Understanding Nonstop Bridging on EX Series Switches
You can configure nonstop bridging (NSB) to provide resilience for Layer 2 protocol sessions on a Juniper Networks EX Series Ethernet Switch or on an EX Series Virtual Chassis with redundant Routing Engines.
NSB operates by synchronizing all protocol information for NSB-supported Layer 2 protocols between the primary and backup Routing Engines. If the switch has a Routing Engine switchover, the NSB-supported Layer 2 protocol sessions remain active because all session information is already synchronized to the backup Routing Engine. Traffic disruption for the NSB-supported Layer 2 protocol is minimal or nonexistent as a result of the switchover. The Routing Engine switchover is transparent to neighbor devices, which do not detect any changes related to the NSB-supported Layer 2 protocol sessions on the switch.
For a list of the EX Series switches and Layer 2 protocols that support NSB, see EX Series Switch Software Features Overview and EX Series Virtual Chassis Software Features Overview.
Nonstop bridging provides a transparent switchover mechanism only for Layer 2 protocol sessions. Nonstop active routing (NSR) provides a similar mechanism for Layer 3 protocol sessions. See Understanding Nonstop Active Routing on EX Series Switches.