NSX-T Global Tunnel Endpoint MTU automatically changes to default value of 1700 after upgrade to 4.1.1

Products

• VMware NSX

Issue/Introduction

• The environment has been upgraded from 3.2.x or 4.0.x to 4.1.1
• A custom MTU value was set previously. This value has reverted to the default MTU value of 1700
• NSX-T Manager UI shows this under System > Fabric > Settings > Global Fabric Settings > Tunnel Endpoint
• The MTU value is not set in the Edge Uplink Profile
• The Edge fp-ethX interfaces now show the default MTU value

edge> get interface fp-eth0
<date> UTC <time>
Interface: fp-eth0
  ID: 0
  Link status: up
  MAC address: <mac>
  MTU: 1700  

Environment

VMware NSX-T Data Center

VMware NSX

Resolution

This issue is resolved in VMware NSX 4.1.2

Workaround for version prior to 4.1.2:

After the Upgrade, go to System > Fabric > Settings > Global Fabric Settings > Tunnel Endpoint and change to the preferred MTU.

Note: In the fixed version and later, the Global Tunnel Endpoint MTU is changed to 1700 after the upgrade only if the MTU was 1600 before the upgrade.

Additional Information

Impact/Risks:
Traffic that passes through the Edge may be affected if the MTU is set greater than 1700 before the upgrade. For example, if MTU is 9000, the Global “Tunnel Endpoint” MTU value will be changed to 1700 post upgrade. This change will only be pushed if the MTU value isn't set in the Uplink Profile used by the Edge. 

Note: The Uplink Profile MTU setting takes precedence over the Global Fabric Settings.