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Topic: STP & EtherChannelSwitch
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3.0 Infrastructure

STP & EtherChannel Practice Questions

RSTP/MSTP port states, BPDU protection, and LACP/PAgP EtherChannel bundling at CCNP depth.

One solved question, so you can see how these are marked

What are the three port states utilized by Rapid Spanning Tree Protocol (RSTP / 802.1w)?

Discarding, Learning, Forwarding

RSTP simplifies 802.1D port states down to three states: Discarding, Learning, and Forwarding.

Every question in the set below is marked like this. The answers stay hidden until you pick one.

All 20 STP & EtherChannel questions in this set

Answers and explanations appear when you work through the set above.

  1. Which configuration makes an access interface forward immediately at link up and err-disables the port if a BPDU is received?

    • BPDU Guard with PortFast enabled
    • BPDU Filter with PortFast enabled
    • Root Guard on a designated port
    • Loop Guard on an alternate port

  2. You are configuring LACP between two Cisco Catalyst switches. Which combination of interface modes will successfully negotiate an EtherChannel bundle?

    • On / Active
    • Auto / Desirable
    • Active / Passive
    • Passive / Passive

  3. What standard defines Multiple Spanning Tree Protocol (MSTP), allowing multiple VLANs to be mapped to a single spanning-tree instance?

    • IEEE 802.1D
    • IEEE 802.1w
    • IEEE 802.1s
    • IEEE 802.3ad

  4. Which Spanning Tree feature prevents non-designated ports from unexpectedly transitioning to a forwarding state if unidirectional links cause BPDU loss?

    • BPDU Filter
    • Root Guard
    • Loop Guard
    • UplinkFast

  5. What PAgP mode combination will successfully form an EtherChannel bundle between two Cisco switch ports?

    • Auto / Auto
    • Auto / Desirable
    • On / Desirable
    • Passive / Desirable

  6. What action does Spanning Tree Root Guard take if a superior BPDU is received on an interface where Root Guard is enabled?

    • It is placed in the err-disabled state and stays down until shut/no shut is entered.
    • It is placed in root-inconsistent state and blocks until superior BPDUs stop.
    • It drops the superior BPDU but keeps forwarding frames as a designated port.
    • It moves to the learning state for 30 seconds before becoming the new root port.

  7. How does an interface behave if BPDU Filtering is enabled globally versus enabled per-interface?

    • Global filtering silently drops every BPDU on all ports, while interface filtering only generates a syslog alert for each BPDU.
    • Global applies to PortFast ports, sends BPDUs at link up, and reverts if one arrives; per-port neither sends nor processes BPDUs.
    • Global filtering applies only to trunk ports, while interface filtering applies only to access ports with no PortFast configured.
    • There is no functional difference; the global command simply applies the interface command to every port on the switch.

  8. When configuring load distribution across physical links in a Cisco EtherChannel bundle, which source/destination hashing algorithm parameters can be selected?

    • MAC addresses, IP addresses, or TCP/UDP port numbers
    • BGP AS-path lengths and OSPF interface costs
    • VLAN IDs and CoS values carried in the 802.1Q tag
    • Interface speed, duplex setting, and current utilization

  9. In Rapid Spanning Tree Protocol (IEEE 802.1w), which port role offers an alternate redundant path to the Root Switch if the local Root Port fails?

    • Backup Port
    • Alternate Port
    • Designated Port
    • Disabled Port

  10. On an 802.1Q trunk, what destination MAC address do Cisco PVST+ per-VLAN BPDUs use for VLANs other than VLAN 1?

    • 01:80:C2:00:00:00
    • 01:00:0C:CC:CC:CD
    • 01:00:5E:00:00:01
    • FF:FF:FF:FF:FF:FF

  11. Which combination of LACP negotiation modes will fail to form an operational EtherChannel between two switches?

    • Active (fast rate) to Active
    • Active to Passive
    • Passive to Passive
    • Desirable to Auto

  12. Which three configuration parameters must match identically on two switches for them to belong to the same MSTP region?

    • Bridge priority, hello time, and forward delay timers
    • Region name, revision number, and VLAN-to-instance mapping
    • VTP domain name, native VLAN ID, and trunk status
    • Spanning-tree mode, root guard status, and PortFast setting

  13. What Spanning Tree feature automatically disables a switch interface configured with PortFast if an incoming BPDU packet is received on that port?

    • BPDU Guard
    • BPDU Filter
    • Root Guard
    • Loop Guard

  14. After an 802.1D topology change, the root bridge sends configuration BPDUs with the Topology Change (TC) flag set. What do switches do when they receive them?

    • They reload every switch interface so the new topology is learned from scratch.
    • They shorten MAC table aging from 300 seconds to the forward delay (15 seconds).
    • They erase the running configuration and fall back to the saved startup config.
    • They put every designated port into the blocking state for 45 seconds.

  15. Which three port states are recognized in Rapid Spanning Tree Protocol (802.1w), replacing the five traditional 802.1D STP states?

    • Blocking, Listening, Forwarding
    • Discarding, Learning, Forwarding
    • Discarding, Listening, Forwarding
    • Listening, Learning, Forwarding

  16. In Rapid Spanning Tree Protocol (802.1w), what differentiates an Alternate Port from a Backup Port?

    • Alternate ports back up the designated port on a shared hub segment; backup ports provide a second path to the root bridge.
    • Alternate ports offer another path to the root bridge; backup ports back up a designated port on a shared segment.
    • Alternate ports are in the forwarding state, while backup ports stay in the discarding state until a failure occurs.
    • Backup ports take part in loop prevention, while alternate ports are disabled entirely and never receive BPDUs at all.

  17. Which three configuration parameters must match identically across switches to form a single MST Region in Multiple Spanning Tree Protocol (802.1s)?

    • Root bridge priority, system ID extension, and forward delay
    • Switch hostname, VTP domain name, and trunk encapsulation (802.1Q)
    • MST region name, revision number, and VLAN-to-instance mapping
    • Spanning-tree mode, hello timer, and max age value

  18. What immediate state transition occurs when an interface configured with spanning-tree portfast and spanning-tree bpduguard enable receives a BPDU packet?

    • It moves to the learning state for 15 seconds, then forwards.
    • It is shut down and placed in the err-disabled state.
    • It drops the BPDU and keeps forwarding user traffic normally.
    • It converts itself into an 802.1Q trunk port toward the sender.

  19. In Multiple Spanning Tree Protocol (MSTP), what is the function of Instance 0 (IST / CIST)?

    • It carries CDP frames across the untagged access ports between MST regions and legacy switches.
    • It calculates a separate topology reserved only for VLAN 1 inside each region.
    • It ties all MST regions and legacy 802.1D/802.1w bridges into one spanning tree.
    • It assigns virtual IP addresses to the default gateways in each MST region.

  20. In OSPF Graceful Restart (RFC 3623), what role is played by a router operating in Helper Mode?

    • It resets the adjacency and resends full Database Description packets so the restarting router can resync.
    • It keeps the adjacency and forwards via the restarting router during the grace period, if the topology stays stable.
    • It takes over the active supervisor role for the restarting switch until that switch finishes reloading.
    • It raises its interface costs to the maximum (65535) so traffic avoids the restarting router during the grace period.