typical PCI local bus implementations will support three or four PCI expansion slots or add-in connectors. 
     An operating system runs on processor  302  and is used to coordinate and provide control of various components within data processing system  300  in FIG.  3 . The operating system may be a commercially available operating system, such as Windows 2000, which is available from Microsoft Corporation. An object oriented programming system such as Java may run in conjunction with the operating system and provide calls to the operating system from Java programs or applications executing on data processing system  300 . “Java” is a trademark of Sun Microsystems, Inc. Instructions for the operating system, the object-oriented operating system, and applications or programs are located on storage devices, such as hard disk drive  326 , and may be loaded into main memory  304  for execution by processor  302 . 
     Those of ordinary skill in the art will appreciate that the hardware in FIG. 3 may vary depending on the implementation. Other internal hardware or peripheral devices, such as flash ROM (or equivalent nonvolatile memory) or optical disk drives and the like, may be used in addition to or in place of the hardware depicted in FIG.  3 . Also, the processes of the present invention may be applied to a multiprocessor data processing system. 
     As another example, data processing system  300  may be a stand-alone system configured to be bootable without relying on some type of network communication interface, whether or not data processing system  300  comprises some type of network communication interface. As a further example, data processing system  300  may be a Personal Digital Assistant (PDA) device, which is configured with ROM and/or flash ROM in order to provide non-volatile memory for storing operating system files and/or user-generated data. 
     The depicted example in FIG.  3  and above-described examples are not meant to imply architectural limitations. For example, data processing system  300  also may be a notebook computer or hand held computer in addition to taking the form of a PDA. Data processing system  300  also may be a kiosk or a Web appliance. 
     With reference now to FIG. 4, a flowchart illustrating the operation of a chained bootstrap for the remote booting of multiple operating systems is depicted in accordance with the present invention. The process begins and sends a DHCP broadcast (step  402 ). Thereafter, the process receives DHCP/PXE proxy offers (step  404 ) and sends a BINL request to a BINL server (step  406 ). Then, the process receives a BINL reply from the BINL server (step  408 ) indicating the IP address of a TFTP server and the name of a file that contains the initial NBP. 
     The process then sends a TFTP request for the initial NBP file (step  410 ) to the TFTP boot server indicated in the BINL reply, and receives the initial NBP file from the boot server (step  412 ). This NBP file is a chained bootstrap, which is specified once as the default bootstrap. This bootstrap is always the first bootstrap loaded on the target client machine. A reference to this bootstrap is the only entry in the BINL server. 
     Next, the chained bootstrap looks for the client&#39;s configuration information file on the TFTP server (step  414 ) to determine which actual OS, and its associated bootstrap, should be downloaded to the target client. The configuration file is written into a client-specific directory (one per MAC address), and contains location information for and name of the target OS bootstrap. This configuration file is managed by a separate system, such as, for example, IBM&#39;s Workspace On-Demand, making it independent of the implementation of BINL servers from different vendors. 
     The chained bootstrap then relocates itself on memory on the client machine (step  416 ) so that the actual client OS bootstrap can be loaded and execute correctly. 
     A TFTP request is then made for the OS-specific second bootstrap file designated in that client-specific configuration file (step  418 ). The OS-specific second bootstrap is loaded to the client (step  420 ) and that bootstrap processes the download of the OS to the client (step  422 ). 
     BINL servers are supposed to provide a mechanism to identify different boot images to a target client. Unfortunately, this solution is BINL vendor-specific. The advantage of the present invention is that the BINL server has to be configured only once. The BINL configuration does not change whenever client OS changes are made for any client, or when new OS&#39;s are added. This allows the default bootstrap to chain itself (interpose itself in front of) the actual client OS bootstrap. This solves both the knowledge problem in configuring the BINL server, the restart problem, and the BINL availability problem mentioned above. 
     It is important to note that while the present invention has been described in the context of a fully functioning data processing system, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in the form of a computer readable medium of instructions and a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media, such as a floppy disk, a hard disk drive, a RAM, CD-ROMs, DVD-ROMs, and transmission-type media, such as digital and analog communications links, wired or wireless communications links using transmission forms, such as, for example, radio frequency and light wave transmissions. The computer readable media may take the form of coded formats that are decoded for actual use in a particular data processing system. 
     The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.