Tier-0 Gateway Down, BGP Down in NSX UI

Products

• VMware NSX

Issue/Introduction

Tier-0 Gateway is showing routing down along with both BGP neighbors being down. 

Environment

NSX 4.x

Cause

BGP Autonomous System Number (ASN) may be incorrect

Logs on NSX edge node will show:

2025/10/16 18:05:22.754275 BGP: %NOTIFICATION: received from neighbor ##.###.###.### 2/2 (OPEN Message Error/Bad Peer AS) 0 bytes

2025/10/16 18:05:35.690396 BGP: %NOTIFICATION: received from neighbor ##.###.###.### 2/2 (OPEN Message Error/Bad Peer AS) 0 bytes

Resolution

Verify the AS number for BGP to match the client it is trying to connect to.