CNA 251 | Ch. 3, Spanning Tree Protocol (STP)

D. Each switch will analyze the sum of all port costs to reach the root and use the path with the lowest cost.

After the election of the root bridge has been completed, how will switches find the best paths to the root bridge? A. Each switch will analyze the sum of the hops to reach the root and use the path with the fewest hops. B. Each switch will analyze the BID of all neighbors to reach the root and use the path through the lowest BID neighbors. C. Each switch will analyze the port states of all neighbors and use the designated ports to forward traffic to the root. D. Each switch will analyze the sum of all port costs to reach the root and use the path with the lowest cost.

designated

All non-root ports that are still permitted to forward traffic on the network are called ____________ ports.

edge

An RSTP ____ port is a switch port that is never intended to be connected to another switch. It immediately transitions to the forwarding state when enabled.

unknown unicast

An ____________ frame is when the switch does not have the destination MAC address in its MAC address table and must forward the frame out all ports, except the ingress port.

show spanning-tree

An administrator is troubleshooting a switch and wants to verify if it is a root bridge. What command can be used to do this?

spanning-tree portfast

An edge port is configured using the ______________ command.

VLAN 1

Assume until otherwise indicated that all ports on all switches are assigned to ________.

0 65,535 32,768

Bridge priority is a value between _ and ______. The default is _____.

original ingress

Broadcast frames are forwarded out of all switch ports, with the exception of the ______________ port.

PVST+

Cisco switches running IOS 15.0 or later, run _____ by default. This version incorporates many of the specifications of IEEE 802.1D-2004.

10 Gb/s = 2/1 1 Gb/s = 4/1 100 Mb/s = 19/10 10 Mb/s = 100/100

Default port costs are defined by the speed at which the port operates. Match the speed to both its revised IEEE and previous IEEE cost specification. (Some numbers used more than once, some numbers are not used.) 0 1 2 3 4 7 10 19 100 10 GB/s 1 GB/s 100 Mb/s 10 Mb/s

B. All the switches send out BPDUs advertising themselves as the root bridge.

During the implementation of Spanning Tree Protocol, all switches are rebooted by the network administrator. What is the first step of the spanning-tree election process? A. Each switch with a lower root ID than its neighbor will not send BPDUs. B. All the switches send out BPDUs advertising themselves as the root bridge. C. Each switch determines the best path to forward traffic. D. Each switch determines what port to block to prevent a loop from occurring.

bridge ID (BID)

Each BPDU contains a ___ that identifies the switch that sent the BPDU. This contains a priority value, the MAC address of the sending switch, and an optional extended system identification.

spanning-tree vlan 1 priority 24576 end spanning-tree vlan 1 secondary end spanning-tree vlan 1 primary end show spanning-tree

Issue the following commands to configure PVST+. Assume you're on the correct switch. Configure the priority for VLAN 1 on S3 to 24576 and return to privileged EXEC mode. Configure S2 to be the secondary root for VLAN 1 and return to privileged EXEC mode. Configure S1 to be the primary root for VLAN 1 and return to privileged EXEC mode. Display the current spanning tree status on S1. (Or complete activity 3.3.1.2, Slide # 3)

Spanning Tree Protocol (STP)

Layer 3 protocols implement a time to live mechanism, which ends looping traffic. As Layer 2 protocols do not have the ability to implement TTL, ___, a loop-avoidance mechanism, was developed to address this.

MSTP = A protocol that allows multiple VLANs to run in a single spanning-tree instance. Rapid PVST+ = An evolution of STP that provides faster convergence. STP = The legacy standard for STP that runs all VLANs in a single spanning-tree instance.

Match the STP protocol with the correct description. (Not all options are used.) Rapid PVST+ STP MSTP A protocol that allows multiple VLANs to run in a single spanning-tree instance. The legacy standard for STP that runs all VLANs in a single spanning-tree instance. An evolution of STP that provides faster convergence. A Cisco enhancement of RSTP to provide a spanning-tree instance for each VLAN.

three (six seconds)

Protocol information can be immediately aged on a port if Hello packets are not received for ____ consecutive Hello times.

2 0

RSTP uses type _, BPDUs, while the original 802.1D STP uses type _, BPDUs.

Spanning Tree Algorithm (STA)

STP and RSTP use the ___ to determine which switch ports on a network must be put in blocking state to prevent loops from occurring.

bridge priority value

The BID field of a BPDU frame contains three separate fields: The ____________ is a customization value that can used to influence which switch becomes the root bridge.

extended system ID

The BID field of a BPDU frame contains three separate fields: The ______________ value is a decimal value added to the bridge priority value in the BID to identify the priority and VLAN of the BPDU frame.

MAC address

The BID field of a BPDU frame contains three separate fields: When two switches are configured with the same priority and have the same extended system ID, the switch having the _____________ with the lowest value will have the lower BID.

Multiple Spanning Tree (MST)

The Cisco implementation of MSTP, which provides up to 16 instances of RSTP and combines many VLANs with the same physical and logical topology into a common RSTP instance.

root bridge

The STA designates a single switch as the __________ and uses it as the reference point for all path calculations.

two

The default hello timer value for STP BPDU frames is ___ seconds.

internal root path cost

The path information, known as the ________________________, is determined by summing up the individual port costs along the path from the switch to the root bridge.

root port

The switch port with the lowest overall path cost to the root bride is automatically assigned the ________ role, because it is the closest to the root bridge.

Disabled port

This layer 2 port does not participate in spanning tree and does not forward frames.

Blocking port

This port is an alternate port and does not participate in frame forwarding. The port receives BPDU frames to determine the location and root ID of the root bridge switch and which port roles each switch port should assume.

Forwarding port

This port is considered part of the active topology. It sends data frames and sends and receives BPDU frames.

Learning port

This port prepares to participate in frame forwarding and begins to populate the MAC address table.

Listening port

This switch port receives BPDU frames, transmits its own BPDU frames, and informs adjacent switches that the switch is preparing to participate in the active topology.

spanning-tree cost [value] no spanning-tree cost

To configure the port cost of an interface, enter the ________________ command in interface configuration mode. You can restore port cost to the default value with the ________________ command.

show spanning-tree

To verify the port and internal root path cost to the root bridge, enter the _______________ command.

True

True or False? All ports on the root bridge are designated ports.

True

True or False? Instability in the content of the MAC address table results from copies of the same frame being received on different ports of the switch.

False

True or False? It is almost always necessary to configure the point-to-point link-type parameter for Rapid PVST+, because it is common to have a shared link-type.

True

True or False? STP assumes one IEEE 802.1D spanning tree instance for the entire bridged network, regardless of the number of VLANs.

False

True or False? Spanning tree is disabled by default on Cisco switches.

True

True or False? The Cisco RSTP implementation maintains the PortFast keyword, using the spanning-tree portfast command for edge port configuration.

show cdp neighbors

Use network documentation if it exists, or use the ______________ command to discover layer 2 topology.

spanning-tree mode rapid-pvst

What command would you issue to configure Rapid PVST+ spanning-tree mode?

clear spanning-tree detected-protocols

What command would you issue to get rid of all Spanning Tree Protocol configurations?

spanning-tree portfast default spanning-tree portfast bpdguard default

What commands can be used to configure portfast and bpduguard across all interfaces from global configuration?

D. Designing a network to use multiple paths between switches to ensure there is no single point of failure.

What is an accurate description of redundancy? A. Configuring a router with a complete MAC address database to ensure that all frames can be forwarded to the correct destination. B. Configuring a switch with proper security to ensure that all traffic forwarded through an interface is filtered. C. Designing a network to use multiple virtual devices to ensure that all traffic uses the best path through the inter-network. D. Designing a network to use multiple paths between switches to ensure there is no single point of failure.

D. Manually remove redundant links in the switched network.

What is one way to correct a spanning tree failure? A. Replace all instances of STP with RSTP. B. Insert redundant links to replace the failed STP links. C. Replace the cables on failed STP links. D. Manually remove redundant links in the switched network.

IEEE 802.1w

What is the alternate name for RSTP?

PVST+

What is the default STP operation mode on Cisco Catalyst switches?

MAC address

What value determines the root bridge when all switches connected by trunk links have default STP configurations?

Listening

When PVST is running over a switched network, which port state can participate in BPDU frame forwarding based on BPDUs received, but does not forward data frames?

MAC database instability

When a loop occurs, it is possible for the MAC address table on a switch to constantly change with the updates from the broadcast frames, which results in _____________________.

ingress port cost

When a switch receives the BPDU, it adds the _________________ of the segment to determine its internal root path cost.

original 802.1D

When the original spanning tree protocol is the context of a discussion, the phrase _____________ spanning tree is used, to avoid confusion.

Root port

Which STP port role is adopted by a switch port if there is no other port with a lower cost to the root bridge?

A. Discarding E. Learning F. Forwarding

Which three port states are used by Rapid PVST+? (Choose three.) A. Discarding B. Blocking C. Trunking D. Listening E. Learning F. Forwarding

B. Edge port D. PortFast

Which two concepts relate to a switch port that is intended to have only end devices attached and intended never to be used to connect to another switch? (Choose two.) A. Bridge ID B. Edge port C. Extended system ID D. PortFast E. PVST+

64 4 12 48

A BID is made up of __ bits, _ for bridge priority, __ for extended system ID and __ for the MAC address.

Shared

A port operating in half-duplex mode connects a switch to a hub that attaches multiple devices.

Point-to-point

A port-operating in full-duplex mode typically connects a switch to a switch and is a candidate for a rapid transition to a forwarding state.

Rapid Spanning Tree Protocol (RSTP)

According to the latest IEEE documentation on spanning tree, IEEE-802-1D-2004, STP has been superseded by ____.

B. Due to high processing demands during a broadcast storm, communication may fail between end stations in the broadcast domain. D. During a broadcast storm, constant changes to the MAC address table prevent a switch from accurately forwarding frames.

Which two issues are the result of a broadcast storm? (Choose two.) A. During a broadcast storm, a switch will forward excessive Layer 2 broadcast traffic to the router, and the router will then forward these broadcasts to its attached networks. B. Due to high processing demands during a broadcast storm, communication may fail between end stations in the broadcast domain. C. In a network saturated with broadcast traffic, new traffic arriving at the switch will be forwarded into the broadcast domain, which further consumes available bandwidth. D. During a broadcast storm, constant changes to the MAC address table prevent a switch from accurately forwarding frames. E. During a broadcast storm, switches with high speed interfaces will forward traffic in half-duplex mode to conserve available bandwidth.

B. The switch port immediately transitions from blocking to the forwarding state. C. The switch port should never receive BPDUs.

Which two statements describe a switch port that is configured with PortFast? (Choose two.) A. The switch port immediately transitions from the listening to the forwarding state. B. The switch port immediately transitions from blocking to the forwarding state. C. The switch port should never receive BPDUs. D. The switch port immediately processes any BPDUs before transitioning to the forwarding state. E. The switch port sends DHCP requests before transitioning to the forwarding state.

spanning-tree link-type {point-to-point | shared}

With Rapid PVST+ the link type is automatically determined, but it can be overridden with an explicit port configuration using the __________________ command.

broadcast storm

Without some loop-avoidance process, each switch may flood broadcasts endlessly. This situation is commonly called a _________________.

show spanning-tree summary

You can view details about the number of ports in the various STP states by using the ________________ command.

Common Spanning Tree (CST)

___ assumes one spanning tree instance for the entire bridged network, regardless of the number of VLANs.

Bridge protocol data unit (BPDU)

____ frames are used by STP to prevent loops.

Rapid Spanning Tree Protocol (RSTP)

____ is an evolution of STP that provides faster convergence than STP.

PVST+

_____ is a Cisco enhancement of STP that provides a separate 802.1D spanning tree instance for each VLAN configured in the network.

Multiple Spanning Tree Protocol (MSTP)

_____ maps multiple VLANs into the same spanning tree instance. The IEEE 802.1s standard, and was inspired by an earlier Cisco implementation.

Alternate

________ ports are selected only on links where neither end is a root port.

Rapid PVST+

_________ is a Cisco enhancement of RSTP that uses PVST+. It provides a separate instance of 802.1w per VLAN.

Alternate and Backup

__________ and _________ ports are in discarding or blocking state to prevent loops

802.1D-2004

___________ is an updated version of the STP standard, incorporating IEEE 802.1w