Reference Guide

Executing IEEE compatible Spanning Tree Protocol
Root ID Priority 24577, Address 90b1.1cf4.a523
Root Bridge hello time 2, max age 20, forward delay 15
Bridge ID Priority 24577, Address 90b1.1cf4.a523
We are the root of VLAN 1
Configured hello time 2, max age 20, forward delay 15
Interface Designated
Name PortID Prio Cost Sts Cost Bridge ID PortID
----------------------------------------------------------------------
ethernet1/1/5 128.276 128 500 FWD 0 24577 90b1.1cf4.a523 128.276
ethernet1/1/6 128.280 128 500 LRN 0 24577 90b1.1cf4.a523 128.280
Interface
Name Role PortID Prio Cost Sts Cost Link-type Edge
-------------------------------------------------------------
ethernet1/1/5 Desg 128.276 128 500 FWD 0 AUTO No
ethernet1/1/6 Desg 128.280 128 500 LRN 0 AUTO No
Loop guard
This information explains how to congure loop guard on an interface.
• Enable loop guard on a per-port or port-channel interface in INTERFACE mode.
spanning-tree guard {loop | root | none}
– loop — Enables loop guard on an interface.
– root — Enables root on an interface.
– none — Enables the guard mode to none.
• Disable loop guard on a port or port-channel interface in INTERFACE mode.
no spanning-tree guard loop
Port enabled with loop guard conditions
• Loop guard is supported on any STP-enabled port or port-channel interface in RPVST+ mode.
• You cannot enable root guard and loop guard at the same time on an STP port — the loop guard conguration overwrites an existing
root guard conguration and vice versa.
• Enabling BPDU guard and loop guard at the same time on a port results in a port that remains in a Blocking state and prevents trac
from owing through it. For example, when you congure both Portfast BPDU guard and loop guard:
– If a BPDU is received from a remote device, BPDU guard places the port in an Err-Disabled Blocking state and no trac forwards
on the port.
– If no BPDU is received from a remote device which was sending BPDUs, loop guard places the port in a Loop-Inconsistent Blocking
state and no trac forwards on the port.
• When used in a PVST+ network, STP loop guard performs per-port or per port-channel at a VLAN level. If no BPDUs are received on a
port-channel interface, the port or port-channel transitions to a Loop-Inconsistent (Blocking) state only for this VLAN.
Global parameters
All non-root bridges accept the timer values on the root bridge.
Forward-time
Amount of time required for an interface to transition from the Discarding to the Learning state or from the
Learning to the Forwarding state.
Hello-time Time interval within which the bridge sends BPDUs.
Max-age Length of time the bridge maintains conguration information before it refreshes information by recomputing the
RPVST+ topology.
• Modify the forward-time (in seconds) in CONFIGURATION mode (4 to 30, default 15).
spanning-tree vlan vlan-id forward-time seconds
Layer 2
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