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      Configuring Windows 2000/2003 for Etherboot

      Paul Whittaker (Paul.Whittaker@iname.com)
      Director, Cloud Network Technologies Pty Ltd, Australia

      Last Update: 7 Nov 2004

      Index

      Capabilities and Limitations

      Windows 2000 Server and Windows 2003 Server provide a full featured DHCP server that is quite capable of supporting Etherboot-based diskless/thin clients. This document explains how.

      The DHCP servers provided with Windows 2000/2003 Server and Windows NT 4.0 Server are functionally equivalent except for some back-end storage differences related to Active Directory. There are substantial interface differences, however - the Windows 2000/2003 DHCP manager interface is much improved and far more intuitive. This document therefore applies generally to Windows NT4 also, but the instructions provided here usually cannot be applied literally to the NT4 interface - you must search for the analogous actions under NT4.

      It should also be noted that the version of DHCP server provided with early distributions of NT 4.0 (circa Service Pack 3) is badly broken - you must apply a recent service pack before it will work with Etherboot.

      One thing that Windows DHCP server is not capable of is conditional selection of option values based on vendor class identifiers at run-time. It therefore cannot be used to perform a two-step PXE/Etherboot bootstrap. However, recent versions of Etherboot provide some PXE workarounds (PXE_IMAGE, ZPXE_SUFFIX_STRIP) that ought to make the old two-step method unnecessary. If for some reason you need to use the old method, I am told that Weird Solutions' DHCP Turbo can do it; for a free solution you could use the Internet Software Consortium version 3 DHCP server under Cygwin.

      Unfortunately, some DHCP client implementations cannot properly decode Windows DHCP server responses. In particular, this is a problem with dhclient 2.0, and (last time I checked) the DHCP IP autoconfiguration feature of the Linux kernel.

      As at October 2004, LTSP 3.0 still used dhclient 2.0pl5, which will not work properly with Windows DHCP. Early releases of LTSP 4.0 also used dhclient 2.0pl5, but it now looks as though 4.0 has changed, or will be changing, to dhcpcd 1.3.x. In 2003 I constructed working replacement initrds for both network and pcmcia booting based on ltsp_initrd_kit-3.0.5 using dhcpcd 1.3.22-pl3 instead of dhclient, and submitted them to the LTSP maintainer. For your convenience I have made available a one-off network boot image featuring the alternate initrd. I do not intend to update this.

      Requirements

      In addition to basic environment information (client IP address, subnet mask, default gateway), open source solutions based on Linux and Etherboot typically require that the DHCP server:

      This is not the way DHCP is normally used in the Windows universe. Typically the client provides a hostname in its DHCP request and the server issues it with a temporary IP address, which the server then associates with that hostname for the duration of the lease. This is usually not achievable for diskless clients because the client typically has no permanent storage and therefore no way to store a hostname. Windows DHCP can nevertheless be configured to do what we want.

      Setup

      1. Start the DHCP manager by selecting the DHCP option from the Admin Tools submenu of the Programs menu.
      2. If you have not already done so, authorise your DHCP server. This is necessary to allow your DHCP server to update Active Directory (specifically for dynamic DNS). Select the server hostname and then Authorize from the Actions menu.
      3. If you have not already done so, create a scope (New Scope.. in the Actions menu). You'll need to specify a start and end address, subnet mask, and any exclusions (excluding your server IP address is probably a good idea!). Otherwise, default values should be OK. You can defer configuring scope options and activating the scope for now, we'll deal with that later. If you want to prevent your DHCP server from serving unknown clients, you should exclude the entire IP address range of the scope, such that only clients with reservations can be granted an IP address (see below).
      4. Select the server name and then select Set Predefined Options.. from the right-hand mouse button menu. Click Add.. to add two new entries to DHCP Standard Options set:

        1. Add an option called Etherboot ID with code 128; use data type Byte and check the array box.
        2. Add an option called Etherboot Params with code 129 and data type String.
        3. We now want to preset the contents of the new Etherboot ID option to a special value that cues Etherboot to make use of the 129 and 130 options, if present. To do this, select the Etherboot ID option and click on Edit Array... Select the Hexidecimal radio button and add the hex digits 0x0, 0x68, 0x74, 0x45, 0xe4 (you must include the 0x prefixes) in that order. Do not delete the 0x0 value that is already present. The final display should read "e4 45 74 68 00 00" when done.
      5. Now we need to configure some basic options. Each option may be configured at global, scope, or reservation level; the choice depends upon how many scopes you are serving, which scopes contain non-Etherboot clients, and whether or not the option is scope-specific (ie. subnet-specific), Etherboot-specific, or client-specific. Typically it is convenient to configure most options at scope level. Click on Scope Options and then select Configure Options from the right-hand mouse button menu. Select the checkboxes corresponding to the desired options and set values appropriately. Minimally you will need the following:

        Option NoOption NameExample Value
        6DNS Servers10.0.0.4
        15DNS Domain Namecloud.com.au
        17*Root Path 10.0.0.4:/ltsroot**
        66Boot Server Host Namenimbus
        67Bootfile Name/tftpboot/bootimg**
        128Etherboot IDe4 45 74 68 00 00

        *Only needed if client is NFS-based.
        **Must use UNIX filename conventions (forward slashes). The drive prefix (c: or whatever) is implicit, its value depending upon the configuration of the TFTP/NFS server(s), and must be omitted.
      6. For each Etherboot client you can now add a reservation. Within the scope, click Reservations and then select New Reservation.. from the right-hand mouse button menu. Important fields are IP address and MAC address; the Reservation name is just a label (you can use the hostname if you like), and Both is a safe default for Supported types. Enter the MAC address as a simple 12-digit hexidecimal string (lower case OK) - no colon or period separators. Click Add, and Close when finished adding reservations.
      7. Expand the reservations group, then for each reservation select the reservation and then Configure Options.. from the right-hand mouse button menu. One or both of the following options may be needed:

        Option NoOption NameExample Value
        12Host Namecumulonimbus
        129Etherboot ParamsNIC=ne IO=0x320

      DNS Considerations

      It isn't strictly necessary to have DNS entries for all of your Etherboot client reservations, but it is generally a good idea to do so. At the very least you should ensure that A and PTR records exist for your server name for the interface relevant to your Etherboot scope. Role-specific aliases (CNAMEs) for your server may also be useful.

      If you are using Citrix Metaframe XP / Presentation Server, you should also add a CNAME alias "ica" for the host providing your ICA XML browser service. The Citrix ICA Client uses this as a hardcoded fallback in the absence of explicit browser server information.

      TFTP

      Windows 2000/2003 provides a TFTP server that can be used to serve Etherboot images as part of the Remote Installation Services package. Although it is not intended to be used outside of a RIS context, it is possible to do so with some difficulty.

      Normally it is not possible to install the TFTP server in isolation - you must install the entire RIS service, which will subsequently complain incessantly about being left unconfigured until you feed it the Windows 2000 Professional CDs that it wants. However, Morgan Simonsen (mds at tiscali dot no) and Stefan Kanthak (skanthak at nexgo dot de) have devised ways around this. Morgan's solution is available from http://www.simonsen.bz/Download/TFTPDaemon_v1.1.zip. Stefan has written a tftpd.inf file that you can use to install the TFTP server from the Windows CD - download this file, then simply right click on this file and select Install. Robert Ardill (robert dot ardill at saugov dot sa dot gov dot au) has provided an updated version which works with Windows 2K3.

      To use Windows 2000 TFTP server, you must tweak the registry to tell the server which directory to use as the TFTP root. The value needed is:

      HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Tftpd\parameters\Directory

      If you have not yet configured RIS, some of the rightmost keys in this path will be missing and you will have to create them. The string value is simply a Windows pathname of your choice, eg. C:\Tftpboot or whatever. Having set this, you need only use the Windows Control Panel to configure the TFTP service to start automatically.

      For NT 4.0 you will need to find a third party TFTP server. If you need a server which supports the "tsize" option (eg. for PXELinux), try tftpd32. Otherwise, I recommend TFTP Server 1.2 for NT by Bud Millwood (Millwood Data A.B., Sweden), a shareware product at an entry price of US$40. This is the best well-behaved no-frills NT service I have found so far. This is a defunct product which is no longer widely available, having been superceded by Weird Solutions' TFTP Turbo, so I've made a copy available here. Millwood TFTP Server runs as a service under both Windows NT4 and Windows 2000, and keeps working indefinitely without a license.

      NFS

      There are no good NFS server implementations for Windows platforms. NFS implements traditional UNIX file ownerships and permissions, which don't map well to FAT (which has no notion of permissions) or NTFS (which has more advanced ownership and permission capabilities). Windows also has no notion of a symbolic link or a block/character special file. Consequently the best that one can hope to achieve is a clumsy emulation of a UNIX-like filesystem.

      If your NFS-based diskless client uses the devfs pseudo-filesystem (2.4/2.6), or sets up /dev in a ramdisk via udev (2.6), then you can sidestep the requirement for block/character special files in your NFS root. However, the requirement for symbolic links is not so easy to dodge. A free Microsoft product known as Microsoft Windows Services For UNIX (SFU) includes an NFS server for Windows that supports symbolic links, but I don't know of any Windows NFS servers that support block/character special files.

      If you have a requirement to serve diskless/thin clients from a Windows platform, I urge you to consider a self-booting solution (CDROM or flash disk) or a solution that only requires TFTP (such as DIET-PC, Thinstation or PXES) rather than NFS-based solutions such as LTSP. If you do want to use NFS/LTSP, here's how to do it using Microsoft SFU:

      1. Create a directory to serve as your NFS root directory, eg. c:\ltsroot, and a subdirectory named "etc" within this directory. You must use an NTFS filesystem.
      2. Using a Windows TFTP or FTP client program (e.g. tftp.exe or ftp.exe), transfer the /etc/passwd and /etc/group files from the thin client root filesystem on your development box into the newly created etc directory. If you are using LTSP, you will find these files in /opt/ltsp/i386/etc.
      3. Install Windows Services for UNIX 3.5. SFU provides a wide range of services; the only components of interest to us in this instance are Server for NFS, User Name Mapping and Server for NFS Authentication. If you are using an older version of SFU, beware: it may not work with an installation path that contains spaces (such as C:\Program Files\SFU). For SFU 3.5, you will be asked some up-front questions during the install. You should select Change the default behaviour to case sensitive, and opt for a Local Unix Name Mapping Server using Password and Group Files (unless you also want to install the NIS server, and your thin clients are cabaple of using NIS, in which case NIS is also an acceptable option; in this case, ensure that you add the relevant NIS options to DHCP also). When prompted for the location of the UNIX password and group files, enter the locations of the /etc/passwd and /etc/group files that you transferred earlier (eg. c:\ltsroot\etc\passwd).
      4. After install, select Services for UNIX Administration from the menu. If you are using an old version of SFU which didn't prompt for UNM options during the install, select Server for NFS and then the User Mapping tab and then enter "localhost" in the text box. No extra Server for NFS configuration is required for SFU 3.5.
      5. Select User Name Mapping, and then the Configuration tab. If you have an old version of SFU which didn't prompt for passwd and group file locations during the install, Click the PCNFS radio button and enter these now. Don't be alarmed by the term "PCNFS", it really just means flat files, as opposed to NIS; this wording was corrected in later versions of SFU. Now click Apply (at top right).
      6. Select the Maps tab, and click the Advanced maps radio button if there is one. We must now create advanced maps for both passwd and group. Click on Show User/Group Maps to edit, then click List Windows Users/Groups and List UNIX Users/Groups to expand the lists. You should select Set Primary for each mapping you create. Suggested mappings for LTSP are as follows:

        TypeWindows NameUNIX Name
        passwdYOURDOMAIN/Administratorroot
        passwdYOURDOMAIN/Guestnobody
        passwdYOURDOMAIN/krbtgtbin
        groupYOURDOMAIN/Domain Adminsroot
        groupYOURDOMAIN/Domain Guestsnobody
      7. Click Apply (at top) and close the Services for UNIX Administration snap-in.
      8. To activate NFS sharing, start Windows NT Explorer from the menu, right click on on the NFS root directory you created earlier, select Sharing... and then select the NFS Sharing tab in the window which appears. Use the Permissions button to set sharing to Read-Only for the default group ALL_MACHINES (also enable root access, if you have that as a separate option), and then add an explicit Read-Write permission with root privileges (a single option in SFU 2.0, or a combination of options in 3.5) for the development box from which you will be transferring your thin client root filesystem.
      9. Recursively change onwership of the NFS root directory to the Windows user which you mapped to "root" above. Under NT4, you can't do this - although NTFS will support it, NT4 only gives you the option to "Take Ownership", not to assign it to an arbitrary user, and the implied owner is the Administrators group, not the Administrator user. As a workaround, you will have to recursively assign Full Control privileges to the Everyone group for the time being (copying files from UNIX using tar will correct this later).
      10. Set the following ACLs on the NFS root directory and all subdirectories recursively, replacing any existing ACLs: Full Control for Administrator, and Read and Execute for Administrators, Everyone and ANONYMOUS LOGON (not necessary if it is included in Everyone, which is the case for W2K and earlier, but not XP/W2K3). This is equivalent to root:root rwxr-xr-x. Broadly speaking, SFU equates the NTFS owner and any corresponding ACL with the UNIX "user" permission set, the Everyone ACL with the "other" permission set, and any other ACL with the "group" permission set. In SFU 3.5, ANONYMOUS LOGON is associated with the anonymous NFS user (the UID to which all unresolvable UIDs are mapped). Note that, while historically it was the case, the anonymous NFS user is generally no longer associated with nobody. Due to overuse of this identity by other UNIX services, most UNIX distributions now have a separate identity for this purpose (nfsnobody et al).
      11. There are some additional version-specific considerations:

        SFU 2.0
        Before copying files from your development platform, check and correct permissions on the files you are about to copy. SFU 2.0 doesn't interpret some permission combinations properly, because of the way it maps permissions onto NTFS. In some cases SFU 2.0 uses explicit denials to ensure no access, which has some odd side effects, because the denials take precedence over the allows. For example, you must ensure that all files are readable by group and other, because Administrator is a member of Everyone and Everyone would be denied access. Don't use --x in any column, it isn't understood. Directories must be owner-writable or else you won't be able to read them. In general, it's safest to stick to rwxr-xr-x, rw-r--r-- and r--r--r-- only.

        SFU 3.0
        I have not tested SFU 3.0, and do not know its peculiarities. I expect that its behaviour is similar to that of 3.5.

        SFU 3.5
        SFU 3.5 is more tolerant of odd UNIX permissions, but much stricter in its mapping to Windows identities. You must enable the Allow anonymous access option in the NFS sharing tab (the default -2 values are OK), or else NFS clients will hang when trying to perform any NFS operation. ANONYMOUS LOGON access may need to be explicitly granted as stated above, and you also need to bypass traverse checking for ANONYMOUS LOGON in XP or W2K3 (see the SFU help - Getting Started section, How To subsection). Oddly - from the UNIX perspective - you cannot create files as a UNIX UID that maps to a disabled Windows account; it will get mapped to the anonymous user instead. This means that you will either have to enable the Guest account (typically disabled by default), or create an alternate Windows account for nobody to map to.
      12. On your development platform, mount the NFS root directory from your Windows server (use forward slashes instead of backslashes and omit the drive letter prefix), and transfer files using a method that preserves ownership and permissions (e.g. tar cf - . | tar xCf /mnt -).
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