CCNP Enterprise Certification Study Guide: Implementing and Operating Cisco Enterprise Network Core Technologies. Ben Piper
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it or add a new switch to an existing network. Experimenting is a recipe for disaster!
Understand the differences among PVST+, RPVST+, and MST. PVST+ is the original Cisco implementation of the timer-based 802.1D Spanning Tree specification. RPVST+ doesn't use timers, introduces link types, and has a faster convergence time. (R)PVST+ creates a separate Spanning Tree instance for each VLAN. MST lets you map multiple VLANs to a single MST instance, which is useful if you have a large number of VLANs.
Know how to manipulate active and allowed VLANs on a trunk. By default, all VLANs (1-4094) are allowed on a trunk. In order for a VLAN to be allowed and active on one end of a trunk, the VLAN must exist on the switch and not be shut down. If a VLAN is shut down, it will show as allowed but not active. If a VLAN is pruned or blocked, it will show as neither allowed nor active.
Be able to configure all Spanning Tree modes. Although PVST+ is deprecated, its configuration commands are similar to RPVST+, and you may still encounter PVST+ on older gear. Be able to configure (R)PVST+ and MST to customize the root bridge, root ports, and designated ports.
Understand the interactions between RPVST+ and MST. Although this is something that you're more likely to see on an exam than in real life, practicing running RPVST+ and MST concurrently in your lab will solidify your understanding of both. In particular, understand how MST simulates RPVST+.
Exercises
Exercise 2.1
Configure the full-mesh topology in the following figure. Set up 802.1Q trunks among the switches. Configure VLANs 100 and 200 on each switch. Configure one switch to be the primary root for VLAN 100 and another switch to be the primary root for VLAN 200.
Figure 2.8 Physical topology for Exercise 2.1
Exercise 2.2
Configure the primary root for VLAN 100 to be the secondary root for VLAN 200.
Exercise 2.3
Configure the primary root for VLAN 200 to be the secondary root for VLAN 100.
Exercise 2.4
On the switch that's the root for VLAN 100, prune VLAN 100 from all trunks. What happens?
Exercise 2.5
Locate a blocked port in the VLAN 200 topology. Unblock this port using whatever means you wish. (Hint: Try modifying port priority).
Exercise 2.6
Configure MST on the switches. Place VLANs 100 and 200 in MST1.
Exercise 2.7
Take note of the root bridge for MST1. Pick a different switch and make it the root bridge.
Review Questions
You can find the answers in the appendix.
1 Which of the following can reduce the size of a broadcast domain? (Choose two.)Prune VLANsUse 802.1Q trunksUse routed instead of switched interfacesTag the native VLAN
2 You have three switches connected to VLAN 50. They're all running Spanning Tree and have the following base MAC addresses:SW1 0010.84b0.ee30SW2 007c.5d8a.e100SW3 0084.8ede.fdd0Which of the following will be the root for VLAN 50?SW1SW2SW3None of these
3 You have three switches connected to VLAN 10. They have the following base MAC addresses and are set to the default priority:SW1 0010.84b0.ee30SW2 007c.5d8a.e100SW3 0084.8ede.fdd0You plan to add another switch, SW4, to the topology but don't want it to become root. SW4 has a base MAC address of 000c.0f43.01a3. How can you accomplish this?Set SW4's bridge priority to 0Set SW4's bridge priority to 32768Set SW4's bridge priority to 61440Connect SW4 without making any other changes
4 When you enable Spanning Tree on a switch, what does it advertise as the root bridge?The 0000.0000.0000 addressThe highest root bridge ID it receivesThe first root ID it receivesIts own bridge ID
5 How does a switch calculate the lowest cost to the root bridge?Adding its own bridge priority to the bridge priority it receives in a BPDUAdding its own interface cost to the cost it receives in a BPDUAdding its own port priority to the port priority it receives in a BPDUUsing the path via the bridge with the lowest bridge ID
6 You have a switch running IOS 12.4. Which global configuration command will ensure Rapid Spanning Tree is enabled for VLAN 1?spanning-tree rapid-pvstspanning-tree mode pvstspanning-tree mode rapid-pvstspanning-tree vlan 1 mode rapid-pvst
7 How frequently does a switch running Rapid Spanning Tree send configuration BPDUs?Every 1 secondEvery 2 secondsEvery 5 secondsEvery 15 seconds
8 What's the difference between the transmitting bridge ID and the root bridge ID? (Choose two.)The transmitting bridge ID contains information about the switch that sent the BPDU.The transmitting bridge ID doesn't contain any information about the root.The root bridge ID contains the base MAC address of the root bridge.The root bridge ID contains a MAC address based on one of the root bridge's interfaces.
9 You have three connected switches with the following bridge priorities:SW1: 32788SW2: 32770SW3: 36885There are no other switches in this topology. Which of the following can you conclude from this information? (Choose two.)SW2 is the root for VLAN 20.SW1 is the root for VLAN 20.SW2 is in VLAN 2.SW3 will never be the root.
10 Consider the following two switches: SW1 has a base MAC address of 0000.1234.ABC9 with a bridge priority of 0. SW2 has a base MAC of 0000.1234.ABCA with a priority of 0. If both switches are placed in the same VLAN, which will become the Spanning Tree root?SW1SW2NeitherBoth
11 Switch SW1 is running RPVST+ on VLAN 1 and is the root. It's connected to SW2, which has VLAN 1 mapped to the MST1 instance. You want to add VLAN 2 to both switches and make SW2 the root for VLAN 2 without impacting VLAN 1. How can you accomplish this?Make SW2 the root for MST0Map VLAN 2 to MST1Map VLAN 2 to MST0Make SW1 the root for MST1
12 Which of the following must be the same on all switches in order for them to be in the same MST region? (Choose two.)Trunk encapsulationRegion nameAllowed VLANsVLAN-to-instance mappings
13 Which of the following MST configuration commands will map VLANs 100, 400, and 900 to MST3?instance 100,400,900 vlan 3instance 3 vlan 100,400,900spanning-tree mst 1 vlan 100,400,900vlan 100,400,900 instance 3
14 You attempted to configure MST to map VLAN 2 to MST2. However, running show spanning-tree mst 2 gives the error No mst information available for instance(s) 3. What are two possible explanations?You used the wrong show command. Try show spanning-tree vlan 2 instead.VLAN 2 isn't configured on the switch.You failed to type exit in MST configuration mode to save your changes.You failed to issue a write memory command after making the changes.
15 SW1 is running MST and has VLANs 2 through 10 mapped to MST10. SW1 is connected to SW2, which is running RPVST+. There are no physical loops in the topology. All of SW1's ports are forwarding in all VLANs. Which of the following is true? (Choose two.)SW1 is the root for VLAN 1.SW1 is the root for VLAN 2.SW2 is the root for VLAN 1.SW2 is the root for VLAN 2.
16 You want to ensure that a switch always remains root. Which of the following Spanning Tree extensions should you configure?BPDU GuardBPDU FilterRoot Filter
17 Which of the following Spanning Tree extensions can prevent loops caused by a user plugging a hub into a network jack in their cubicle?Loop GuardBPDU FilterBPDU GuardRoot Guard
18 What command provides the simplest way to enable BPDU Guard on all interfaces that are connected to user workstations?The global configuration command errdisable recovery cause bpduguardThe global configuration command spanning-tree bpduguard enableThe interface command spanning-tree bpduguard enableThe global