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Improve description of boot process #70

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301f556
Introduce PXE ROM gently
abitrolly Aug 14, 2018
656a2e4
Mention DHCPDISCOVER is iniitial request name
abitrolly Aug 14, 2018
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15 changes: 10 additions & 5 deletions pixiecore/README.booting.md
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# How it works

Pixiecore implements four different, but related protocols in one
binary, which together can take a PXE ROM from nothing to booting
Linux. They are: ProxyDHCP, PXE, TFTP, and HTTP. Let's walk through
the boot process for a PXE ROM.
binary, which together can take a network card to boot system into
Linux. They are: ProxyDHCP, PXE, TFTP, and HTTP. Let's
walk through the network boot process.

![Boot process](https://cdn.rawgit.com/google/netboot/master/pixiecore/bootgraph.svg)

## Step 1: DHCP/ProxyDHCP

Network boot is initiated by PXE ROM firmware that is embedded in
a capable network card.

The first thing a PXE ROM does is request a configuration through
DHCP, with some additional PXE options set to indicate that it wants
to netboot. It expects a reply that mirrors some of these options, and
DHCP request with additional PXE options set to indicate that it wants
to netboot (on a lower level it is `DHCPDISCOVER` with
[Option 60](https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol#DHCP_client_vendor_identification)).
It expects a reply that mirrors some of these options, and
includes boot instructions in addition to network configuration.

The normal way of providing these options is to edit your DHCP
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