Troubleshooting LLDP Neighbor Discovery on USG FLEX 500H with VLANs

Zyxel_Kevin

Question:
What is the cause of LLDP neighbor information not appearing on USG FLEX 500H devices, and how can it be resolved?

Answer:
The primary reason LLDP neighbor information may not be visible on a USG FLEX 500H, especially when using VLANs, is how the device handles untagged LLDP frames.

• Root Cause: LLDP traffic is typically untagged. If a USG FLEX 500H port is configured with only tagged VLANs and no native (untagged) VLAN interface is present, the firewall will discard the incoming untagged LLDP packets.
• Resolution: To ensure the USG FLEX 500H processes LLDP traffic, you must add a native interface (untagged VLAN) to the relevant port(s) where LLDP-enabled devices are connected.