# Root Bridge Configuration
* Configure one switch as a root bridge in a determined fashion.
* Configure another switch as a secondary root bridge, in case of primary root bridge failure.
ASw1(config)#spanning-tree extend system-id (Priority + 12 bit VLAN ID)
# Manually setting the bridge priority value
ASw1(config)#spanning-tree vlan 10 priority <0-61440>
*Note: Bridge priority in increments of 4096 (Lower is prefered)
* If STP extended system ID is enabled, the default bridge-priority is 32,768 plus the VLAN number
# Primary and Secondary Configurations
ASw1(config)#spanning-tree vlan 10 root [ primary | secondary ]
#Change an interface's per VLAN spanning tree path cost
ASw1(config-if)#spanning-tree vlan 10 cost <1-200000000>
ASw1(config-if)#spanning-tree cost <1-200000000>
*Note: If the vlan parameter is given, the port cost is modified only for the specified VLAN.
#Displaying STP Port Cost Values
ASw1#show spanning-tree interface fastEthernet 0/7 cost
VLAN0001 19
VLAN0006 19
VLAN0010 19
VLAN0100 19
VLAN0101 19
#Displaying STP Port Cost Values of the VLANs
ASw1#show spanning-tree interface fastEthernet 0/7
Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0001 Root FWD 19 128.8 P2p
VLAN0006 Root FWD 19 128.8 P2p
VLAN0010 Root FWD 19 128.8 P2p
VLAN0100 Root FWD 19 128.8 P2p
VLAN0101 Root FWD 19 128.8 P2p
#Configuring STP Port Priority
ASw1(config-if)#spanning-tree port-priority <0-240> (By Default is 128)
*Note: port priority in increments of 16
Ej:
ASw1(config-if)#spanning-tree vlan 10,101 port-priority 64
#Modifying STP Timers
#Number of seconds between generation of config BPDUs
ASw1(config)#spanning-tree vlan 10 hello-time <1-10>
#Maximum number of seconds the information in a BPDU is valid
ASw1(config)#spanning-tree vlan 10 max-age <6-40>
#Number of seconds for the forward delay timer
ASw1(config)#spanning-tree vlan 10 forward-time <4-30>
#Redundant Link Convergence
* PortFast - Enables fast connectivity to be established on access-layer switch ports to workstations that are booting.
* UplinkFast - Enables fast-uplink failover on an access-layer switch when dual up-links are connected into the distribution layer.
* BackboneFast - Enables fast convergence in the network backbone or core layer switches after a spanning-tree topology change occurs.
#PortFast
*Note:
*Port Fast Shortens the Listening and Learning states
*When a workstation link comes up, the switch imedietly moves the PortFast port into Forwarding state. Spanning-Tree loop detection
is still in operation, however, and the port moves into Blocking state if a loop is ever detected on the port.
* By default PortFast is disabled on all switch ports.
# Configure PortFast By Default
ASw1(config)#spanning-tree portfast default
# configure PortFast on specific switch port
ASw1(config-if)#spanning-tree portfast
*Note: One other benefits of PortFast is that Topology Change Notification (TCN)
#UplinkFast
* If the primary uplink went down, up to 50 seconds could elapse before the redundant uplink could be used.
* With UplinkFast feature, when the primary root port uplink fails, another blocked uplink immediately can be brought up for use.
ASw1(config)#spanning-tree uplinkfast
ASw1(config)#spanning-tree uplinkfast max-update-rate <0-65535>
*Note:
*The command is not allowed on the root bridge Switch
*Range 0 to 65,535 pps (Packets Per Second)
ASw1#show spanning-tree uplinkfast
UplinkFast is enabled
Station update rate set to 150 packets/sec.
UplinkFast statistics
-----------------------
Number of transitions via uplinkFast (all VLANs) : 2
Number of proxy multicast addresses transmitted (all VLANs) : 0
Name Interface List
-------------------- ------------------------------------
VLAN1 Fa1/14(fwd), Fa1/15
#BackboneFast
* BackboneFast is simple to configure and operates by short-circuiting the Max-Age timerwhen needed.
* BackboneFast shortens the time a switch waits to detect a root path failure, ports still must go through full-length
Forward Delay timer intervals during the Listening and Learning states.
ASw1(config)#spanning-tree backbonefast
ASw1#show spanning-tree backbonefast
BackboneFast is enabled
BackboneFast statistics
-----------------------
Number of transition via backboneFast (all VLANs) : 0
Number of inferior BPDUs received (all VLANs) : 0
Number of RLQ request PDUs received (all VLANs) : 0
Number of RLQ response PDUs received (all VLANs) : 0
Number of RLQ request PDUs sent (all VLANs) : 0
Number of RLQ response PDUs sent (all VLANs) : 0
*Note: RLQ (Root Link Query)
ASw1#show spanning-tree brief
VLAN1
Spanning tree enabled protocol ieee
Root ID Priority 32768
Address c200.11dc.0000
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32768
Address c200.11dc.0000
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Designated
Name Port ID Prio Cost Sts Cost Bridge ID Port ID
-------------------- ------- ---- ----- --- ----- -------------------- -------
FastEthernet1/14 128.55 128 19 FWD 0 32768 c200.11dc.0000 128.55
FastEthernet1/15 128.56 128 19 FWD 0 32768 c200.11dc.0000 128.56
#Verify STP
DSw1#show spanning-tree vlan 10
VLAN0010
Spanning tree enabled protocol ieee
Root ID Priority 10
Address 001d.45a8.4080
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 10 (priority 0 sys-id-ext 10)
Address 001d.45a8.4080
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19 128.3 P2p
Fa0/2 Desg FWD 19 128.4 P2p
Fa0/3 Desg FWD 19 128.5 P2p
Fa0/4 Desg FWD 19 128.6 P2p
Fa0/24 Desg FWD 19 128.26 P2p
DSw1#show spanning-tree vlan 102
VLAN0102
Spanning tree enabled protocol ieee
Root ID Priority 102
Address 001d.a209.9980
Cost 19
Port 26 (FastEthernet0/24)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 4198 (priority 4096 sys-id-ext 102)
Address 001d.45a8.4080
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19 128.3 P2p
Fa0/2 Desg FWD 19 128.4 P2p
Fa0/3 Desg FWD 19 128.5 P2p
Fa0/4 Desg FWD 19 128.6 P2p
Fa0/24 Root FWD 19 128.26 P2p
ASw1#show spanning-tree vlan 501
VLAN0501
Spanning tree enabled protocol ieee
Root ID Priority 33269
Address 000c.853e.cf00
Cost 38
Port 8 (FastEthernet0/7)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 33269 (priority 32768 sys-id-ext 501)
Address 001e.4977.3c00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7 Root FWD 19 128.8 P2p
Fa0/8 Altn BLK 19 128.9 P2p
