Reference Guide

----------------------------------------------------------------------
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 configure 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 configuration overwrites an
existing root guard configuration 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 traffic from flowing through it. For example, when you configure 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 traffic
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 traffic 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 configuration 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
● Modify the hello-time (in seconds) in CONFIGURATION mode (1 to 10, default 2). With large configurations (involving more
number of ports), Dell EMC recommends increasing the hello-time.
spanning-tree vlan vlan-id hello-time seconds
● Modify the max-age (in seconds) in CONFIGURATION mode (6 to 40, default 20).
spanning-tree vlan vlan-id max-age seconds
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Layer 2