option 43 hex calculator - Aaron Graves, PhDude Replica

DHCP Option 43 Hex Calculator

Convert one or more controller IP addresses into DHCP Option 43 hex format. Supports TLV output (sub-option + length + data), raw data hex, and per-IP conversion.

Controller / Server IPv4 addresses

Use commas, spaces, or new lines to separate multiple addresses.

Sub-option code (hex)

Common value is F1 for many wireless deployments.

Output mode

Byte separator

Prefix output with 0x

Result

What DHCP Option 43 Is and Why Hex Matters

DHCP Option 43 is the Vendor Specific Information option. Network teams often use it to tell devices where to find their management controller during boot. Access points, IP phones, and other hardware can request this field and parse vendor-defined sub-options.

Many DHCP servers ask for a hex string instead of plain IP addresses. That is where this calculator helps: it converts normal IPv4 addresses into the exact byte sequence you can paste into your DHCP configuration.

How Option 43 Encoding Works

TLV structure

The most common pattern is a TLV format:

T = Sub-option code (1 byte, often F1)
L = Length (1 byte, decimal byte count converted to hex)
V = Value (the IP bytes, in network order)

Each IPv4 address contributes 4 bytes. Two IPs therefore have a value length of 8 bytes, which is 08 in hex.

Example

If your controller is 192.168.10.5:

IP bytes = C0 A8 0A 05
Length = 04
Sub-option F1 + Length + Value = F1 04 C0 A8 0A 05

How to Use This Option 43 Hex Calculator

Enter one or more IPv4 addresses.
Leave sub-option at F1 unless your vendor documentation says otherwise.
Choose TLV output for most DHCP Option 43 workflows.
Click Calculate and paste the result into your DHCP server policy/scope.

Common Deployment Scenarios

Single controller

Most small environments use one management endpoint. The output will be short and easy to verify manually.

Multiple controllers for redundancy

If you add two or more controller IPs, this calculator concatenates all bytes in order. Keep in mind that order may influence which target is attempted first by some client implementations.

Different DHCP server formats

Some DHCP interfaces want continuous hex, others accept spaced bytes. Use the separator control to match your platform requirements.

Troubleshooting Mistakes Quickly

Invalid IP: each octet must be 0–255 and you must have exactly four octets.
Wrong sub-option: verify with vendor docs; F1 is common but not universal.
Length mismatch: for TLV mode, length must equal total value bytes.
Wrong scope/VLAN: make sure clients are receiving the intended DHCP policy.
Missing Option 60 dependency: some designs match Vendor Class before sending Option 43.

Quick Validation Checklist Before Production

Confirm client VLAN and DHCP helper path.
Validate Option 43 value in packet captures.
Test one pilot device before broad rollout.
Document the final hex string with date and change ticket.

Used carefully, Option 43 is a reliable way to automate discovery and reduce manual provisioning. Save time, avoid typos, and standardize your DHCP configs with repeatable hex output.