Network traffic disruption on NSX-T 3.0.x/3.1.0/3.1.1 when using ECMP

Products

• VMware NSX

Issue/Introduction

• North South traffic NAT'd on the T0 gateway is intermittently being dropped
• NSX-T Data Center 3.0.0/3.0.1/3.0.2/3.0.3/3.1.0/3.1.1
• T0 Gateway is configured in Active/Standby mode
• BGP is enabled on the T0 Gateway
• ECMP is enabled
• BFD is enabled on the BGP peers but is not UP e.g.

  edge01(tier0_sr)> get bgp neighbor summary

  BFD States: NC - Not configured, AC - Activating,DC - Disconnected
              AD - Admin down, DW - Down, IN - Init,UP - Up
  BGP summary information for VRF default for address-family: ipv4Unicast
  Router ID: 192.168.10.1  Local AS: 64571
  Neighbor                            AS          State Up/DownTime  BFD InMsgs  OutMsgs InPfx  OutPfx
  192.168.10.9                      60698       Estab 01:32:33     DW  2325    1857    13766  1
  192.168.10.19                     60698       Estab 01:32:33     DW  2320    1857    13766  1

Environment

VMware NSX-T Data Center 3.x
VMware NSX-T Data Center

Cause

Network disruption occurs due to a failure to NAT traffic correctly when a traffic flow is hashed across across multiple uplink paths.
This issue impacts NAT'd traffic in a BGP ECMP configuration where BFD is configured but is not UP.

Resolution

This issue is resolved in VMware NSX 3.1.2 available at Broadcom Downloads.
If you are having difficulty finding and downloading software, please review the Download Broadcom products and software KB.

To workaround this issue

•  Resolve the BFD issue and ensure BFD is UP

or

•  Disable BFD on the T0 BGP peers and reboot the Edges