Spanning Tree Part 1 (Page 2 of 2) in pdf

PANNING

REE

ART

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PVST+ and RPVST+ Configuration

Bridge ID Format

spanning-tree mode {pvst | rapid-pvst}

Pri

Sys ID Ext

MAC Address

! Bridge priority

spanning-tree vlan 1-4094 priority 32768

Priority

4-bit bridge priority (configurable from 0 to 61440 in

! Timers, in seconds

increments of 4096)

spanning-tree vlan 1-4094 hello-time 2

spanning-tree vlan 1-4094 forward-time 15

System ID Extension

spanning-tree vlan 1-4094 max-age 20

12-bit value taken from VLAN number (IEEE 802.1t)

MAC Address

! PVST+ Enhancements

48-bit unique identifier

spanning-tree backbonefast

spanning-tree uplinkfast

Path Selection

! Interface attributes

1 Bridge with lowest root ID becomes the root

interface FastEthernet0/1

Prefer the neighbor with the lowest cost to root

spanning-tree [vlan 1-4094] port-priority 128

spanning-tree [vlan 1-4094] cost 19

Prefer the neighbor with the lowest bridge ID

! Manual link type specification

Prefer the lowest sender port ID

spanning-tree link-type {point-to-point | shared}

Optional PVST+ Ehancements

! Enables PortFast if running PVST+, or

PortFast

! designates an edge port under RPVST+

spanning-tree portfast

Enables immediate transition into the forwarding state

(designates edge ports under MST)

! Spanning tree protection

UplinkFast

spanning-tree guard {loop | root | none}

Enables switches to maintain backup paths to root

! Per-interface toggling

BackboneFast

spanning-tree bpduguard enable

Enables immediate expiration of the Max Age timer in

spanning-tree bpdufilter enable

the event of an indirect link failure

MST Configuration

Spanning Tree Protection

Root Guard

spanning-tree mode mst

Prevents a port from becoming the root port

BPDU Guard

! MST Configuration

spanning-tree mst configuration

Error-disables a port if a BPDU is received

name MyTree

Loop Guard

revision 1

Prevents a blocked port from transitioning to listening

after the Max Age timer has expired

! Map VLANs to instances

instance 1 vlan 20, 30

BPDU Filter

instance 2 vlan 40, 50

Blocks BPDUs on an interface (disables STP)

! Bridge priority (per instance)

RSTP Link Types

spanning-tree mst 1 priority 32768

Point-to-Point

Connects to exactly one other bridge (full duplex)

! Timers, in seconds

spanning-tree mst hello-time 2

Shared

spanning-tree mst forward-time 15

Potentially connects to multiple bridges (half duplex)

spanning-tree mst max-age 20

Edge

Connects to a single host; designated by PortFast

! Maximum hops for BPDUs

spanning-tree mst max-hops 20

Troubleshooting

! Interface attributes

show spanning-tree [summary | detail | root]

interface FastEthernet0/1

spanning-tree mst 1 port-priority 128

show spanning-tree [interface | vlan]

spanning-tree mst 1 cost 19

show spanning-tree mst […]

by Jeremy Stretch

v3.0

Spanning Tree Part 1 Page 2

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