Zyxel XGS1935-52 – 10Gb LACP ports stuck in blocking state with two Internet links

giannidimanno · January 23

Hi everyone,
I’m experiencing an issue with an LACP configuration on a Zyxel XGS1935-52 and I’d like to compare notes with anyone who has experience with this model.

In my datacenter I have two incoming 10 Gbit/s SFP+ links, representing:

one primary Internet connection
one backup Internet connection

Both links terminate on the same switch and are connected to ports 49 and 50 (SFP+).

The goal is to aggregate them into a single LACP port-channel configured as follows:

LACP mode: active
LACP rate: fast

The configuration appears to be applied correctly:

physical links are up
SFP+ modules are properly detected
LACP is enabled on both interfaces

However, after applying the configuration, both interfaces remain in a blocking state and the port-channel never transitions to forwarding.

What’s interesting is that when using a device from another vendor, with the same configuration on the remote side, the LACP bundle comes up correctly and works without any issues. This leads me to believe there may be a specific limitation or configuration requirement on the Zyxel XGS1935-52.

Has anyone encountered a similar issue or knows how to resolve this?

Zyxel_Barry · January 23

Hi @giannidimanno,

I understand you're experiencing an issue with your LACP configuration on the Zyxel XGS1935-52, where the 10Gb SFP+ ports remain in a blocking state.

Here's some guidance to help troubleshoot this issue:

Verify LACP Configuration on Both Ends: Ensure that both the Zyxel XGS1935-52 and the remote device have LACP configured identically for the aggregated links. This includes setting the LACP mode to "active" and the LACP rate to "fast" on both devices. Mismatched LACP configurations can prevent the link aggregation from forming correctly.
Check Media Type for SFP+ Ports: For SFP+ connections using DAC (Direct Attach Copper) cables, explicitly set the Media Type to "DAC 10G" for the SFP+ ports on your Zyxel switch. This can be found under Basic Setting > Port Setup.
Examine STP Status: Spanning Tree Protocol (STP) can cause ports to go into a blocking state if it detects a loop or misconfiguration. Investigate the STP status on the ports involved in the LACP bundle on your Zyxel XGS1935-52. You may need to adjust STP settings or ensure that LACP is properly prioritized to avoid conflicts.
Firmware Version: Ensure your Zyxel XGS1935-52 has the latest firmware installed. Firmware updates often include bug fixes and performance improvements related to LACP and other features.
Port-Channel Status and Statistics: Check the detailed status and statistics of your LACP port-channel on the Zyxel switch. This can provide valuable information about why the ports are blocking.

To assist you further, please provide the following information:

Screenshots of your LACP configuration: This should include the settings for the Link Aggregation Group and the individual member ports on your Zyxel XGS1935-52.
Firmware version: The current firmware running on your Zyxel XGS1935-52.
Network Topology Map: A simple diagram showing how the Zyxel switch is connected to the remote device and the internet links.
Remote Device Configuration: Details of the LACP configuration on the remote device.

Zyxel_Tina · January 23

Hi @giannidimanno,

Welcome to the Zyxel Community!

Regarding the LACP operation, our switch sends LACP packets to negotiate with the peer device. If there's no response from the other end, the port status may change to blocking.

Could you please first check if LACP is enabled on the uplink port of your connected device? Additionally, kindly provide the complete network topology, including the model names of all devices involved.

Zyxel XGS1935-52 – 10Gb LACP ports stuck in blocking state with two Internet links

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