Spanning Tree Edge Ports; Spanning Tree Network Ports; Spanning Tree Normal Ports; Understanding Bridge Assurance - Cisco Nexus 3000 Series Configuration Manual

Understanding Bridge Assurance

Spanning Tree Edge Ports

Edge ports, which are connected to hosts, can be either an access port or a trunk port. The edge port interface
immediately transitions to the forwarding state, without moving through the blocking or learning states. (This
immediate transition was previously configured as the Cisco-proprietary feature PortFast.)
Interfaces that are connected to hosts should not receive STP bridge protocol data units (BPDUs).
If you configure a port connected to another switch as an edge port, you might create a bridging loop.
Note

Spanning Tree Network Ports

Network ports are connected only to switches or bridges. Configuring a port as a network port while Bridge
Assurance is enabled globally, enables Bridge Assurance on that port.
Note If you mistakenly configure ports that are connected to hosts or other edge devices as spanning tree network
ports, those ports automatically move into the blocking state.

Spanning Tree Normal Ports

Normal ports can be connected to either hosts, switches, or bridges. These ports function as normal spanning
tree ports.
The default spanning tree interface is a normal port.
Understanding Bridge Assurance
You can use Bridge Assurance to protect against certain problems that can cause bridging loops in the network.
Specifically, you use Bridge Assurance to protect against a unidirectional link failure and a device that continues
to forward data traffic when it is no longer running the spanning tree algorithm.
Note Bridge Assurance is supported only by Rapid PVST+ and MST. Legacy 802.1D spanning tree does not
support Bridge Assurance.
Bridge Assurance is enabled by default and can only be disabled globally. Also, Bridge Assurance can be
enabled only on spanning tree network ports that are point-to-point links. Finally, both ends of the link must
have Bridge Assurance enabled.
With Bridge Assurance enabled, BPDUs are sent out on all operational network ports, including alternate and
backup ports, for each hello time period. If the port does not receive a BPDU for a specified period, the port
moves into the blocking state and is not used in the root port calculation. Once that port receives a BPDU, it
resumes the normal spanning tree transitions.
Cisco Nexus 3000 Series NX-OS Layer 2 Switching Configuration Guide, Release 6.x
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Configuring STP Extensions
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