Hitchhiker's Guide to Openbsd

6.10 - How do I boot using PXE? (i386, amd64)
The Preboot Execution Environment, or PXE, is a way to boot a computer from the network, rather than 
from a hard disk, a floppy or a CD-ROM. The technology was originally developed by Intel, but is 
supported by most major network card and computer manufacturers now. Note that there are several 
different network boot protocols, PXE is relatively recent. Traditionally, PXE booting is done using 
ROMs on the NIC or mainboard of the system, but boot floppies are available from various sources that 
will permit PXE booting, as well. Many ROMs on older NICs support network booting but do NOT 
support PXE; OpenBSD/i386 or amd64 cannot currently be booted across the network by these. 
How does PXE booting work?
First, it is wise to understand how 
OpenBSD boots
on i386 and amd64 platforms. Upon starting the boot 
process, the PXE-capable NIC broadcasts a DHCP request over the network. The DHCP server will 
assign the adapter an IP address, and gives it the name of a file to be retrieved from a 
tftp(1)
server and 
executed. This file then conducts the rest of the boot process. For OpenBSD, the file is 
pxeboot
, which 
takes the place of the standard 
boot(8)
 file. pxeboot(8) is then able to load and execute a kernel (such as 
bsd
or 
bsd.rd
) from the same tftp(1) server. 
How do I do it?
The first and obvious step is you must have a PXE-boot capable computer or network adapter. Some 
documentation will indicate all modern NICs and computers are PXE capable, but this is clearly not true 
-- many low cost systems do not include PXE ROMs or use an older network boot protocol. You also 
need a properly configured 
DHCP
and TFTP server. 
Assuming an OpenBSD machine is the source of the boot files (this is NOT required), your DHCP 
server 
dhcpd.conf
file will need to have the following line: 
filename "pxeboot";
to have the DHCP server offer that file to the booting workstation. For example: 
shared-network LOCAL-NET {
option domain-name "example.com";
option domain-name-servers 192.168.1.3, 192.168.1.5;
subnet 192.168.1.0 netmask 255.255.255.0 {
option routers 192.168.1.1;