NSX Overlay Segments Display "0 Free Ports" in vCenter UI

Products

• VMware NSX

Issue/Introduction

• When viewing port usage for an NSX-backed overlay segment in vCenter Server, you may notice the following:
  • A newly created segment displays 0 capacity, 0 used, and 0 free ports.

• • As virtual machines are attached, the port capacity updates to exactly match the number of connected VMs. The segment will continue to show "0 free ports" because the capacity and used metrics are identical.

Environment

VMware NSX

Cause

This is by design. Unlike traditional vSphere Distributed Switch networking which requires pre-allocating a fixed block of ports NSX uses dynamic, elastic port allocation.

Resolution

No action is required. This behavior is a feature, not a defect. It removes the need for administrators to manually monitor or scale port group capacity, as NSX scales port availability automatically and infinitely based on your environment's workload.

Additional Information

NSX manages these as ephemeral port groups, meaning there is no static "ports-per-segment" ceiling. Instead, capacity is bound by:

• MAC Identifiers per Segment (VNI): Maximum of 2,048 MAC addresses per overlay segment. Exceeding this risks network flooding and performance degradation.
• System-Wide Segment Ports: Capped by the NSX Manager size (Medium: 2,500 ports | Large: 25,000 ports).