Symmetric load balancing is a mechanism of interchanging the source and destination addresses to ensure that bidirectional traffic specific to a particular source and destination address pair flows out of the same member of a trunk group.

non symetric lb drawing
For many monitoring and security applications, bidirectional conversations flowing through the system must be carried on the same port of a LAG. For network telemetry applications, network traffic is tapped and sent to a Cubro G4 Packetmaster, which can hash selected traffic to the application servers' downstream. Each server analyzes the bidirectional conversations. Therefore, the Packetmaster must enable symmetric load balancing to accomplish bidirectional conversations. In addition, the firewall between the Cubro devices can be configured to allow the bidirectional conversations per link of the LAG. These network telemetry applications also require symmetric load balancing on the LAGs between the Cubro devices.

After enabling symmetric load balancing, Flow X upstream traffic (with SIP as, DIP as, layer 4 source port as 32500, layer 4 destination port as 53) and Flow X downstream traffic (with SIP as, DIP as, layer 4 source port as 53, layer 4 destination port as 32500) will hash to the same member link of the LAG resulting in the bidirectional conversation going to the same DPI pool.

symetric lb drawing

Symmetric load balancing or session aware load balancing is supported on all G4 Packetmasters
(EX32, EX32+, EX484-3, EX48400, EX20400)