---
title: "W5500 fails auto negotiation with Meraki switch"
url: "https://maker.wiznet.io/forum/15602"
markdown_url: "https://maker.wiznet.io/forum/15602/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "mwizard"
created: "2025-02-22T03:22:49+09:00"
last_activity: "2025-02-22T03:22:49+09:00"
language: "en"
tags: ["W5500"]
views: 3
replies: 1
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W5500 fails auto negotiation with Meraki switch

## Question

Asked by mwizard on 2025-02-22 in Ethernet Chips.

A customer had trouble connecting a W5500 based device with a Cisco Meraki MS125-48LP, whereas it could connect and auto negotiate with a Meraki MX67 Router just fine.

The workaround was to force the MS125 switch into 100 Mbit full duplex.

Some comments from tech support at Meraki:

- The key factor in this issue is the handling of Unidirectional Link Detection (UDLD) frames. On the MX67, the UDLD frames show a Flags value of `1` (Recommended timeout: 0x1, ReSynch: 0x0), whereas on the MS125-48LP, the Flags value is `3` (Recommended timeout: 0x1, ReSynch: 0x1). This difference in UDLD flag settings indicates a variance in link management and synchronization protocols between the two devices.

- Due to architectural differences between the ports of the Cisco Meraki MX67 and the MS125-48LP, the MX67 effectively manages auto-negotiation due to its hardware components and specific handling of UDLD frames with different flag settings. In contrast, the MS125-48LP requires the port to be forced to 100 Megabit full duplex to maintain stable and consistent communication with the W5500 device, eliminating negotiation issues that may arise from the different UDLD flag settings.

  From a networking point of view, this is as deep as it can be analyzed.
  It is very likely that the W5500 device uses UDLD version 1, recommended timeout flag 0x1 and ReSynch flag of 0x0, similar to the MX67.
  In Auto mode, the W5500 device and the MS125-48LP might be unable to agree on compatible link parameters and that's the reason of empty packet captures.

Does the W5500 even support UDLD?

If so, what version?

Is there a list of networking equipment (switches, routers) that are known to be a problem for the W5500?

Does the W5500 comply with IEEE 802.3?

Thanks.

## Replies

### Reply 1 (verified answer) by WIZnet AI assistant (automated answer), 2025-02-22

The W5500 does not support Unidirectional Link Detection (UDLD). The W5500 is designed to support hardwired TCP/IP protocols such as TCP, UDP, ICMP, IPv4, ARP, IGMP, and PPPoE, but UDLD is not among the supported protocols. Regarding compliance, the W5500 does comply with IEEE 802.3 standards, which cover Ethernet networking. This compliance ensures that the W5500 can operate with a wide range of networking equipment that also adheres to these standards. As for a list of networking equipment that may pose compatibility issues with the W5500, there is no official list available. However, issues like the one you described with the Cisco Meraki MS125-48LP can sometimes occur due to differences in how auto-negotiation and other link management protocols are handled by different devices. In such cases, manually configuring the link settings, as you did by forcing the switch to 100 Mbit full duplex, is a common workaround. If you encounter further issues or need more detailed technical support, I recommend reaching out to WIZnet's technical support team or consulting the technical documentation available at [docs.wiznet.io](https://docs.wiznet.io). WIZnet AI Support Team

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Source: https://maker.wiznet.io/forum/15602