← Cloudflare Wan / cloudflare-wan / configuration / appliance / network-options / dhcp
DHCP server options
When the Cloudflare One Appliance is configured as the DHCP server for a LAN, you can attach custom DHCP options to the leases it issues. This is commonly used for:
- Network boot of workstations or kiosks with PXE, PXELINUX, or iPXE (options 43, 60, 66, 67, 175, 209, and 210).
- VoIP phone provisioning (option 66 — TFTP server).
- Vendor-specific client configuration (option 43 with vendor sub-options).
DHCP options can only be configured when the appliance is acting as the DHCP server. They have no effect when the appliance is in DHCP relay mode.
DHCP options are configured via the API and Terraform.
Option format
Each option is defined by three fields:
| Field | Description | Example |
|---|---|---|
option_number |
The DHCP option code (1–254). | 67 |
type |
The value encoding: text, integer, hex, ip. |
text |
value |
The option value, encoded per type. |
boot/x64/pxelinux.0 |
Value type encoding
| Type | Format | Example value |
|---|---|---|
ip |
A dotted-quad IPv4 address. | 10.20.30.40 |
integer |
A decimal integer. | 0 |
text |
A UTF-8 string. | boot/x64/pxelinux.0 |
hex |
A colon-separated sequence of bytes, used for sub-options. | 01:04:aa:bb:cc |
Common network boot options
The most frequently used network boot options are:
| Option | Type | Purpose |
|---|---|---|
| 43 | hex |
Vendor-specific information. The vendor defines the sub-option layout. |
| 60 | text |
Vendor class identifier, typically PXEClient. |
| 66 | text |
TFTP server name. |
| 67 | text |
Boot file name, for example ipxe.pxe or undionly.kpxe. iPXE also accepts a URI, such as an HTTP URL for an iPXE script. |
| 175 | hex |
Client-specific encapsulated options used by Etherboot and iPXE. IANA lists this option as tentatively assigned and does not define its payload. |
| 209 | text |
PXELINUX configuration filename or path, loaded through TFTP. |
| 210 | text |
PXELINUX TFTP path prefix, prepended to option 209. |
For a complete list of standard DHCP option codes, refer to the IANA BOOTP/DHCP parameters registry ↗.
Validation and apply behavior
Before applying a new DHCP options configuration, the appliance:
- Stages the change to a temporary configuration file.
- Validates the syntax with the underlying DHCP server.
- On success, atomically swaps the staged configuration into place and reloads the DHCP server with no service interruption.
- On failure, discards the change and returns the underlying validation error to the API caller. The live DHCP service is never restarted with an unverified configuration.
This means a malformed option will be rejected at apply-time rather than disrupting DHCP service for clients on the LAN.