DHCP Configuration

PXE booting leverages DHCP (Dynamic Host Configuration Protocol) on a network to enable computers to perform a network boot. When a client PXE boots, it sends a DHCP broadcast to the network. This broadcast is a request for IP address configuration information but also uniquely indicates that the client is PXE-capable and is seeking to boot from the network.

If the local subnet does not contain a PXE server which can respond to the broadcast, the client needs additional information to direct its request to the PXE server.

This can be done in two ways:

DHCP Scope Options

This option requires modifications to the configuration of your DHCP scopes.

Using IP Helpers

This option requires modifications to networking hardware to route specific traffic to the PXE server.

DHCP Scope Options vs IP Helpers?

Reasons to use DHCP scope options to control network boot:

1. Smaller footprint to deploy

2. Maybe no need to talk to the network team

Reasons not to use DHCP scope options to control the network boot:

1. No ability to use DHCP to set the right boot loader

2. DHCP changes can be hard to tweak and test depending on vendor of DHCP

3. Difficult to directly control which machines receive PXE boot offers.

4. More administration needed to allow different boot options to different clients

5. No need to talk to the DHCP team.

When using DHCP options there is no way for the iPXE NBP to automatically detect the options values from the 2PXE server. Instead the URL for the client to contact is configured through DHCP option 175.

NOTE: DHCP Scope Option 175 contains the 2PXE URL and must be in lower case and end with a trailing backslash: https://<serverFQDN>:<port>/