Rapid Pvst; Mst; Stp Extensions - Cisco nexus 5000 series Configuration Manual

Overview

Rapid PVST+

Rapid PVST+ is the default spanning tree mode for the software and is enabled by default on the default
VLAN and all newly created VLANs.
A single instance, or topology, of RSTP runs on each configured VLAN, and each Rapid PVST+ instance on
a VLAN has a single root device. You can enable and disable STP on a per-VLAN basis when you are running
Rapid PVST+.

MST

The software also supports MST. The multiple independent spanning tree topologies enabled by MST provide
multiple forwarding paths for data traffic, enable load balancing, and reduce the number of STP instances
required to support a large number of VLANs.
MST incorporates RSTP, so it also 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).
Changing the spanning tree mode disrupts the traffic because all spanning tree instances are stopped for
Note
the previous mode and started for the new mode.
You can force specified interfaces to send prestandard, rather than standard, MST messages using the
command-line interface.

STP Extensions

The software supports the following Cisco proprietary features:
• Spanning tree port types—The default spanning tree port type is normal. You can configure interfaces
• Bridge Assurance—Once you configure a port as a network port, Bridge Assurance sends BPDUs on
• BPDU Guard—BPDU Guard shuts down the port if that port receives a BPDU.
• BPDU Filter—BPDU Filter suppresses sending and receiving BPDUs on the port.
• Loop Guard— Loop guard prevents the occurrence of loop bridging because of unidirectional link failure
• Root Guard— Root guard prevents a port from becoming a root port or a blocked port. If you configure
OL-25842-01
connected to Layer 2 hosts as edge ports and interfaces connected to Layer 2 switches or bridges as
network ports.
all ports and moves a port into the blocking state if it no longer receives BPDUs. This enhancement is
available only when you are running Rapid PVST+ or MST.
in a point-to-point link.
a port with root guard then the port receives a superior BPDU and it immediately goes to root-inconsistent
(blocked) state.
Cisco Nexus 5000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.1(3)N1(1)
Rapid PVST+
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