Overview
Using Subscriber Redundancy Group (SRG), you can now provide redundancy for the subscriber sessions across multiple BNGs located in multiple geographical locations with L3 connectivity over a shared core network through IP or MPLS routing.
SRG provides flexible redundancy pairing on access-link and performs automatic switchovers during dynamic failures or planned events such as maintenance, upgrades, and transitions.
SRG also termed Geo redundancy is a powerful technology that allows session synchronization between two nodes. An active session on one node is mirrored on a standby node, so that when the active link fails, the standby BNG can take over and continue to forward the subscriber session information without any service interruption to the user.
When the subscriber session is up on cnBNG, the control plane BNG synchronizes the state from the active to the backup User Plane (UP) cnBNG. The sessions are mirrored on the standby UP for redundancy by transferring the relevant session state from active UP to standby UP, which can then help in failover (FO) or planned switchover (SO) of sessions from one UP to another. SRG, which is a set of access-interface (or a single access-interface) is introduced in cnBNG, and all subscribers in an SRG would FO or SO as a group.
For more information about the cnBNG control plane, refer to the Cloud Native BNG Control Plane Configuration Guide.
CPEs are agnostic to redundancy. When you enable SRG, CPE peers with the same MAC address and node ID to fall back when there is a failover.
Control plane cNBNG initiates the SRG switchover to the standby node during:
-
Access link failure
-
Core network link failure
-
RP failures
-
Chassis failure