NSB: L2 control protocols

Nonstop bridging (NSB) uses the same infrastructure as graceful Routing Engine switchover (GRES) to preserve interface and kernel information. However, NSB also saves Layer 2 Control Protocol (L2CP) information by running the Layer 2 Control Protocol process (l2cpd) on the backup Routing Engine. To use NSB, you must first enable GRES on your routing (or switching) platform.