Module 5 - STP Concept with Supplemental

Refer to the exhibit. What are the possible port roles for ports A, B, C, and D in this RSTP-enabled network?

• alternate, root, designated, root

• designated, root, alternate, root

• alternate, designated, root, root

• designated, alternate, root, root

Answer explanation

Because S1 is the root bridge, B is a designated port, and C and D root ports. RSTP supports a new port type, alternate port in discarding state, that can be port A in this scenario.

Which three components are combined to form a bridge ID?

• Which three components are combined to form a bridge ID?

• IP address

• extended system ID

• MAC address

• bridge priority

Answer explanation

The three components that are combined to form a bridge ID are bridge priority, extended system ID, and MAC address.

In which two port states does a switch learn MAC addresses and process BPDUs in a PVST network? (Choose two.)

• blocking

• disabled

• forwarding

• learning

• listening

Answer explanation

Switches learn MAC addresses at the learning and forwarding port states. They receive and process BPDUs at the blocking, listening, learning, and forwarding port states.

If no bridge priority is configured in PVST, which criteria is considered when electing the root bridge?

• lowest IP address

• lowest MAC address

• highest IP address

• highest MAC address

Which two network design features require Spanning Tree Protocol (STP) to ensure correct network operation? (Choose two.)

• static default routes

• implementing VLANs to contain broadcasts

• redundant links between Layer 2 switches

• link-state dynamic routing that provides redundant routes

• removing single points of failure with multiple Layer 2 switches

What is the outcome of a Layer 2 broadcast storm?

• Routers will take over the forwarding of frames as switches become congested.

• New traffic is discarded by the switch because it is unable to be processed.

• CSMA/CD will cause each host to continue transmitting frames.

• ARP broadcast requests are returned to the transmitting host.

When the show spanning-tree vlan 33 command is issued on a switch, three ports are shown in the forwarding state. In which two port roles could these interfaces function while in the forwarding state? (Choose two.)

• disabled

• designated

• root

• alternate

• blocked

Answer explanation

The role of each of the three ports will be either designated port or root port. Ports in the disabled state are administratively disabled. Ports in the blocking state are alternate ports.

A set of switches is being connected in a LAN topology. Which STP bridge priority value will make it least likely for the switch to be selected as the root?

• 4096

• 32768

• 61440

• 65535

Answer explanation

The STP bridge priority is a two byte number, but it can only be customized in increments of 4096. The smaller number is preferred, but the largest usable priority value is 61440.

What is the function of STP in a scalable network?

• It decreases the size of the failure domain to contain the impact of failures.

• It protects the edge of the enterprise network from malicious activity.

• It disables redundant paths to eliminate Layer 2 loops.

• It combines multiple switch trunk links to act as one logical link for increased bandwidth.

Answer explanation

STP is an important component in a scalable network because it allows redundant physical connections between Layer 2 devices to be implemented without creating Layer 2 loops. STP prevents Layer 2 loops from forming by disabling interfaces on Layer 2 devices when they would create a loop.

What is a characteristic of spanning tree?

• It is enabled by default on Cisco switches.

• It has a TTL mechanism that works at Layer 2.

• It prevents propagation of Layer 2 broadcast frames.

• It is used to discover information about an adjacent Cisco device.

Answer explanation

Spanning tree does work at Layer 2 on Ethernet-based networks and is enabled by default, but it does not have a TTL mechanism. Spanning tree exists because Layer 2 frames do not have a TTL mechanism. Layer 2 frames are still broadcast when spanning tree is enabled, but the frames can only be transmitted through a single path through the Layer 2 network that was created by spanning tree. Cisco Discovery Protocol (CDP) is used to discover information about an adjacent Cisco device.