New PXE build and usage process as of July 2019

Highlights

1. PXE over http, instead of tftp
   1. lpxelinux.0 instead of pxelinux.0
   2. pxelinux.cfg supports urls, ​http:// etc.
   3. find DHCP option to specify URL directly, instead of filename, more reliable bootstrap?
      1. replace filename field with url
2. Support for EFI
3. New PXE image build procedure
   1. Use of mkinitramfs

Client Features

Request list from dhcpdump for i5 NUC, UEFI

  TIME: 2016-04-12 10:48:59.621
    IP: 0.0.0.0 (b8:ae:ed:7d:5f:80) > 255.255.255.255 (ff:ff:ff:ff:ff:ff)
    OP: 1 (BOOTPREQUEST)
 HTYPE: 1 (Ethernet)
  HLEN: 6
  HOPS: 0
   XID: b4683658
  SECS: 12
 FLAGS: 7f80
CIADDR: 0.0.0.0
YIADDR: 0.0.0.0
SIADDR: 0.0.0.0
GIADDR: 0.0.0.0
CHADDR: b8:ae:ed:7d:5f:80:00:00:00:00:00:00:00:00:00:00
 SNAME: .
 FNAME: .
OPTION:  53 (  1) DHCP message type         1 (DHCPDISCOVER)
OPTION:  57 (  2) Maximum DHCP message size 1464
OPTION:  55 ( 35) Parameter Request List      1 (Subnet mask)
					      2 (Time offset)
					      3 (Routers)
					      4 (Time server)
					      5 (Name server)
					      6 (DNS server)
					     12 (Host name)
					     13 (Boot file size)
					     15 (Domainname)
					     17 (Root path)
					     18 (Extensions path)
					     22 (Maximum datagram reassembly size)
					     23 (Default IP TTL)
					     28 (Broadcast address)
					     40 (NIS domain)
					     41 (NIS servers)
					     42 (NTP servers)
					     43 (Vendor specific info)
					     50 (Request IP address)
					     51 (IP address leasetime)
					     54 (Server identifier)
					     58 (T1)
					     59 (T2)
					     60 (Vendor class identifier)
					     66 (TFTP server name)
					     67 (Bootfile name)
					     97 (UUID/GUID)
					    128 (???)
					    129 (???)
					    130 (???)
					    131 (???)
					    132 (???)
					    133 (???)
					    134 (???)
					    135 (???)
					    
OPTION:  97 ( 17) UUID/GUID                 0066ffad1ee719ad .f......
					    849831b8aeed7d5f ..1...}_
					    80               .
OPTION:  94 (  3) Client NDI                010310           ...
OPTION:  93 (  2) Client System             0007             ..
OPTION:  60 ( 32) Vendor class identifier   PXEClient:Arch:00007:UNDI:003016

​ftp://download.intel.com/design/archives/wfm/downloads/pxespec.pdf

DHCPOFFER must specify option 60.