- When you enable PortFast on a switch port, the port immediately transitions to which state?
Show (Hide) Explanation/ReferencePortFast causes a switch or trunk port to enter the spanning tree forwarding state immediately, bypassing the listening and learning states.
- A. Blocking
- B. Forwarding*
- C. Learning
- D. Listening
- What can you change to select switch as root bridge?
- A. make lower priority*
- B. make higher priority
- C. make lower path cost
- D. make higher path cost
- Which type of port role does not participate in STP calculation?
- A. Listening
- B. Learning
- C. Forwarding
- D. Discarding*
- Which statement about spanning-tree root-bridge election is true?
Show (Hide) Explanation/ReferenceAnswer A is not correct as we can choose which switch to become root bridge by configuring bridge priority. The switch with lowest bridge priority (value) would become the root bridge.
- A. It is always performed automatically
- B. Each VLAN must have its own root bridge*
- C. Each VLAN must use the same root bridge
- D. Each root bridge must reside on the same root switch
For answer B, this paragraph from Cisco confirms it is the correct answer:
“When you implement a root bridge in a switching network, you usually refer to the root bridge as the root switch. Each VLAN must have its own root bridge because each VLAN is a separate broadcast domain. The roots for the different VLANs can all reside in a single switch or in various switches.”
The meaning of answer C is not clear but maybe it means “every VLAN must use the same root bridge” which is not correct as Sw1 can be the root bridge for VLANs 1, 3, 5 but Sw2 can be the root bridge for VLAN 2, 4, 6…
From the quote above we can say answer D is not correct.
- A question about BPDU. What would a PortFast BPDU guard port do when it is configured on a port? (Choose two)
Show (Hide) Explanation/ReferencePortFast BPDU guard prevents loops by moving a nontrunking port into an errdisable state when a BPDU is received on that port. When you enable BPDU guard on the switch, spanning tree shuts down PortFast-configured interfaces that receive BPDUs instead of putting them into the spanning tree blocking state. In a valid configuration, PortFast-configured interfaces do not receive BPDUs. If a PortFast-configured interface receives a BPDU, an invalid configuration exists. BPDU guard provides a secure response to invalid configurations because the administrator must manually put the interface back in service.
- A. err-disabled when port receives BPDUs*
- B. supported only on nontrunking access ports*
- C. forward when port receives BPDUs
- D. supported on trunk ports
- What is one benefit of PVST+?
- A. PVST+reduces the CPU cycles for all the switches in the network
- B. PVST+automatically selects the root bridge location,to provide optimized bandwidth usage.
- C. PVST+allow the root switch location to be optimized per vlan.*
- D. PVST+supports Layer 3 load balancing without loops.
- For which two protocols can PortFast alleviate potential host startup issues? (Choose two)
- A. DHCP*
- B. DNS*
- C. OSPF
- D. RIP
- E. CDP
- Refer to the exhibit. Which statement is true?
Show (Hide) Explanation/ReferenceOnly non-root bridge can have root port. Fa0/11 is the root port so we can confirm this switch is not the root bridge -> A is not correct.
- A. The Fa0/11 role confirms that SwitchA is the root bridge for VLAN 20.
- B. VLAN 20 is running the Per VLAN Spanning Tree Protocol.
- C. The MAC address of the root bridge is 0017.596d.1580.
- D. SwitchA is not the root bridge, because not all of the interface roles are designated.*
From the output we learn this switch is running Rapid STP, not PVST -> B is not correct.
0017.596d.1580 is the MAC address of this switch, not of the root bridge. The MAC address of the root bridge is 0017.596d.2a00 -> C is not correct.
All of the interface roles of the root bridge are designated. SwitchA has one Root port and 1 Alternative port so it is not the root bridge -> D is correct.
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