Which feature allows SAN switches to accept multiple WWPN registrations on a single port?

DCB (Data Center Bridging) is an IEEE 802.1 Ethernet enhancement providing lossless transport for FCoE traffic and does not control WWPN registration on Fibre Channel switch ports.

ISL Tracking monitors the state of inter-switch links and propagates link failures to connected edge ports to trigger failover, which is unrelated to accepting multiple WWPN registrations on a single port.

SCM (Storage Configuration Manager) is a storage provisioning and management utility and does not provide port-level WWPN multiplexing capability on SAN switches.

NPM (N_Port Multiplexing) is the switch-side feature that enables a single physical Fibre Channel port to accept and register multiple World Wide Port Names simultaneously, which is required when hosts use N_Port ID Virtualization (NPIV) to present multiple virtual HBAs. This allows virtualized servers running multiple VMs to each have a distinct WWPN identity on the SAN fabric through a single physical connection. Without NPM enabled on the switch port, the fabric would reject additional WWPN login requests from the same physical port.