DHCP Modes

PxeLab supports 3 DHCP modes, configured via the dhcp field in each subnet's settings (interfaces[].subnets[].dhcp). Different subnets on the same interface can use different modes.

Quick Reference

Mode	Assigns IP	Provides PXE Options	Non-PXE Clients	Use Case
server	✅	✅	✅ Normal assignment	PxeLab as sole DHCP server (default mode)
proxy	❌ yiaddr=0 throughout	✅	❌ Ignored	Overlay onto existing DHCP
off	❌	❌	❌ Ignored	DHCP fully disabled

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Mode Details

server (Full DHCP)

PxeLab acts as the sole DHCP server on the network, responding to all clients regardless of PXE requests. This is the default mode.

Behavior:

• Manages the full DHCP lifecycle: Discover → Offer → Request → Ack
• All clients receive IP addresses
• PXE clients additionally get NBP filename and boot script URL (Option 175.178)
• Non-PXE clients receive standard DHCP responses for normal networking

Use Cases:

• New networks where PxeLab is the only DHCP service
• Lab/test environments without existing DHCP infrastructure
• Isolated networks (no upstream DHCP server)

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proxy (Proxy DHCP)

PxeLab only provides PXE-related options. IP addresses are assigned by the existing DHCP server.

Behavior:

• Legacy BIOS and UEFI both use yiaddr=0.0.0.0
• Does not interfere with existing DHCP server address allocation
• Non-PXE clients are completely unaffected
• Does not consume address pool

Use Cases:

• Networks with existing DHCP servers needing PXE boot overlay
• When you don't want to change existing network infrastructure

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off (Disabled)

PxeLab completely disables DHCP on this interface, not processing any DHCP requests.

Behavior:

• Interface acts as if DHCP doesn't exist
• No DHCP responses sent
• Other services (HTTP/TFTP/DNS) on the same interface are unaffected

Use Cases:

• Interface only serves HTTP/TFTP boot files, DHCP handled by another device
• Temporarily disabling DHCP during conflict troubleshooting
• Management interfaces that don't need to provide DHCP

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Decision Flow

When a DHCP request is received, PxeLab determines the mode as follows:

DHCP Request Received
    │
    ├─ Is it a PXE/iPXE client?
    │   ├─ Yes → Check the subnet's DHCP mode
    │   │       ├─ proxy → Handle as proxy mode
    │   │       ├─ server → Handle as server mode
    │   │       └─ off → Ignore
    │   │
    │   └─ No → Check the subnet's DHCP mode
    │           ├─ server → Handle as server mode (assign IP)
    │           ├─ proxy → Ignore (non-PXE clients ignored in proxy mode)
    │           └─ off → Ignore
    │
    └─ Respond to client

Deployment Examples

Example 1: Existing Company DHCP, Overlay PXE

    Company DHCP        PxeLab
  192.168.1.1      192.168.1.100
       │                 │
       │                 │  subnet dhcp: proxy
       │                 │
       │                 └── PXE clients get boot options
       │
       └── All clients get IPs
           Non-PXE clients unaffected by PxeLab

Example 2: New Network, PxeLab Does Everything (Default)

    PxeLab (192.168.1.100)
       │
       │  subnet dhcp: server (default)
       │
       ├── PXE clients: IP + boot options
       ├── Regular clients: IP + network config
       └── No other DHCP conflicts

Example 3: Dual Interface — Management + Business

interfaces:
  - name: eth0       # Management
    ip: 10.0.0.1
    subnets:
      - cidr: 10.0.0.0/24
        dhcp: server # Management segment DHCP
        pool: 10.0.0.100-10.0.0.200

  - name: eth1       # Business, PXE overlay
    ip: 192.168.1.100
    subnets:
      - cidr: 192.168.1.0/24
        dhcp: proxy  # Don't interfere with company DHCP

Example 4: File Serving Only

interfaces:
  - name: eth0
    ip: 192.168.1.100
    subnets:
      - cidr: 192.168.1.0/24
        dhcp: off     # DHCP handled by other device
    tftp: true        # Only provide TFTP
    http: true        # Only provide HTTP
    bootloader: grub2

Note: tftp/http/bootloader are interface-level settings; dhcp is a subnet-level setting.

Web UI Configuration

In the PxeLab interface, DHCP mode is set per subnet: Basic Config → Service Config → DHCP, edit an interface, and pick the "DHCP Mode" in each subnet row. Different subnets under the same interface can have different modes.