---
title: "W5500 driver issues on Raspberry Pi 4"
url: "https://maker.wiznet.io/andrew/projects/w5500-driver-issues-on-raspberry-pi-4/"
markdown_url: "https://maker.wiznet.io/andrew/projects/w5500-driver-issues-on-raspberry-pi-4/md"
type: "UCC: User Created Content"
author: "PedroRGTS"
author_url: "https://forums.raspberrypi.com/viewtopic.php?t=370322https://forums.raspberrypi.com/viewtopic.php?t=370322"
editor: "WIZnet"
editor_url: "https://maker.wiznet.io/"
original_author: "PedroRGTS"
original_url: "https://forums.raspberrypi.com/viewtopic.php?t=370322https://forums.raspberrypi.com/viewtopic.php?t=370322"
published: "2025-11-20"
language: "en"
hardware: ["WIZnet W5500"]
likes: 0
views: 560
comments: 0
source: "WIZnet Makers (https://maker.wiznet.io/)"
---

# W5500 driver issues on Raspberry Pi 4

> W5500 driver issues on Raspberry Pi 4: MAC address changes & ARP confusion explained

Original author: PedroRGTS (source: https://forums.raspberrypi.com/viewtopic.php?t=370322https://forums.raspberrypi.com/viewtopic.php?t=370322)

## Components

- **WIZnet W5500** x 1 ([docs](https://docs.wiznet.io/Product/Chip/Ethernet/W5500))

WIZnet parts: W5500 ([Datasheet](https://docs.wiznet.io/Product/Chip/Ethernet/W5500/datasheet?utm_source=maker&utm_medium=project&utm_campaign=w5500), [product hub](https://maker.wiznet.io/products/w5500/))

## Article

**🔎 Overview**

A Raspberry Pi 4 user integrating a W5500 module noticed two confusing symptoms:

1. **MAC address changed every reboot**

2. **W5500 responded to ARP requests for 0.0.0.0** while waiting for DHCP

These behaviors looked like “bugs,” but the community discussion reveals important networking principles and configuration details that engineers should know when working with hardwired TCP/IP chips like the W5500.

---

**💬 What Happened in the Thread**

A brief curated summary of the most useful points:

- The user enabled W5500 on Raspberry Pi via an overlay and configured the interface with DHCP.

- But since they did **not** set a static MAC, the overlay-generated MAC changed every boot.

- They also noticed that before DHCP assigned an IP, the W5500 was briefly responding to ARP queries for the **0.0.0.0** address.

Community replies explained that:

- Many embedded NIC overlays use a **randomized MAC** if the user doesn’t specify one.

- A device that hasn’t yet received a DHCP lease will often use **0.0.0.0** as “initial IP state.”

- Some TCP/IP stacks reply to ARP for 0.0.0.0 as part of the discovery process or link-probe.

---

**📘 WIZnet Insight**

These findings are consistent with expected W5500 behavior:

**1. MAC address instability**

- W5500 does **not** auto-generate a MAC address.

- If the host platform (like Raspberry Pi dtoverlay) does not set one, you get:
  - **default / random** MAC
  - Or occasionally a fallback MAC if the driver implements one

**Recommendation:**
Always specify a MAC in /etc/network/interfaces or via NetworkManager/udev rule.

---

**2. ARP response at 0.0.0.0**

This can happen when:

- W5500 is initialized but **DHCP has not yet completed**, and

- The driver’s ARP handler is active

- The chip is still holding its default IP of **0.0.0.0**

This ARP behavior is common on many NICs during DHCP and is not harmful.

**Recommendation:**

- Ensure DHCP is configured with retry logic

- Optionally assign a **static IPv4 address** or a “DHCP hint” IP if the network allows

---

**📐 Best Practices for Using W5500 on Linux Hosts**

To avoid these confusions:

1. **Manually assign MAC**
   Example udev rule:

2. ACTION=="add", SUBSYSTEM=="net", ATTR{address}="02:08:dc:11:22:33"

3. **Lock the IP strategy**
  - Either DHCP with static mapping on the router
  - Or static IP config on the Pi

4. **Ensure initialization order**
  - SPI → Reset → MAC → IP setup → Open sockets
  - Avoid starting higher-level services before W5500 is fully configured

---

Source: https://maker.wiznet.io/andrew/projects/w5500-driver-issues-on-raspberry-pi-4/