Asymmetric connection is arranged by using PBR mode on a router or creation of asymmetric route. The outbound traffic is only sent to the platform in this case. This arrangement allows to reduce the traffic to be processed by 10 times in some cases. This allows to simplify requirements to the platform.
The reliable HTTP protocol detection and, therefore, filtering and operation of all services is ensured in asymmetric connection. However, detection of some protocols like torrents is complicated in this case. Policing can be applied to outbound traffic only.
To improve detection quality one must use configuration parameter:
asym_mode=1
Furthermore, changing of the destination of generated DPI packets may be required. Normally, DPI sends generated packets to the same interface from which the respective query was received. However, some routers do not support such mode. One can learn where to send the generated DPI packets in this case:
emit_direction=2
Here:
2 - send packets to out_dev interface
1 - send packets to in_dev interface
0 - send packets to the same interface from which the qury packet was received (by default)