Getting *nix to Netboot Macs

Intro

So, you wanted to move your netbooting off of a OS X box, and onto a box running ISC DHCP, for one reason or another. Well, you stumbled on the right page! This should help you get booting from a ISC DHCP based DHCP server working with just a little bit of work.

What is this all about?

For any number of reasons, you may want to move the server(s) handling your Mac netboot to ISC's DHCP Server. I will not go into any of the reasons, as it does not matter for this material, and is highly dependent on your situation. The code below should allow you to enable netbooting for your Macs in such a manor that allows you to serve multiple images, that can be selected in firmware at the alt/option-boot menu.

What does this page assume?

• You already have a working ISC DHCP Server setup, and want to expand it for serving up netboot images via BSDP.
• You already have a server that will hold the netboots (either the same server as DHCP, or another, does not matter).

My Testing Environment

• Internet Systems Consortium DHCP Server 4.2.3-P2 Gentoo-r0
• (work issued) Apple MacBookPro6,2, Purchased Fall 2010

The Code

• This presents two images to the Alt/Option Boot menu:
  • ID: 137, Name: DOE-Image (Also our default image)
  • ID: 138, Name: DSR-NB01012012-05122012
• Sets ID 137 to be the Default Image for only holding down N at boot
• Placed between global options and your subnet definitions, this is then enabled for all subnets (Will explore narrowing this down shortly)

class "Apple-Intel-Netboot" {
	# Limit this class to only Intel Apple machines
	match if substring (option vendor-class-identifier, 0, 14) = "AAPLBSDPC/i386";
	option dhcp-parameter-request-list 1,3,17,43,60; # Send these options to the client (possibly forcing it, if the client didn't request it)
							# From: http://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xml
							# 1 - Subnet Mask
							# 3 - Router
							# 17 - Root Path
							# 43 - Vendor Specific
							# 60 - Class ID

	if (option dhcp-message-type = 8) {
		# on DHCPInform Messages, Us/Our (Server), Them (Client)
		option vendor-class-identifier "AAPLBSDPC"; # Let Them know we're responding with Apple BSDP Information
		if (substring(option vendor-encapsulated-options, 0, 3) = 01:01:01) {
			log(info, "BSDP_LIST");
			# BSDP List
			# Let Them know this is the let, what server, the server's priority, what Our default image is, and provide the image list
			option vendor-encapsulated-options
				01:01:01:			# Start BSDP Inform/List Option 1 (01:), Length 1 (01:), Message Type List(1) (01:)
				03:04:				# BSDP option code 3 (length 04) -- Server Identifier
					0A:00:03:02:		# Server IP (10.0.3.2), Dec->Hex
				04:02:				# BSDP option code 4 (length 02) -- Server Priority
					80:00:			# Priority (32768) Dec->Hex
				07:04:				# BSDP option code 7 (length 04) -- Default Image ID
					81:00:00:89:		#     Image ID - (137) Dec->Hex
								# This is what is picked as Default when you only hold down N on the client
								#
								# 81 breaks into: 0 or 8 for Non-Install (NetBoot) set or Install (NetInstal) set,
								# Most, including DeployStudio default to NetInstall set.
								# Then 0 for Mac OS 9, 1 for Mac OS X (Client)
								# 2 for OS X Server, and 3 for Hardware Diagnostics
								# 4- through 127 (x4:00-xf:ff) reversed for future use
								# And the last two are for the Image ID (Dec->Hex)
								# IDs 1-4095 (00:01-0F:FF) are for Server-Specific Images (You will probably want an ID in this range)
								# IDs 4096-65535 (10:00-FF:FF) Are "Globally-Unique", Multiple servers can present this same ID
								# and the client will only see one image, and pick a random(?) server to talk to.
								#
				09:				# BSDP option code 9 -- Boot image list
					2A:			# Length - =5*<numofimages>+<sumofallimagenames>, eg =5*2+(23+9), =10+32, =42, Dec->Hex =2A
								# This only appears once in the pacakge, no matter how many images you have below
						81:00:00:89:	# Image ID (137) -- dec->hex, see above (Default Image ID) for how to forumlate the full ID
							09:44:6f:45:2d:49:6d:61:67:65:	# Length(09):Name 'DoE-Image' ascii->hex
						81:00:00:8A:				# Image ID -- 138
							17:44:53:52:2d:4e:42:30:31:30:31:32:30:31:32:2d:30:35:31:32:32:30:31:32; # Length(Hex:17,Dec:23):Name 
																# Name: DSR-NB01012012-05122012
		} elsif (substring(option vendor-encapsulated-options, 0, 3) = 01:01:02) {
			log(info, "BSDP_SELECT");
			# BSDP Select, This is the client selecting which image they want to boot from
			# Here we basically do if statements to catch what image is referenced
			# Since we MIGHT be clustered, Check to see if we're the server being asked, this is BSDP Option 3 (Length 04)
			if (substring(option vendor-encapsulated-options, 9, 4) = 0A:00:03:02) { # Match to IP: 10.0.3.2, same as above. You'll want to change this
				log(info, "BSDP_SELECT-Responding, Client is talking to us."); # Log we're being talked to
				if (substring(option vendor-encapsulated-options, 15, 4) = 81:00:00:89) { # Catch Image ID 81:00:00:89
					log(info, "BSDP_SELECT-Image: 137:DOE-Image"); # This isn't _needed_, but is nice for debugging/knowing
					# Insert stuff needed to boot here
					filename "/osx/i386/booter";
					next-server 10.25.64.32;
					option root-path = "http://10.25.64.32/build.sparseimage";
				} elsif (substring(option vendor-encapsulated-options, 15, 4) = 81:00:00:8A) { # Catch Image ID 81:00:00:8A
					log(info, "BSDP_SELECT-Image: DSR-NB01012012-05122012");
					# Insert stuff here needed for boot
					# This example is from the FOG Project: http://fogproject.org/wiki/index.php?title=How_to_get_Macintosh%27s_Netboot_working_with_your_FOG_server
					filename "macnbi-i386/booter";
					#Replace 192.168.1.1 with the server's actual IP address.
					#Need clarification if NetRestore works for both Intel and PowerPC
					#For DeployStudio, either copy DeployStudioRuntime.sparseimage to /nbi, or use nfs share to connect to deploy studio server
					#option root-path "nfs:<deploystudio_ip>:/Volumes/<volume_label>/Library/NetBoot/NetBootSP0:<runtime_folder>/DeployStudioRuntime.sparseimage";
      					#option root-path "nfs:192.168.1.1:/nbi:DeployStudioRuntime.sparseimage";
					option root-path "nfs:192.168.1.1:/nbi:NetInstall-Restore.dmg";
					next-server 192.168.1.1;
				} else {
					log(info,"BSDP_SELECT-ERROR: Client responded with an image we don't have a match for! -- (Image added to list, but not in select catch?)");
				} 	# End Image Selection Response
			} else {
				log(info,"BSDP_SELECT-Ignoring, Client is talking to another server--We're not worthy!"); # Log that we are not worthy of the client's time
			} 		# End Server Check
		} 			# End BSDP Options Check
	} 				# End DHCPInform Messages
} 					# End Class

Caveats

• This does not present the netboot sets to the Startup Disk System Preferences Pane
  • The SD Pref Pane does send out the proper BSDP List packet, however since there is already a DHCP Client listening on the default ports, the SD Pref Pane needs the response sent to another port (which is included in the packet), however I have not yet found a way for ISC DHCP to send to this other port when specified. When it gets the List packet, it responds, but to the DHCP Client, not the Pref Pane, hence it doesn't populate.
• Would be enabled on all subnets handled by this DHCP server
• Have not tested it working across DHCP-Relays or VLANs/IP-Helpers yet, however there should be nothing preventing it from working
• All Netboot name lengths (plus 5bit overhead) combined need to be less then 255 characters (Reference Line 40 above), but you could have as many fit into that. I still want to test if you've hit that limit, if we can send another :09: list entry to include more entries (Say for very descriptive names...)
• While this does have a catch for use in redundant/load balancing netboot servers, I haven't tested this yet. However, I don't see this working "As Designed" (or as a full replacement for Apple's dedicated BSDP Service). My thinking is explained next.
• Any functionality that relies on the BSDP Server remembering a previously picked image will 'fail' back to the default.
  • Apple's BSDP Server implements functionality that it will remember the last image that a client selected for boot. Along the same lines, there is also functionality built into it that will reduce the servers preference as it becomes loaded with clients, so then new clients go to other servers. I haven't yet tried to introduce either of these into ISC's DHCP server, however I don't see it being implemented easily.
  • I say 'fail', as it doesn't fail, but the server only knows to hand over the default.
• This will most likely not work with Diskless NetBoot Sets (or "Thin Client" sets), where the server holds a temp location for the client to write files back to
  • (Think booting a SIU Image, like one created by JAMF Here). This involves some Remapping and other funky stuff way beyond just setting up DHCP to handle netboots.

Resources Used to Complete this

• I basically took Bennett Perkin's work, whose work is based on others, and expanded upon it.
• Used EasyCalculation.com for converting Dec->Hex, and Hex->Dec to verify (Image IDs and Lengths)
• Used Dolcevie.com to convert ASCII/Strings to Hex (Image Names)
• I originally got netbooting to work (without multiple images), using an article on AFP548
• Also peaked at FOG Project's recommendations for getting Mac to Netboot
• Verified DHCP Parameters with IANAs List
• Also read Apple's BDSP Documentation about 20 different times

Fin

• Once OSXDeployment.com is out of Read-Only Maintenance mode, I will be posting this information there too (as it's more central for this kind of information). I will be keeping it here too, as my own reference. This site has been rolled into AFP548.
• I have learned more about BSDP then I ever wanted to know :)
• I am available on IRC if you have any questions or comments; irc.freenode.net, channel ##OSX-Server. My Nickname is Sedorox.