====== UEFI HTTP chainloading ======

Version 2.5 of the [[http://www.uefi.org|UEFI]] specification introduces the UEFI HTTP Boot feature.  You can use the basic UEFI HTTP Boot client to chainload iPXE from an HTTP server, eliminating the need for a separate TFTP server in your boot infrastructure.

The simple UEFI HTTP Boot client will download and boot iPXE.  You can then use any of iPXE's more advanced features such as [[:crypto|HTTPS]], Digest authentication, [[:cmd:param|POST requests]], [[:scripting|scripts]], [[:cmd:choose|menus]], customisable [[:crypto|code signing]] etc. to download and boot your operating system.

UEFI HTTP chainloading provides a way to load iPXE on systems which do not have iPXE present as part of the UEFI firmware.  If your system already provides iPXE as part of the UEFI firmware, then you do not need to use UEFI HTTP chainloading.

===== Configuring the DHCP server =====

{{ :clipart:chain.jpeg?200x120|A chain}}

You must configure your DHCP server to check for a UEFI HTTP Boot client, and to provide the string ''HTTPClient'' as the vendor class identifier, and an HTTP URI as the boot filename.  If you are using [[:howto:dhcpd|ISC dhcpd]] then you need to edit ''/etc/dhcpd.conf'' to contain

    if option client-architecture = encode-int ( 16, 16 ) {
       option vendor-class-identifier "HTTPClient";
       filename "http://my.web.server/ipxe.efi";
    } else {
       filename "http://my.web.server/script.ipxe";
    }

where **my.web.server** is the DNS name (or IP address) of your web server.
    
===== Configuring the web server =====

Place your iPXE binary (e.g. [[http://boot.ipxe.org/ipxe.efi|ipxe.efi]]) on your web server, along with an iPXE [[:scripting|script]] containing the commands needed to boot your operating system.  For example, to boot a system comprising a Linux kernel and initial ramdisk, your script could contain

    #!ipxe
    kernel http://my.web.server/boot/vmlinuz initrd=initrd.img
    initrd http://my.web.server/boot/initrd.img
    boot

===== Booting =====

Boot your UEFI system and select UEFI HTTP Boot.  You should see it download ''ipxe.efi'' via HTTP and start running iPXE:

    Booting from EFI Network
    Station IP address is 192.168.0.10
    URI: http://squirrel/images/ipxe.efi
    
    iPXE initialising devices...ok
    iPXE 1.0.0+ (33d4b) -- Open Source Network Boot Firmware -- http://ipxe.org
    Features: DNS HTTP TFTP EFI Menu
    
    net0: 52:54:00:12:34:56 using 82540em on PCI00:03.0 (Ethernet) [open]
      [Link:up, TX:0 TXE:0 RX:0 RXE:0]
    Configuring (net0 52:54:00:12:34:56)... ok

Congratulations on successfully using UEFI HTTP chainloading!

{{ :clipart:smile.png?200x200 |Success}} 

===== Advanced topics =====

==== Building OVMF ====

You can build an OVMF image (for virtual machines such as qemu and kvm) which supports UEFI HTTP Boot.  You will need to edit the build description file ''OvmfPkg/OvmfPkgX64.dsc'' to enable the option

    DEFINE HTTP_BOOT_ENABLE        = TRUE

For OVMF (or any other firmware built from upstream EDK2), the UEFI HTTP Boot option will show up as **EFI Network 1** within the boot selection menu.