Friday , 24 May 2019
Breaking News

Linux PXE boot process-2

Posts in this series
  1. Linux PXE boot process-1
  2. Linux PXE boot process-2

Linux PXE boot process-(Part-2)

PXE boot server components
– DHCP Server    #assign ip address and redirect to tftp Server
– tftp Server       #download boot loaders and configuration file
– syslinux           #provides stage1 boot loader pxelinux.0, which  is installed in boot  server, independent of the OS to be provisioned

The PXE boot process
1. NIC requests DHCP information (DHCP DHCPDISCOVER to port 67/UDP)
2. DHCP server provides bootloader name and IP of tftp server

#relevant DHCP config

nextsever “172.16.1.10”; filename “pxelinux.0”;

3. NIC uses tftp to fetch bootloader into RAM(tftp tftp-server -c get pxelinux.0)
4. BIOS executes bootloader
5. Bootloader uses tftp to find and retrieve configuration file in following order:
[5.1] MAC address using hex and dashes, prefaced with ARP type code
[5.2] IP address expressed in hex

#Convert decimal to hex by gethostip command
$gethostip 192.0.2.91
192.0.2.91 192.0.2.91 C000025B
[5.3]Strips one digit of hex IP at a time from the right-hand side until file is found
[5.4]Last attempt is default

As an example, if the boot file name is /tftpboot/pxelinux.0, the Ethernet MAC address is 88:99:AA:BB:CC:DD and the IP  address 192.0.2.91, it will try:
/tftpboot/pxelinux.cfg/01-88-99-aa-bb-cc-dd
/tftpboot/pxelinux.cfg/C000025B

/tftpboot/pxelinux.cfg/C000025
... 
/tftpboot/pxelinux.cfg/C
/tftpboot/pxelinux.cfg/default

6. Bootloader load kernel: vmlinuz and initrd.img defined in the configuration file retrieved.

Check Also

Red Hat Enterprise Linux 7 Hardening Checklist

Red Hat Enterprise Linux 7 Hardening Checklist  Preparation and Physical Security 1 If machine is …

Leave a Reply