Understanding NetBoot

Upon further dissection, NetBoot is a combination of several different protocols, working in concert to facilitate the remote booting of an operating system over the network. The services required to provide NetBoot include Dynamic Host Configuration Protocol (DHCP) to provide initial IP addressing information, Boot Service Discovery Protocol (BSDP) to advertise the location of the NetBoot server, Trivial File Transfer Protocol (TFTP) to deliver the initial boot files, and either Network File System (NFS) or Web services via HyperText Transfer Protocol (HTTP) to mount the system boot image.

On the client side, the Open Firmware instructions built into the hardware of every modern Apple computer facilitate the NetBoot startup process. While Open Firmware is being replaced by the Extensible Firmware Interface (EFI) on the newer Intel-based Macs, the NetBoot process itself remains primarily the same.

One type of boot image, dubbed an install image, can be used to facilitate rapid mass deployment across your network. After you start up a computer, the install image can then automatically install onto the local volume all the software required for your system build. Another potential use for NetBoot is to create an image that contains all your favorite system maintenance and repair utilities.

You can configure the ultimate administrator's toolkit, which is available to any computer on your network at any timewithout having to carry a single CD or FireWire disk! Each server can host 25 different images, and you can use as many NetBoot servers as you need on your network. NetBoot servers will even automatically load-balance traffic for high-demand images if the same image is on multiple servers.

What's an Image ID?

The Image ID is a unique number of your choosing that client computers use to identify the boot image. If a boot image will be available from only one server, chose an ID number between 1 and 4095. However, if a boot image will be available from several servers, choose a number between 4096 and 65535.

If a client computer finds an image with the same ID on multiple servers, the client will assume they're identical image files and boot off the first image it receives from any of the servers containing that image. This has the effect of doing rudimentary load balancing between multiple NetBoot servers. The Image ID is entered into the Image Index field of the System Image Utility when creating a new boot image.