NSX-T Manager alarms indicating Inter-SR BGP session down

Products

• VMware NSX-T Data Center
• VMware NSX
• VMware NSX Networking

Issue/Introduction

Inter Tier-0 SR False BGP Neighbor Down Alarms

False BGP neighbor down alarms have been triggered for Inter Tier-0 SR.

• Deployment Mode: T0 Gateways are deployed in Active-Active mode.
• Routing Configuration: Inter-SR routing is enabled.
• BGP Configuration: Initially disabled, with ‘Inter SR iBGP’ enabled. The routing state remains operational.
• Re-enabling BGP: Upon re-enabling BGP, alarms indicating BGP is down appear in the NSX UI:
  • “In router xxxxxx, BGP neighbor xxxxx (169.x.x.x) is down.”

Environment

VMware NSX-T Data Center

Cause

When the Tier-0 gateway is deployed in Active-Active mode with 'Inter SR iBGP' enabled by default, this issue occurs when BGP configuration is disabled and then re-enabled while 'Inter SR iBGP' remains enabled. 

Resolution

This is a known issue affecting NSX-T Data Center.

Despite the alarms, there is no functional impact as the Inter-SR sessions remain UP and functional. To avoid these alarms in an Active-Active Tier-0 deployment with 'Inter-SR iBGP' enabled under BGP configuration, toggle the 'Inter-SR iBGP' option whenever the BGP configuration is disabled and then re-enabled.

Follow the steps below to resolve the false alarms on the Inter-SR:

1. Disable the Inter-SR iBGP option in the UI or by using the API:

• Navigate to: Networking -> Tier-0 Gateways -> T0 Edit -> BGP
• Disable 'Inter SR iBGP'

2. Enable the Inter-SR iBGP option in the UI or by using the API:

• Navigate to: Networking -> Tier-0 Gateways -> T0 Edit -> BGP
• Enable 'Inter SR iBGP'

Additional Information

Note: This workaround of toggling Inter-SR sessions may disrupt any traffic via Inter-SR.