BGP route learning failure on NSX from upstream

Products

• VMware NSX

Issue/Introduction

- The BGP (in NSX Tier-0 Gateway) was not learning the default route (0.0.0.0/0), which prevented northbound connectivity from NATed workloads

- On the respective Edge: From T0, in BGP when we do: get forwarding --> no default route learned from BGP

- From BGP debug logs on the Edge where this BGP is configured:

BGP:  #.#.#.#  rcvd UPDATE about 0.0.0.0/0 IPv4 unicast -- DENIED due to: as-path contains our own AS

Environment

VMware NSX

Cause

- As this advertised default route 0.0.0.0/0 AS path has the Local AS (######) that is configured in NSX causing this route to not be learned and is DENIED
- This is a configuration issue in the physical environment, where this same Local AS (which is in NSX) is configured within the physical environment

Resolution

There are 2 ways that can be recommended to resolve the issue:

1. Identify the duplicate AS that is configured in the physical environment and change that AS number
or 
2. Change the Local AS number in NSX to be a different one than those used in the physical environment. And then this Local AS should be updated in all the BGP neighbor configuration so that the BGP can come up and the default route being learnt

Additional Information

Related KB: Troubleshooting NSX BGP