Network performance issues when using IP forwarding in Linux

Products

• VMware vSphere ESXi

Issue/Introduction

You have a linux VM setup with IP forwarding. It has one network interface (for eg ens192) using the vmxnet3 driver, and it has two IP address in different subnets. The rouitng table contains a route for each of the two subnets.

It doesn't forward packets between the subnets as expected. 

Environment

VMware ESXi

Cause

This is expected behaviour of Linux machines with IP forwarding enabled.

Resolution

The two IP addresses must be assigned to two different interfaces. Once this is done, the VM will forward traffic between two interfaces correctly.