CCNA Lan Chapter #5
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Which two statements are true about the default operation of STP in a Layer 2 switched environment that has redundant connections between switches? (Choose two.)
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The root switch is the switch with the highest speed ports.
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Decisions on which port to block when two ports have equal cost depend on the port priority and identity.
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All trunking ports are designated and not blocked.
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Root switches have all ports set as root ports.
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Non-root switches each have only one root port.
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Welcome to the fifth chapter of our studies on the Cisco Certified Network Associate’s curriculum on the topic of local area networks, where today we’ll be taking an even further look at these computer networks which are used to connect devices within a relatively short range. What can you tell us?
Quiz Preview
- 2.
Which two statements describe the BIDs used in a spanning tree topology? (Choose two.)
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They are sent out by the root bridge only after the inferior BPDUs are sent.
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They consist of a bridge priority and MAC address.
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Only the root bridge will send out a BID.
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They are used by the switches in a spanning tree topology to elect the root bridge.
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The switch with the fastest processor will have the lowest BID.
Correct Answer(s)
A. They consist of a bridge priority and MAC address.
A. They are used by the switches in a spanning tree topology to elect the root bridge.Explanation
The BIDs (Bridge IDs) used in a spanning tree topology consist of a bridge priority and MAC address. They are used by the switches in a spanning tree topology to elect the root bridge. The bridge priority determines which switch becomes the root bridge, with the lowest priority being preferred. The MAC address is used as a tiebreaker if multiple switches have the same priority. Therefore, the BIDs play a crucial role in determining the root bridge and the overall topology of the spanning tree network.Rate this question:
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- 3.
In which two ways is the information that is contained in BPDUs used by switches? (Choose two.)
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To negotiate a trunk between switches
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To set the duplex mode of a redundant link
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to identify the shortest path to the root bridge
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To prevent loops by sharing bridging tables between connected switches
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To determine which ports will forward frames as part of the spanning tree
Correct Answer(s)
A. to identify the shortest path to the root bridge
A. To determine which ports will forward frames as part of the spanning treeExplanation
BPDUs (Bridge Protocol Data Units) are used by switches in two ways. First, they are used to identify the shortest path to the root bridge. By exchanging BPDUs, switches can determine the path with the lowest cost to reach the root bridge, which helps in building the spanning tree topology. Second, BPDUs are used to determine which ports will forward frames as part of the spanning tree. By analyzing the BPDUs received from neighboring switches, a switch can determine the designated and non-designated ports, and only forward frames through the designated ports to prevent loops in the network.Rate this question:
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- 4.
Which two actions does an RSTP edge port take if it receives a BPDU? (Choose two.)
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immediately loses its edge status
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Inhibits the generation of a TCN
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Goes immediately to a learning state
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Disables itself
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Becomes a normal spanning-tree port
Correct Answer(s)
A. immediately loses its edge status
A. Becomes a normal spanning-tree portExplanation
When an RSTP edge port receives a BPDU, it immediately loses its edge status. This is because edge ports are designed to be connected to end devices that do not participate in spanning tree protocol. Receiving a BPDU indicates the presence of another bridge in the network, so the port can no longer be considered an edge port. Additionally, the edge port becomes a normal spanning-tree port, meaning it will start participating in the spanning tree protocol and forwarding BPDUs to other ports.Rate this question:
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- 5.
Refer to the exhibit. All switches in the network have empty MAC tables. STP has been disabled on the switches in the network. How will a broadcast frame that is sent by host PC1 be handled on the network?
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Switch SW1 will block the broadcast and drop the frame.
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Switch SW1 will forward the broadcast out all switch ports, except the originating port. This will generate an endless loop in the network.
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Switch SW1 will forward the broadcast out all switch ports, except the originating port. All hosts in the network will replay with a unicast frame sent to host PC1.
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Switch SW1 will forward the traffic out all switch ports except the originating port as a unicast frame. All hosts in the network will replay with a unicast frame sent to switch SW1.
Correct Answer
A. Switch SW1 will forward the broadcast out all switch ports, except the originating port. This will generate an endless loop in the network.Explanation
If STP (Spanning Tree Protocol) has been disabled on the switches in the network, switch SW1 will forward the broadcast frame out all switch ports, except the originating port. This will create an endless loop in the network because the broadcast frame will keep circulating through all the switches, continuously being forwarded out of all ports except the one it originated from. This can lead to network congestion and performance issues.Rate this question:
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- 6.
Which two items are true regarding the spanning-tree portfast command? (Choose two.)
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PortFast is Cisco proprietary.
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PortFast can negatively effect DHCP services.
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PortFast is used to more quickly prevent and eliminate bridging loops.
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Enabling PortFast on trunks that connect to other switches improves convergence.
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If an access port is configured with PortFast, it immediately transitions from a blocking to a forwarding state.
Correct Answer(s)
A. PortFast is Cisco proprietary.
A. If an access port is configured with PortFast, it immediately transitions from a blocking to a forwarding state.Explanation
PortFast is a Cisco proprietary feature that allows access ports to immediately transition from a blocking to a forwarding state, improving convergence. Enabling PortFast on trunks that connect to other switches does not improve convergence. PortFast can negatively affect DHCP services by allowing a host to bypass the DHCP process and obtain an IP address from a previous lease.Rate this question:
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- 7.
Refer to the exhibit. Server sends an ARP request for the MAC address of its default gateway. If STP is not enabled, what will be the result of this ARP request?
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Router_1 will drop the broadcast and reply with the MAC address of the next hop router.
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Switch_A will reply with the MAC address of the Router_1 E0 interface.
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Switch_A and Switch_B will continuously flood the message onto the network.
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The message will cycle around the network until its TTL is exceeded.
Correct Answer
A. Switch_A and Switch_B will continuously flood the message onto the network.Explanation
If STP (Spanning Tree Protocol) is not enabled, the result of the ARP request will be that Switch_A and Switch_B will continuously flood the message onto the network. This means that the ARP request will be broadcasted to all devices on the network, causing unnecessary traffic and potentially impacting network performance. Without STP to prevent loops in the network, the message will continue to circulate indefinitely until its time-to-live (TTL) value is exceeded.Rate this question:
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- 8.
What is the first step in the process of convergence in a spanning tree topology?
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Election of the root bridge
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Blocking of the non-designated ports
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Selection of the designated trunk port
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Determination of the designated port for each segment
Correct Answer
A. Election of the root bridgeExplanation
The first step in the process of convergence in a spanning tree topology is the election of the root bridge. The root bridge is the most important bridge in the network and serves as the reference point for all other bridges. It is elected based on a predetermined criteria such as the bridge with the lowest bridge ID. Once the root bridge is elected, the other bridges in the network will determine their roles and port states based on their distance to the root bridge. This process ensures that the network has a loop-free topology and allows for efficient forwarding of traffic.Rate this question:
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- 9.
How can a network administrator influence which STP switch becomes the root bridge?
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Configure all the interfaces on the switch as the static root ports.
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Change the BPDU to a lower value than that of the other switches in the network.
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Assign a lower IP address to the switch than that of the other switches in the network.
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Set the switch priority to a smaller value than that of the other switches in the network.
Correct Answer
A. Set the switch priority to a smaller value than that of the other switches in the network.Explanation
To influence which STP switch becomes the root bridge, the network administrator can set the switch priority to a smaller value than that of the other switches in the network. The switch with the lowest priority value will become the root bridge. By assigning a lower priority to a specific switch, the administrator can ensure that it becomes the root bridge and takes control of the STP topology. This allows for better control and management of the network.Rate this question:
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- 10.
Refer to the exhibit. The spanning-tree port priority of each interface is at the default setting. The network administrator enters the spanning-tree vlan 1 root primary command on S4. What is the effect of the command?
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Spanning tree blocks Gi 0/1 on S3.
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Gi 0/2 on S3 transitions to a root port.
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Port priority makes Gi 0/2 on S1 a root port.
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S4 is already the root bridge, so there are no port changes.
Correct Answer
A. Gi 0/2 on S3 transitions to a root port.Explanation
The command "spanning-tree vlan 1 root primary" on S4 will cause Gi 0/2 on S3 to transition to a root port. This command is used to configure a switch as the root bridge for a specific VLAN. By setting S4 as the root bridge for VLAN 1, it will have the lowest bridge ID and therefore all other switches in the network will adjust their port roles accordingly. In this case, S3's Gi 0/2 will become the root port, as it is the port that offers the lowest cost path to the root bridge (S4).Rate this question:
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- 11.
What two features of the Spanning-Tree Protocol contribute to the time it takes for a switched network to converge after a topology change occurs? (Choose two.)
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The max-age timer
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The spanning-tree hold down timer
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The forward delay
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the spanning-tree path cost
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The blocking delay
Correct Answer(s)
A. The max-age timer
A. The forward delayExplanation
The max-age timer and the forward delay are two features of the Spanning-Tree Protocol that contribute to the time it takes for a switched network to converge after a topology change occurs. The max-age timer is the maximum time a switch will wait to receive a hello message from its root bridge before considering the root bridge unavailable. This timer affects the convergence time as it determines how long a switch will wait before recalculating the spanning-tree topology. The forward delay is the time a switch waits before transitioning a port from the blocking state to the forwarding state. This delay allows for stability in the network by ensuring that all switches have updated their forwarding tables before allowing traffic to flow through the newly designated forwarding ports.Rate this question:
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- 12.
In which STP state does a port record MAC addresses but not forward user data?
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Blocking
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Learning
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Disabling
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Listening
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Forwarding
Correct Answer
A. LearningExplanation
In the learning state of STP (Spanning Tree Protocol), a port records MAC addresses but does not forward user data. This state allows the switch to learn the MAC addresses of devices connected to the port by receiving and processing incoming frames. However, it does not yet participate in forwarding user data until it transitions to the forwarding state.Rate this question:
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- 13.
Which three statements are accurate regarding RSTP and STP? (Choose three.)
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RSTP uses a faster algorithm to determine root ports.
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Both RSTP and STP use the portfast command to allow ports to immediately transition to forwarding state.
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Like STP PortFast, an RSTP edge port that receives a BPDU loses its edge port status immediately and becomes a normal spanning-tree port.
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Configuration commands to establish primary and secondary root bridges are identical for STP and RSTP.
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Because of the format of the BPDU packet, RSTP is backward compatible with STP.
Correct Answer(s)
A. Both RSTP and STP use the portfast command to allow ports to immediately transition to forwarding state.
A. Configuration commands to establish primary and secondary root bridges are identical for STP and RSTP.
A. Because of the format of the BPDU packet, RSTP is backward compatible with STP.Explanation
RSTP and STP both use the portfast command to allow ports to immediately transition to the forwarding state. This means that when a port is enabled with portfast, it will skip the listening and learning states and go directly to forwarding, reducing the convergence time. The configuration commands to establish primary and secondary root bridges are also the same for both STP and RSTP. This allows for a seamless transition between the two protocols. Additionally, RSTP is backward compatible with STP due to the format of the BPDU packet, meaning that RSTP can coexist with STP in the same network without causing any compatibility issues.Rate this question:
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- 14.
What two elements will exist in a converged network with one spanning tree? (Choose two.)
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One root bridge per network
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All non-designated ports forwarding
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One root port per non-root bridge
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Multiple designated ports per segment
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One designated port per network
Correct Answer(s)
A. One root bridge per network
A. One root port per non-root bridgeExplanation
In a converged network with one spanning tree, there will be one root bridge per network. The root bridge is the central bridge that is responsible for making forwarding decisions in the network. Additionally, there will be one root port per non-root bridge. The root port is the port on a non-root bridge that has the best path to the root bridge. This port is responsible for forwarding traffic towards the root bridge.Rate this question:
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- 15.
Which statement or set of paired statements correctly compares STP with RSTP?
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STP and RSTP use the same BPDU format.
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STP specifies backup ports. RSTP has only root ports, alternate ports, and designated ports.
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STP port states are independent of port roles. RSTP ties together the port state and port role.
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STP waits for the network to converge before placing ports into forwarding state. RSTP places alternate ports into forwarding state immediately.
Correct Answer
A. STP waits for the network to converge before placing ports into forwarding state. RSTP places alternate ports into forwarding state immediately.Explanation
STP and RSTP are both spanning tree protocols used to prevent loops in network topologies. The correct answer explains that one key difference between the two is their behavior when it comes to placing ports into forwarding state. STP waits for the network to converge before allowing ports to forward traffic, while RSTP immediately places alternate ports into forwarding state. This means that RSTP can provide faster convergence and reduce network downtime compared to STP.Rate this question:
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- 16.
Refer to the exhibit. What can be determined from the output shown?
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Two hosts communicating between ports Fa 0/2 and Fa 0/4 have a cost of 38.
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The priority was statically configured to identify the root.
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STP is disabled on this switch.
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The timers have been altered to reduce convergence time.
Correct Answer
A. The priority was statically configured to identify the root.Explanation
The output shown indicates that the priority was statically configured to identify the root. This means that the switch has been manually configured to have a higher priority value, making it more likely to become the root switch in the spanning tree. This can be determined because the output does not mention any other factors that could affect the root selection process, such as STP being disabled or timers being altered.Rate this question:
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- 17.
Which two criteria does a switch use to select the root bridge? (Choose two.)
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Bridge priority
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Switching speed
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number of ports
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Base MAC address
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Memory size
Correct Answer(s)
A. Bridge priority
A. Base MAC addressExplanation
A switch uses two criteria to select the root bridge: bridge priority and base MAC address. The bridge priority is a numerical value that determines the likelihood of a switch becoming the root bridge. The switch with the lowest bridge priority will become the root bridge. The base MAC address is used as a tiebreaker if multiple switches have the same bridge priority. The switch with the lowest base MAC address will become the root bridge.Rate this question:
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- 18.
What three link types have been defined for Rapid Spanning-Tree Protocol? (Choose three.)
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Shared
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End-to-end
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Edge-type
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Boundary-type
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Point-to-point
Correct Answer(s)
A. Shared
A. Edge-type
A. Point-to-pointExplanation
The three link types that have been defined for Rapid Spanning-Tree Protocol are shared, edge-type, and point-to-point. The shared link type refers to a link that is shared among multiple devices. The edge-type link refers to a link that is connected to an end device. The point-to-point link refers to a link that is directly connected between two devices.Rate this question:
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- 19.
What Rapid Spanning Tree Protocol (RSTP) role is assigned to the forwarding port elected for every switched Ethernet LAN segment?
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Alternate
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Backup
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Designated
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Root
Correct Answer
A. DesignatedExplanation
The Designated role is assigned to the forwarding port elected for every switched Ethernet LAN segment in Rapid Spanning Tree Protocol (RSTP). The Designated port is responsible for forwarding data on its respective LAN segment and is selected based on the lowest path cost to the root bridge. It is the port that provides the best path to reach the root bridge and ensures efficient and reliable communication within the LAN.Rate this question:
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- 20.
When PVST+ was developed, the Bridge ID was modified to include which information?
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Bridge priority
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MAC address
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Protocol
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VLAN ID
Correct Answer
A. VLAN IDExplanation
When PVST+ was developed, the Bridge ID was modified to include the VLAN ID information. The Bridge ID is a unique identifier used in Spanning Tree Protocol (STP) to determine the root bridge and the path cost to reach it. By including the VLAN ID in the Bridge ID, PVST+ allows for separate spanning trees to be maintained for each VLAN in a network. This ensures that each VLAN has its own root bridge and path cost calculation, improving network efficiency and reducing the risk of loops.Rate this question:
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Current Version
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Mar 22, 2023Quiz Edited by
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Feb 02, 2010Quiz Created by
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