Module 5 - STP Concept with Supplemental

Front

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

Back

alternate, designated, 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.

Front

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

Back

lowest MAC address

Front

What is the outcome of a Layer 2 broadcast storm?

Back

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

Front

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? Options: 4096, 32768, 61440, 65535

Back

61440

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.

Front

What is the function of STP in a scalable network?

Back

It disables redundant paths to eliminate Layer 2 loops.

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.

Front

What is a characteristic of spanning tree?

Back

It is enabled by default on Cisco switches.

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.

Front

Which spanning tree standard supports only one root bridge so that traffic from all VLANs flows over the same path?

Back

802.1D

Answer explanation

MST is the Cisco implementation of MSTP, an IEEE standard protocol that provides up to 16 instances of RSTP. PVST+ provides a separate 802.1D spanning-tree instance for each VLAN that is configured in the network. 802.1D is the original STP standard defined by the IEEE and allows for only one root bridge for all VLANs. 802.1w, or RSTP, provides faster convergence but still uses only one STP instance for all VLANs.

Front

What is the purpose of the Spanning Tree Protocol (STP)?

Back

prevents Layer 2 loops

Answer explanation

The Spanning-Tree Protocol (STP) creates one path through a switch network in order to prevent Layer 2 loops.

Front

Which protocol provides up to 16 instances of RSTP, combines many VLANs with the same physical and logical topology into a common RSTP instance, and provides support for PortFast, BPDU guard, BPDU filter, root guard, and loop guard?

Back

MST

Answer explanation

MST is the Cisco implementation of MSTP, an IEEE standard protocol that provides up to 16 instances of RSTP and combines many VLANs with the same physical and logical topology into a common RSTP instance. Each instance supports PortFast, BPDU guard, BPDU filter, root guard, and loop guard. STP and RSTP assume only one spanning-tree instance for the entire bridged network, regardless of the number of VLANs. PVST+ provides a separate 802.1D spanning-tree instance for each VLAN that is configured in the network.

Front

What is the value used to determine which port on a non-root bridge will become a root port in a STP network?

Back

the path cost

Answer explanation

STP establishes one root port on each non-root bridge. The root port is the lowest-cost path from the non-root bridge to the root bridge, indicating the direction of the best path to the root bridge. This is primarily based on the path cost to the root bridge.