Spanning-Tree Configuration
It is crucial to understand the impact of a default switch configuration on STP convergence and what configurations can be applied to adjust the default behavior.
PVST+ and Rapid PVST+ Configuration
Complete Table 2-6 to show the default spanning-tree configuration for a Cisco Catalyst 2960 series switch.
Table 2-6 Default Switch Configuration
Feature |
Default Setting |
Enable state |
Enabled on VLAN 1 |
Spanning-tree mode |
|
Switch priority |
|
Spanning-tree port priority (configurable on a per-interface basis) |
|
Spanning-tree port cost (configurable on a per-interface basis) |
1000 Mbps: 100 Mbps: 10 Mbps: |
Spanning-tree VLAN port priority (configurable on a per-VLAN basis) |
|
Spanning-tree VLAN port cost (configurable on a per-VLAN basis) |
1000 Mbps: 100 Mbps: 10 Mbps: |
Spanning-tree timers |
Hello time: seconds Forward-delay time: seconds Maximum-aging time: seconds Transmit hold count: BPDUs |
Document the two different configuration commands that you can use to configure the bridge priority value so that the switch is root for VLAN 1. Use the value 4096 when necessary:
Record the command to verify that the local switch is now root:
S1# _____________________________
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 24577
Address 000A.0033.3333
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24577 (priority 24576 sys-id-ext 1)
Address 0019.aa9e.b000
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 4 128.1 Shr
Fa0/2 Desg FWD 4 128.2 Shr
Explain the purpose of the BPDU guard feature on Cisco switches.
What command interface configuration command enables BPDU guard?
What global configuration command will configure all nontrunking ports as edge ports?
What global configuration command will configure BPDU guard on all PortFast-enabled ports?
The power of PVST+ is that it can load balance across redundant links. By default, the least-favored redundant link is not used. So, you must manually configure PVST+ to use the link.
Figure 2-5 represents a small section of Figure 2-1, showing only two distribution layer switches and one access layer switch. For this example, we have attached PC2 to S1. PC1 is assigned to VLAN 15, and PC2 is assigned to VLAN 25. D1 should be the primary root for VLAN 1 and VLAN 15 and the secondary root for VLAN 25. D2 should be the primary root for VLAN 25 and the secondary root for VLAN 15.
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Figure 2-5 PVST+ Configuration Topology
Based on these requirements, document the commands to modify the default PVST+ operation on D1 and D2.
D1 commands
D2 commands
Document the commands to configure all nontrunking ports on S1 as edge ports with BPDU guard enabled.
Now, assume that you want to run rapid PVST+ on all three switches. What command is required?
Lab - Configuring Rapid PVST+, PortFast, and BPDU Guard (SN 2.3.2.3/SwN 4.3.2.3)
Packet Tracer - Configuring PVST+ (SN 2.3.1.5/SwN 4.3.1.5)
Packet Tracer - Configuring Rapid PVST+ (SN 2.3.2.2/SwN 4.3.2.2)