1. BCMSN LAB 5
Spanning Tree Protocol
Lab 5: Spanning Tree Protocol
Objective
Observe the default spanning tree, configure the Spanning Tree Protocol, and verify the spanning tree configura-
tion.
Lab Topology
For this lab, your network design will include two pods of devices. You will be responsible for configuring the
devices in both pods. The devices on the left side of the topology are in Pod 1. The devices on the right side of the
topology are in Pod 2. P1PC1 and P2PC2 are PC workstations. P1ASW1 and P2ASW2 are access-layer switches.
P1DSW1 and P2DSW2 are distribution-layer switches. The access and distribution layers are two of the three lay-
ers in the Cisco three-layer hierarchical network model, which also includes the core layer.
The Topology diagram below represents the NetMap in the Simulator. To access each of the devices from within
the Simulator, select the device name from the appropriate menu in the Simulator. For example, to access
P1ASW1, click the eSwitches button and select P1ASW1 from the drop-down menu.
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2. BCMSN LAB 5
Spanning Tree Protocol
Command Summary
Command Description
configures an interface
interface fastethernet slot/port
configures a range of interfaces
interface range fastethernet slot/starting_port
– ending_port
displays statistics for packets and the switching
show interface stats
method used
displays spanning tree for a VLAN
show spanning-tree vlan vlan
displays spanning tree detail
show spanning-tree vlan vlan detail
disables an interface; enables an interface
shutdown; no shutdown
configures spanning tree root bridge
spanning-tree vlan vlan_id {root {primary | sec-
ondary]
displays root bridge per VLAN
show spanning tree root
sets spanning tree priority for use in the bridge ID
spanning-tree vlan vlan_id priority priority
sets root guard
spanning-tree guard root
sets uplinkfast
spanning-tree uplinkfast
verifies uplinkfast configuration
show spanning-tree uplinkfast
displays the switchport configuration
show interfaces interface_id switchport
sends an ICMP echo request
ping ip_address
Lab Tasks
Task 1: View Default Spanning Tree
1. Display the spanning tree for VLAN 1. Use the detail option. Use the output to answer questions about
the spanning tree.
a. Which spanning tree is VLAN 1 executing?
________________________________________________________________
b. What is the bridge ID?
________________________________________________________________
c. Why is there no root port?
________________________________________________________________
d. Why are there no blocked ports for VLAN 1?
________________________________________________________________
e. What is the timer value for sending bridge protocol data units (BPDUs)?
________________________________________________________________
f. What is the maximum age for a BPDU?
________________________________________________________________
g. What is the value of the forward delay timer?
________________________________________________________________
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3. BCMSN LAB 5
Spanning Tree Protocol
2. Here is the output from a non-root switch.
P2ASW2#show spanning-tree vlan 1 detail
VLAN0001 is executing the ieee compatible Spanning Tree protocol
Bridge Identifier has priority 32768, sysid 1, address 000a.f435.1200
Configured hello time 5, max age 40, forward delay 30
Current root has priority 32769, address 000a.41bf.0a40
Root port is 3 (FastEthernet0/3), cost of root path is 38
Topology change flag not set, detected flag not set
Number of topology changes 49 last change occurred 08:43:53 ago
Times: hold 1, topology change 35, notification 2
hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0, aging 300
Port 1 (FastEthernet0/1) of VLAN0001 is blocking
Port path cost 19, Port priority 128, Port Identifier 128.1.
Designated root has priority 32769, address 000a.41bf.0a40
Designated bridge has priority 32769, address 000b.5f23.ed00
Designated port id is 128.15, designated path cost 19
Timers: message age 3, forward delay 0, hold 0
Number of transitions to forwarding state: 1
BPDU: sent 43, received 15759
Port 2 (FastEthernet0/2) of VLAN0001 is blocking
Port path cost 19, Port priority 128, Port Identifier 128.2.
Designated root has priority 32769, address 000a.41bf.0a40
Designated bridge has priority 32769, address 000b.5f23.ed00
Designated port id is 128.16, designated path cost 19
Timers: message age 3, forward delay 0, hold 0
Number of transitions to forwarding state: 1
BPDU: sent 46, received 15743
Port 3 (FastEthernet0/3) of VLAN0001 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.3.
Designated root has priority 32769, address 000a.41bf.0a40
Designated bridge has priority 32769, address 000b.5f23.eb00
Designated port id is 128.15, designated path cost 19
Timers: message age 2, forward delay 0, hold 0
Number of transitions to forwarding state: 1
BPDU: sent 161, received 15706
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Spanning Tree Protocol
Port 4 (FastEthernet0/4) of VLAN0001 is blocking
Port path cost 19, Port priority 128, Port Identifier 128.4.
Designated root has priority 32769, address 000a.41bf.0a40
Designated bridge has priority 32769, address 000b.5f23.eb00
Designated port id is 128.16, designated path cost 19
Timers: message age 2, forward delay 0, hold 0
Number of transitions to forwarding state: 1
BPDU: sent 144, received 15692
Port 5 (FastEthernet0/5) of VLAN0001 is forwarding
Port path cost 100, Port priority 128, Port Identifier 128.5.
Designated root has priority 32769, address 000a.41bf.0a40
Designated bridge has priority 32769, address 000a.f435.1200
Designated port id is 128.5, designated path cost 38
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
BPDU: sent 39928, received 0
Review the output above, and answer the following questions.
a. What is the bridge ID?
________________________________________________________________
b. What is the root bridge ID?
________________________________________________________________
c. What is the root port?
________________________________________________________________
d. What is the cost for using the root port?
________________________________________________________________
e. What is the cost of the root path? Why is this cost different?
_________________________________________________________________
f. What is the configured value for hello time, max age, and forward delay?
________________________________________________________________
g. Are these the timers that are in effect? Why or why not?
_________________________________________________________________
Task 2: Configure the Root Bridge
VLAN Root Bridge Secondary Root Bridge
11 P1DSW1 P2DSW2
12 P2DSW2 P1DSW1
1. Using the table above, assign the proper DSW as the root bridge for your VLAN.
2. Display the Spanning Tree for your VLAN to verify that it is the root.
3. Assign the proper DSW as the secondary root bridge for your VLAN. Display the spanning tree for your
VLAN to verify that it is the secondary root.
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Lab Solutions
Task 1: View Default Spanning Tree
1. P1ASW1#show spanning-tree vlan 1 detail
VLAN0001 is executing the ieee compatible Spanning Tree protocol
Bridge Identifier has priority 32768, sysid 1, address 000a.41bf.0a40
Configured hello time 2, max age 20, forward delay 15
We are the root of the spanning tree
Topology change flag not set, detected flag not set
Number of topology changes 43 last change occurred 01:55:00 ago
Times: hold 1, topology change 35, notification 2
hello 2, max age 20, forward delay 15
Timers: hello 1, topology change 0, notification 0, aging 300
Port 1 (FastEthernet0/1) of VLAN0001 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.1.
Designated root has priority 32769, address 000a.41bf.0a40
Designated bridge has priority 32769, address 000a.41bf.0a40
Designated port id is 128.1, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 2
Link type is point-to-point by default
: sent 42807, received 20345
Port 2 (FastEthernet0/2) of VLAN0001 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.2.
Designated root has priority 32769, address 000a.41bf.0a40
Designated bridge has priority 32769, address 000a.41bf.0a40
Designated port id is 128.2, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 2
Link type is point-to-point by default
BPDU: sent 42454, received 20247
Port 3 (FastEthernet0/3) of VLAN0001 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.3.
Designated root has priority 32769, address 000a.41bf.0a40
Designated bridge has priority 32769, address 000a.41bf.0a40
Designated port id is 128.3, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 3651, received 29
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Spanning Tree Protocol
Port 4 (FastEthernet0/4) of VLAN0001 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.4.
Designated root has priority 32769, address 000a.41bf.0a40
Designated bridge has priority 32769, address 000a.41bf.0a40
Designated port id is 128.4, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 3641, received 6
Port 5 (FastEthernet0/5) of VLAN0001 is forwarding
Port path cost 100, Port priority 128, Port Identifier 128.5.
Designated root has priority 32769, address 000a.41bf.0a40
Designated bridge has priority 32769, address 000a.41bf.0a40
Designated port id is 128.5, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is shared by default
BPDU: sent 3768, received 0
a. VLAN 1 is executing IEEE.
b. The bridge ID has priority 32768, sysid 1, and address 000a.41bf.0a40.
c. There is no root port because this is the root bridge.
d. There are no blocked ports for VLAN 1 because all ports on the root bridge are designated ports.
e. The timer value for sending BPDUs is 2 seconds.
f. The maximum age for a BPDU is 20 seconds.
g. The value of the forward delay timer is 15 seconds.
2. a. The bridge ID has priority 32768, sysid 1, and address 000a.f435.1200.
b. The current root has priority 32769 and address 000a.41bf.0a40.
c. The root port is 3 (FastEthernet0/3).
d. The cost for using the root port is 19.
e. The cost of the root path is 38. This device is not directly connected to the root. Path cost is additive.
f. The configured hello time is 5, the max age is 40, and the forward delay is 30.
g. These timers are not in effect. The timers that are in effect are the timers advertised by the root
bridge.
Task 2: Configure the Root Bridge
1. spanning-tree vlan 11 root primary
2. P1DSW1#show spanning-tree vlan 11
VLAN0011
Spanning tree enabled protocol ieee
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7. BCMSN LAB 5
Spanning Tree Protocol
Root ID Priority 24587
Address 000b.5f23.ed00
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24587 (priority 24576 sys-id-ext 11)
Address 000b.5f23.ed00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Port ID Designated Port ID
Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr
---------------- -------- --------- --- --------- -------------------- --------
Fa0/1 128.11 19 FWD 0 24587 000b.5f23.ed00 128.11
Fa0/2 128.12 19 FWD 0 24587 000b.5f23.ed00 128.12
Fa0/3 128.15 19 FWD 0 24587 000b.5f23.ed00 128.15
Fa0/4 128.16 19 FWD 0 24587 000b.5f23.ed00 128.16
3. spanning-tree vlan 11 root secondary
P2DSW2#show spanning-tree vlan 11
VLAN0011
Spanning tree enabled protocol ieee
Root ID Priority 24587
Address 000b.5f23.ed00
Cost 38
Port 15 (FastEthernet0/15)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 28683 (priority 28672 sys-id-ext 11)
Address 000b.5f23.eb00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Port ID Designated Port ID
Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr
---------------- -------- --------- --- --------- -------------------- --------
Fa0/1 128.11 19 FWD 38 28683 000b.5f23.eb00 128.11
Fa0/2 128.12 19 FWD 38 28683 000b.5f23.eb00 128.12
Fa0/3 128.15 19 FWD 19 32779 000a.f435.1200 128.3
Fa0/4 128.16 19 BLK 19 32779 000a.f435.1200 128.4
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8. BCMSN LAB 5
Spanning Tree Protocol
Sample Configuration Scripts
P1DSW1 P1DSW1 (Continued)
version 12.1 interface FastEthernet0/9
! no ip address
hostname P1DSW1 !
! interface FastEthernet0/10
ip subnet-zero no ip address
no ip domain-lookup !
! interface FastEthernet0/23
! switchport trunk encapsulation dot1q
interface FastEthernet0/1 switchport mode trunk
description P1DSW1 to P1ASW1 no ip address
switchport trunk encapsulation dot1q !
no ip address interface FastEthernet0/24
duplex full switchport trunk encapsulation dot1q
speed 100 switchport mode trunk
! no ip address
interface FastEthernet0/2 !
description P1DSW1 to P1ASW1 interface GigabitEthernet0/1
switchport trunk encapsulation dot1q no ip address
no ip address !
duplex full interface GigabitEthernet0/2
speed 100 no ip address
! !
interface FastEthernet0/3 interface Vlan1
description P1DSW1 to P2ASW2 ip address 172.16.1.100 255.255.0.0
switchport trunk encapsulation dot1q shutdown
no ip address !
duplex full interface Vlan99
speed 100 ip address 172.16.99.100 255.255.0.0
! !
interface FastEthernet0/4 ip classless
description P1DSW1 to P2ASW2 ip http server
switchport trunk encapsulation dot1q !
no ip address line con 0
duplex full password cisco
speed 100 login
! line vty 0 4
! password cisco
interface FastEthernet0/5 login
no ip address line vty 5 15
! login
interface FastEthernet0/6 !
no ip address end
!
interface FastEthernet0/7
no ip address
!
interface FastEthernet0/8
no ip address
!
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