SLB Topology Example

When traffic that arrives from the client to the server needs to be distributed to the virtual server (traffic with destination IP address as VIP), ECMP routing occurs. The destination MAC address of each packet is changed to the MAC address of the real server by the switch hardware in wire speed. In return traffic (from the server to the client), DSR is used to directly forward to the client all traffic returning to the clients. No ECMP routing occurs in backward traffic. The real server returns the packet with the source IP address set to the VIP instead of its own IP address, which is made possible by setting the loopback interface (for example, lo0) in each server participating in the LBG. The loopback interface provides address aliasing for the VIP, but will not respond to ARP requests of the VIP. No NAT is involved in either the forward and reverse direction.