Understanding Root Guard; Configuring Stp Extensions; Stp Extensions Configuration Guidelines - Cisco Nexus 3000 Series Configuration Manual

Configuring STP Extensions

Loop Guard can be enabled only on network and normal spanning tree port types.
Note
You can use Loop Guard to determine if a root port or an alternate/backup root port receives BPDUs. If the
port does not receive BPDUs, Loop Guard puts the port into an inconsistent state (blocking) until the port
starts to receive BPDUs again. A port in the inconsistent state does not transmit BPDUs. If the port receives
BPDUs again, the protocol removes its loop-inconsistent condition, and the STP determines the port state
because such recovery is automatic.
Loop Guard isolates the failure and allows STP to converge to a stable topology without the failed link or
bridge. Disabling Loop Guard moves all loop-inconsistent ports to the listening state.
You can enable Loop Guard on a per-port basis. When you enable Loop Guard on a port, it is automatically
applied to all of the active instances or VLANs to which that port belongs. When you disable Loop Guard, it
is disabled for the specified ports.

Understanding Root Guard

When you enable Root Guard on a port, Root Guard does not allow that port to become a root port. If a
received BPDU triggers an STP convergence that makes that designated port become a root port, that port is
put into a root-inconsistent (blocked) state. After the port stops sending superior BPDUs, the port is unblocked
again. Through STP, the port moves to the forwarding state. Recovery is automatic.
Root Guard enabled on an interface applies this functionality to all VLANs to which that interface belongs.
You can use Root Guard to enforce the root bridge placement in the network. Root Guard ensures that the
port on which Root Guard is enabled is the designated port. Normally, root bridge ports are all designated
ports, unless two or more of the ports of the root bridge are connected. If the bridge receives superior BPDUs
on a Root Guard-enabled port, the bridge moves this port to a root-inconsistent STP state. In this way, Root
Guard enforces the position of the root bridge.
You cannot configure Root Guard globally.
You can enable Root Guard on all spanning tree port types: normal, edge, and network ports.
Note
Configuring STP Extensions

STP Extensions Configuration Guidelines

When configuring STP extensions, follow these guidelines:
• Configure all access and trunk ports connected to hosts as edge ports.
• Bridge Assurance runs only on point-to-point spanning tree network ports. You must configure each
• Loop Guard does not run on spanning tree edge ports.
• Enabling Loop Guard on ports that are not connected to a point-to-point link will not work.
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side of the link for this feature.
Cisco Nexus 3000 Series NX-OS Layer 2 Switching Configuration Guide, Release 6.x
Understanding Root Guard
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