Product Documentation

Configuring UEFI pre-boot environments

Sep 28, 2016

XenDesktop supports Unified Extensible Firmware Interface (UEFI) hardware technology on Hyper-V VMs that are managed using SCVMM and streamed using Provisioning Services. This enables customers to:

  • Stream the server operating system at startup time using gigabit network speeds, so users experience faster startups
  • Support TB disks in a virtualized environment

UEFI is a complete replacement for the BIOS and requires a new bootstrap. Two new bootstraps are available: one for 32-bit and one for 64-bit systems.  The introduction of another bootstrap complicates network topologies depending upon how the bootstrap is delivered.

Network topology

Using a PXE server allows for the simplest topology because the PXE protocol works with multiple architectures. The Provisioning Services PXE Server recognizes the architecture flag embedded in the DHCP, then discovers and returns the appropriate bootstrap filename. Both legacy BIOS computers and UEFI computers may therefore be located on the same network segment.

If DHCP option 67 is chosen, there are two topology options:

  • On a single segment, use DHCP reservations to specify the bootstrap filename (option 67) for each and every target device. This is feasible for smaller environments but quickly scales out of hand for enterprise environments.
  • Divide the environment into multiple segments, isolating the legacy devices from the UEFI devices. For each segment, configure a DHCP scope with the appropriate option 67 set.

Configuring bootstraps

The UEFI bootstrap cannot have embedded settings. DHCP options are therefore used to configure the UEFI bootstrap.

DHCP Option 11 – RLP Server

Option 11 allows you to specify multiple IPv4 addresses. Use this option to specify the addresses of the streaming NICs on the Provisioning Services server. You can specify up to 32 addresses. The UEFI bootstrap reads all addresses then uses round-robin to select one address to connect to.


Option 17 takes precedence over option 11.

DHCP Option 17 – Root Path

DHCP Option 66 and Option 67

The Root Path option is typically used with iSCSI to specify the server and virtual disk to start. Provisioning Services uses the following format to specify the server address:


pvs – required identifier

where [] is required and <> is optional.






Option 66 provides the IP address or the hostname of a single DHCP server.


In environments lacking a PXE server, or when booting across VLANs, use DHCP option 67 and 67 (with option 11 or 17).


This method only works when specifying a single bootstrap.

Associating a target device with a bootstrap

Use the BOOTPTAB file to associate a target device with a specific bootstrap. At Provisioning Services 7.7, the following changes have been made to the format of the BOOTPTAB file to support mixed legacy and UEFI environments:

  • The ‘ar’ tag specifies the architecture of the target device’s boot environment. You can make multiple entries for the same MAC address but different architectures. This is for use with hardware that supports both legacy BIOS and UEFI booting.
  • Wildcards are not supported. If an entry for a given MAC address is not found in the BOOTPTAB file, the registry is searched for an appropriate value for the architecture. If neither is found, a default value is used.

The registry is used to provide the default bootstrap file name for a given architecture. The name of the value is the architecture number and the value is a string with the name of the bootstrap file. The following table lists the architectures supported and entries created by the Provisioning Services installer:

HKLM\Software\Citrix\ProvisioningServices\Boot Services\PXE



Bootstrap file name


x86  BIOS



x86 UEFI



x64 UEFI



EBC (for VMware ESX)



The full list of architectures is available from the IETF:

The format of the BOOTPTAB file is:





If the architecture flag is missing, 0 is the default value.


Because of the architectural differences between legacy BIOS systems and UEFI systems, some features of Provisioning Services are not available for UEFI systems:

  • Boot Device Manager (BDM). This tool, which allows you to configure alternative boot methods for Provisioning Services clients using ISO boot or partition offset, is not available for UEFI environments at this release.
  • The Boot menu, which allows users to choose from a selection of available disks and/or versions, is not available. If more than one disk or version exists, selection operates as follows:
    • If a maintenance device boots, it takes (in order of preference) the maintenance version, the highest test version, or a production version, depending on what is available. If updates are applied while the maintenance device is streaming a test or production vdisk, the changes are lost on the next reboot.
    • If multiple vdisks are assigned to a target device, the first vdisk is automatically selected. The user cannot select any other disk.