A single IP subnet is used for all subscribers terminated within the redundant BNG nodes. The upside of the option A is that it offers aggregated IP addressing in the network core per pair of redundant BNG nodes. The downside is that the subscriber termination point (active BNG for the SRRP group) is hidden from the network core. Because both BNG nodes share the same IP subnet for the subscribers, the natural routing can cause downstream traffic to be sent to the standby BNG which must shunt the traffic to the active BNG. It is likely that half of the traffic is shunted over the redundant-interface with this approach. This scenario is shown in Figure: Shared subscriber IP space.
Figure: Shared subscriber IP space
