[VMC on AWS] Bandwidth does not increase even if ECMP for Route Based IPSec VPN is enabled

Products

• VMware Cloud on AWS

Issue/Introduction

This article provides information why ECMP is not working as expected.

Symptoms:
After 1.7 SDDC release, VMware Cloud on AWS supports Equal-Cost Multi-Path routing (ECMP) with route based IPSec VPN.

Now customers can deploy TGW with ECMP and leverage up to 4 Route Based IPSec VPN tunnels doing ECMP for increased bandwidth.

However the load is not balanced as expected and increased bandwidth is not achieved in some cases.

Cause

In current release (1.8 SDDC release), the load-balancing algorithm is taking as input only IP source and destination (2-tuple). Adding more ECMP VPN tunnels does not linearly scale the bandwidth achieved.

Resolution

This behavior is by design.

Workaround:
To increase bandwidth, do not using same source/destination IP for each session.