how to check whether the backend server in a loadbalancer has bypassed the loadbalancer in a DSR mode while replying to client?

Question

I couldn't find much information on how to verify if DSR mode in a loadbalancer works or not. Is there a way to find whether the loadbalancer is bypassed during a reply from the backend server to the client in case of a Direct Server Return node ?

Answer 1

When using Direct Server Return, the Backend Server will be configured with an additional (loopback)Interface matching the Virtual IP used on the Load Balancer. This allows it reply from the same IP address that the request was sent to. So by design from the client perspective it will look the same.

Best way imo to verify would be to trace the traffic (TCP Dump) and check MAC address (is it from the Real Server or the Load Balancer) Otherwise maybe the load balancer metrics can verify.