Spanning Tree Protocol (STP)refers to IEEE 802.1w and IEEE 802.1s. If this publication is referring to the IEEE 802.1D STP, 802.1D is stated specifically.
When you create fault-tolerant internetworks, you must have a loop-free path between all nodes in a network. Multiple active paths between end stations cause loops in the network that result in network devices learning end station MAC addresses on multiple Layer 2 LAN ports. This condition can result in a broadcast storm, which creates an unstable network.
STP provides a loop-free network at the Layer 2 level. Layer 2 LAN ports send and receive STP frames, which are called Bridge Protocol Data Units (BPDUs), at regular intervals. Network devices do not forward these frames but use the frames to determine the network topology and to construct a loop-free path within that topology. Using the spanning tree topology, STP forces redundant data paths into a blocked state. If a network segment in the spanning tree fails and a redundant path exists, the STP algorithm recalculates the spanning tree topology and activates the blocked path.
Cisco NX-OS also supports Multiple Spanning Tree Protocol (MSTP.The multiple independent spanning tree topology enabled by MSTP provides multiple forwarding paths for data traffic, enables load balancing, and reduces the number of STP instances required to support a large number of VLANs.
MST incorporates Rapid Spanning Tree Protocol (RSTP), which allows rapid convergence. MST improves the fault tolerance of the network because a failure in one instance (forwarding path) does not affect other instances (forwarding paths).
You can configure spanning tree parameters only on Layer 2 interfaces; a spanning tree configuration is not allowed on a Layer 3 interface. For information on creating Layer 2 interfaces, see the Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide.
For details about STP behavior and configuration, see the Cisco Nexus 7000 Series NX-OS Layer 2 Switching Configuration Guide.