Logical Span Port Mirroring session in NSX Causes Destination VM Unreachable

Products

• VMware NSX

Issue/Introduction

• Issues were encountered when configuring a port mirroring session between two Virtual Machines (VMs) in NSX.
• The port mirroring was set up in NSX Manager using the Logical Span method, with source and destination VMs selected. After configuring the session, the IP address of the destination VM became unreachable.

Example of Port Mirroring session with Logical Span type:

Environment

VMware NSX

Cause

• The source VM's traffic was successfully mirrored to the destination VM. However, the destination VM had only one network adapter, which was also configured with the IP address.
• The single adapter was being used for both regular IP communication and receiving the mirrored traffic on the destination VM. When an adapter is used for port mirroring, it may not function properly for standard IP communication due to the dual workload. 

Resolution

As a work around, it is recommended to add a second network adapter to the destination VM. The first adapter will be used for the management IP address and normal network traffic, and the second adapter will be dedicated to receiving the mirrored traffic from the source VM.

Adding a second network adapter allows the destination VM to receive mirrored traffic on the secondary adapter, while the primary adapter continues to handle the management IP, ensuring there is no disruption to existing network connections. This separation resolves the issue of the single adapter being overloaded with dual functions.

Additional Information

Refer to: Add a Port Mirroring Session in NSX