Troubleshooting SFP Connectivity Issues Between Zyxel XGS1930 and USG Flex 700

Zyxel_Melen · July 19

This FAQ addresses a specific connectivity issue encountered when connecting a Zyxel XGS1930 switch and a Zyxel USG Flex 700 firewall using SFP ports.

Background

SFP (Small Form-factor Pluggable) ports offer high-speed connectivity options for networking devices. While they are generally designed for seamless compatibility, differences in device specifications can sometimes lead to link establishment problems.

Scenario

You are trying to connect a Zyxel XGS1930 switch to a Zyxel USG Flex 700 firewall using SFP modules and fiber cables. While the SFP connection works between two XGS1930 switches, you are unable to establish a link between the XGS1930 and the USG Flex 700. Interestingly, the connection works if you use a media converter between the devices.

Solution

The Zyxel USG Flex 700's SFP ports support a maximum link speed of 1Gbps. The XGS1930 switch, however, may default to negotiating a higher speed. This mismatch in supported speed prevents the link from establishing.

To resolve this issue, follow these steps:

Access the XGS1930 switch's web interface.
Navigate to the SFP port configuration for the port connected to the USG Flex 700.
Locate the "Speed/Duplex" setting.
Change the setting from "auto-nego" to either "auto-1G" or "fix 1G."
Save the configuration changes.

After completing these steps, the link between the XGS1930 and the USG Flex 700 should establish successfully.

What Could Go Wrong

Incorrect Port Configuration: Double-check that you are configuring the correct SFP port on the XGS1930 switch.
Faulty SFP Modules or Cables: While unlikely, it's possible that a faulty SFP module or cable is preventing the connection. Try using different modules and cables to isolate the issue.
Firmware Incompatibility: Ensure both the XGS1930 and USG Flex 700 are running the latest compatible firmware versions. Outdated firmware can sometimes cause unexpected behavior.

Additional Information

Always refer to the official Zyxel product documentation for detailed information about specific models and their capabilities.
When troubleshooting network connectivity, it's helpful to systematically test different components and configurations to pinpoint the source of the issue.