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Network Access

400 questions

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Question 221Question →

An administrator is configuring edge interfaces on a Cisco Catalyst switch connected directly to end-user host computers. Which two operational characteristics or benefits occur when Cisco PortFast is enabled on these access ports?

Select all that apply

Show answer & explanation

Answer: The interface transitions immediately to the Forwarding state by bypassing the Listening and Learning states.; The switch prevents Topology Change Notifications (TCNs) from being generated when the link state on the port toggles.

Answer

PortFast allows access interfaces connected to host devices to bypass Listening and Learning states to transition immediately into Forwarding, and suppresses Topology Change Notifications (TCNs) when host links change state.
Enabling PortFast on an access port allows host devices to bypass the standard 802.1D Listening and Learning states (saving 30 seconds) and enter the Forwarding state immediately upon link initialization. Furthermore, because end hosts frequently turn on and off, PortFast suppresses Topology Change Notifications (TCNs) for those ports, preventing unnecessary MAC address table aging across the switch network.

Step-by-Step Solution

1
Identify the primary operational function of Cisco STP PortFast on access ports.
PortFast allows an edge interface to skip the traditional 802.1D Listening (15s) and Learning (15s) states, placing the port immediately into the Forwarding state upon link up.
End-user workstations do not create Layer 2 loops, so waiting for standard convergence timers is unnecessary and can cause application timeouts (such as DHCP).
2
Identify the network-wide benefit regarding Spanning Tree topology notifications.
The switch does not generate Topology Change Notifications (TCNs) when a PortFast-enabled port goes up or down.
Preventing TCN generation for simple workstation reboots avoids constantly flushing MAC address tables on all switches across the Layer 2 domain.

Key Concept

Cisco STP PortFast operation and benefits on edge access ports
Question 222Question →

A network administrator manually configures a switch running Rapid PVST+ with a base bridge priority of 28672 for VLAN 100. What total priority value will be transmitted in the Bridge Identifier (BID) within BPDUs generated for VLAN 100 on this switch?

Show answer & explanation

Answer: 28772

Answer

28772 is the total bridge priority advertised in the BPDUs for VLAN 100 because Rapid PVST+ adds the VLAN ID (100) to the configured base bridge priority (28672).
In Rapid PVST+, Cisco switches append the 12-bit VLAN ID (System ID Extension) to the 4-bit configurable base priority. Adding the VLAN ID of 100 to the base priority of 28672 yields a total priority value of 28772.

Step-by-Step Solution

1
Identify the base bridge priority and the VLAN ID.
Base priority is 28672 and VLAN ID is 100.
Rapid PVST+ uses the 802.1t System ID Extension mechanism.
2
Calculate total priority by adding the System ID Extension (VLAN ID) to the base priority.
28672+100=2877228672 + 100 = 28772
The 16-bit Priority field in the BID consists of a 4-bit Priority field (multiples of 4096) and a 12-bit System ID Extension field.

Key Concept

Rapid PVST+ System ID Extension and Bridge Identifier (BID) Calculation
Estimated Time:45s
Question 223Question →

An administrator executes the following command on a Cisco Catalyst switch port connected to an unmanaged access switch:

`Switch(config-if)# spanning-tree portfast`

Shortly after, a transient Layer 2 loop brings down the network segment before STP can converge. Which operational characteristic of Cisco PortFast directly allowed this loop to form?

Show answer & explanation

Answer: PortFast transitions the interface immediately from Blocking to Forwarding, bypassing the Listening and Learning states that normally detect loops.

Answer

PortFast transitions the interface immediately from Blocking to Forwarding, bypassing the Listening and Learning states that normally detect loops.
Enabling PortFast on an access port allows it to immediately transition from Blocking directly into the Forwarding state, bypassing the 15-second Listening state and 15-second Learning state. When connected to another switch (even an unmanaged one), this immediate transition to Forwarding creates a transient or permanent Layer 2 loop before STP has the chance to listen for BPDUs and move redundant ports into the Blocking state.

Step-by-Step Solution

1
Analyze standard 802.1D STP state transitions for a newly connected link.
Standard ports move through Blocking → Listening (15 seconds) → Learning (15 seconds) → Forwarding (total delay of 30 seconds).
The Listening and Learning states allow the switch to receive BPDUs and build MAC address tables to detect potential loops before user traffic is forwarded.
2
Evaluate the behavior of enabling PortFast on an interface.
PortFast skips Listening and Learning, bringing the interface directly into the Forwarding state upon link-up.
This is intended for edge end-user devices (workstations, printers) that cannot cause Layer 2 loops.
3
Determine the impact of enabling PortFast on a switch-to-switch link (or link connected to an unmanaged switch).
Because the port immediately enters Forwarding state, broadcast traffic and loops occur instantly before BPDUs can be evaluated to block the redundant path.
Misapplying PortFast on non-edge ports bypasses loop-prevention safeguards.

Key Concept

Cisco PortFast operational mechanism and misconfiguration risks on switch interconnects.
Question 224Question →

A network administrator is connecting Switch-1 and Switch-2 using a dual-link EtherChannel across GigabitEthernet0/1 and GigabitEthernet0/2 interfaces. On Switch-1, the member interfaces are configured with `channel-group 10 mode active`. What will happen if the corresponding physical interfaces on Switch-2 are configured with `channel-group 10 mode passive`?

Show answer & explanation

Answer: The EtherChannel bundle will successfully form because active mode actively initiates LACP negotiation while passive mode responds to incoming LACP packets.

Answer

The EtherChannel bundle will successfully form because active mode actively initiates LACP negotiation while passive mode responds to incoming LACP packets.
Link Aggregation Control Protocol (IEEE 802.3ad / 802.1AX) uses active and passive negotiation modes. The active keyword causes the switch port to actively initiate negotiation by transmitting LACP packets. The passive keyword configures the port to respond to received LACP packets without sending them unprompted. Therefore, combining an active port on one side with a passive port on the other side successfully forms an EtherChannel.

Step-by-Step Solution

1
Analyze Switch-1's LACP mode configuration.
Switch-1 is set to 'active', meaning it sends LACP frames out of the interfaces to negotiate the bundle.
LACP active mode actively initiates link aggregation negotiations.
2
Analyze Switch-2's LACP mode configuration.
Switch-2 is set to 'passive', meaning it does not initiate LACP negotiation but responds when it receives LACP frames.
LACP passive mode listlessly waits for received LACP packets before forming an EtherChannel.
3
Determine the resulting channel negotiation status.
Active mode sends LACP frames, passive mode receives and responds to them, allowing the bundle to successfully form.
Active-to-Active and Active-to-Passive combinations establish LACP EtherChannels, whereas Passive-to-Passive fails.

Key Concept

LACP EtherChannel Negotiation Modes (Active and Passive)
Estimated Time:1m 30s
Question 225Question →

A network engineer must manually configure a routed (Layer 3) Link Aggregation Control Protocol (LACP) EtherChannel bundle on a Cisco Catalyst switch using physical member interfaces GigabitEthernet1/0/1 and GigabitEthernet1/0/2. The EtherChannel must use Port-channel 20 and be configured with IP address 10.20.20.1/30. Arrange the CLI configuration commands into the correct execution sequence from top to bottom.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct CLI sequence is: 1) interface range GigabitEthernet1/0/1 - 2, 2) no switchport, 3) channel-group 20 mode active, 4) interface Port-channel 20, and 5) ip address 10.20.20.1 255.255.255.252.
To successfully deploy a routed (Layer 3) LACP EtherChannel, physical interfaces must first be selected, configured with 'no switchport' to disable Layer 2 switching, and bound to a channel group using an active LACP mode. Afterwards, the administrator enters the logical port-channel interface context to configure the IP address parameters.

Step-by-Step Solution

1
Select physical member interfaces
Enters interface range configuration mode for GigabitEthernet1/0/1 and GigabitEthernet1/0/2.
Configuration must start at physical interfaces to prepare them before bundling.
2
Convert physical interfaces to Layer 3 routed interfaces
Disables Layer 2 switching capabilities on physical member ports.
Physical member ports of a routed EtherChannel must have 'no switchport' applied before participating in a Layer 3 channel group.
3
Assign interfaces to an active LACP channel group
Creates Port-channel 20 automatically and sets LACP mode to active.
The 'mode active' parameter enables LACP dynamic negotiation on the physical member interfaces.
4
Select logical Port-channel interface
Enters interface configuration mode for Port-channel 20.
Network configuration, including IP addressing, must be applied directly to the logical port-channel container.
5
Configure IP address on Port-channel interface
Assigns IPv4 address 10.20.20.1/30 to Port-channel 20.
Layer 3 EtherChannels hold IP addressing at the port-channel level rather than individual member links.

Key Concept

Layer 3 EtherChannel (LACP) Configuration Sequence
Question 226Question →

Which IEEE 802.1D Spanning Tree Protocol (STP) port state populates the switch MAC address table using source MAC addresses of received frames, but does not yet forward user data frames?

Show answer & explanation

Answer: Learning

Answer

Learning
Under legacy 802.1D Spanning Tree Protocol, the Learning state acts as a transition phase between Listening and Forwarding. During this state, the switch port receives data frames and inspects source MAC addresses to populate its address table, but it continues to drop data traffic to maintain a loop-free environment.

Step-by-Step Solution

1
Analyze the operational requirements stated in the prompt.
The port state must populate the MAC address table based on incoming frame headers while continuing to discard user data frames.
Building the MAC address table before enabling full data transfer minimizes initial unicast flooding once data forwarding begins.
2
Evaluate the 802.1D STP port states against these requirements.
Blocking discards user data and does not learn MAC addresses. Listening evaluates network topology BPDUs without learning MAC addresses. Learning populates the MAC table but discards data frames. Forwarding both populates MAC tables and forwards data frames.
Only the Learning state satisfies the specific condition of MAC learning without data forwarding.

Key Concept

STP 802.1D Port States and Functions
Question 227Question →

A network technician is provisioning interface FastEthernet 0/1 for a newly attached workstation. Which two Cisco IOS commands must be executed in interface configuration mode to manually set the port as a static access interface assigned to VLAN 20? (Select two.)

Select all that apply

Show answer & explanation

Answer: switchport mode access; switchport access vlan 20

Answer

The two required interface configuration commands are 'switchport mode access' and 'switchport access vlan 20'.
To complete access port configuration, the command 'switchport mode access' sets the administrative mode to access, while 'switchport access vlan 20' binds the port to the specific VLAN ID.

Step-by-Step Solution

1
Set the port mode
Interface is forced into access mode using 'switchport mode access'
Ensures DTP negotiation does not convert the port into a trunk link
2
Assign the VLAN membership
Interface is assigned to VLAN 20 using 'switchport access vlan 20'
Maps untagged frames received on this interface to broadcast domain 20

Key Concept

Access Port VLAN Configuration Syntax
Question 228Question →

A switch port running classic IEEE 802.1D Spanning Tree Protocol (STP) detects link UP on a non-PortFast access interface. Place the 802.1D STP port states in the exact chronological sequence through which the interface transitions from link initialization to fully active frame processing.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct operational sequence of classic 802.1D STP port states from link bring-up to active data transmission is: Blocking State -> Listening State -> Learning State -> Forwarding State.
Under standard IEEE 802.1D Spanning Tree Protocol, non-PortFast interfaces progress strictly through Blocking, Listening, Learning, and Forwarding states. The Blocking state prevents loops upon initialization; Listening (15s Forward Delay) processes BPDUs and determines port roles; Learning (15s Forward Delay) builds MAC address tables from source MACs; and Forwarding permits normal data payload processing.

Step-by-Step Solution

1
Identify the initial non-functional state upon physical link activation.
The port initializes in the Blocking State.
STP ports default to Blocking to discard user data frames and prevent switching loops while listening for control frames (BPDUs).
2
Identify the state where STP role determination occurs.
The port moves into the Listening State.
During the Listening phase (lasting 15 seconds by default), the switch processes and sends BPDUs to determine Root Bridge and port roles without populating MAC tables or forwarding data frames.
3
Identify the state where address table construction begins.
The port transitions to the Learning State.
After the first 15-second Forward Delay timer expires, the port enters Learning where it examines source MAC addresses of incoming frames to build the MAC address table, but still drops payload data frames.
4
Identify the final fully functional state.
The port enters the Forwarding State.
After the second 15-second Forward Delay timer expires (total 30 seconds convergence), the port transitions to Forwarding where it actively forwards and receives user data frames.

Key Concept

IEEE 802.1D STP Sequential Port State Transitions
Estimated Time:1m 15s
Question 229Question →

A network administrator is deploying a dynamic Layer 2 EtherChannel using the Link Aggregation Control Protocol (LACP) between Switch-A and Switch-B across two physical interfaces. Switch-A must actively initiate channel negotiation, whereas Switch-B must only listen and respond to incoming LACP negotiation requests.

Which two configuration statements correctly describe the settings required to establish this EtherChannel bundle? (Select two.)

Select all that apply

Show answer & explanation

Answer: Switch-A member interfaces must be configured with channel-group 1 mode active.; Switch-B member interfaces must be configured with channel-group 1 mode passive.

Answer

To form an LACP EtherChannel where one switch actively initiates negotiation and the other responds, Switch-A member interfaces must be configured with 'channel-group 1 mode active' and Switch-B member interfaces must be configured with 'channel-group 1 mode passive'.
In LACP dynamic EtherChannel configuration, 'active' mode initiates LACP negotiations by sending LACP frames, while 'passive' mode responds to incoming LACP negotiation frames without sending them unprompted. An active-to-passive pairing successfully establishes the EtherChannel bundle.

Step-by-Step Solution

1
Analyze protocol negotiation requirements for LACP.
LACP supports two modes: active (initiates negotiation) and passive (responds to negotiation).
Switch-A must initiate negotiation, so it requires active mode. Switch-B must only respond, so it requires passive mode.
2
Evaluate protocol compatibility.
PAgP modes (desirable, auto) cannot pair with LACP modes (active, passive).
Configuring desirable mode on Switch-B attempts PAgP negotiation, causing negotiation failure with an LACP active switch.
3
Verify physical interface parameter consistency requirements.
All interfaces bundled into an EtherChannel on a local switch must share identical settings.
Mismatched native VLANs or trunk settings across member links on the same switch prevent the EtherChannel from bundling successfully.

Key Concept

LACP EtherChannel Mode Compatibility and Member Port Prerequisites
Question 230Question →

An administrator notices CDP log messages indicating a native VLAN mismatch on an 802.1Q trunk link between two switches. Switch-1 is configured with native VLAN 99 on interface GigabitEthernet0/1, while Switch-2 uses the default native VLAN 1 on interface GigabitEthernet0/1. If a host in VLAN 99 on Switch-1 transmits untagged frames across the trunk link, how will Switch-2 process this traffic?

Show answer & explanation

Answer: Switch-2 receives the untagged frames and forwards them into VLAN 1, leading to cross-VLAN traffic leakage.

Answer

Switch-2 receives the untagged frames and forwards them into VLAN 1, leading to cross-VLAN traffic leakage.
Under IEEE 802.1Q trunking rules, frames belonging to the native VLAN are sent untagged across the link. When a receiving switch receives untagged frames, it automatically maps them to its own configured native VLAN. Consequently, traffic originating from VLAN 99 on Switch-1 will be placed into VLAN 1 on Switch-2, resulting in unintended cross-VLAN traffic leakage.

Step-by-Step Solution

1
Analyze how 802.1Q handles native VLAN traffic.
Frames assigned to the native VLAN of a trunk interface are transmitted across the physical link without an added 802.1Q 4-byte header tag.
802.1Q trunking specifies that native VLAN traffic remains untagged for backward compatibility with legacy non-trunking devices.
2
Evaluate the behavior of the receiving switch when native VLAN settings are mismatched.
Switch-2 receives untagged frames from Switch-1 (sent from VLAN 99) and places them into Switch-2's configured native VLAN (VLAN 1).
A receiving switch maps any incoming untagged frame directly to its own configured native VLAN.
3
Determine the operational security and switching impact.
Traffic leaks across VLAN boundaries between VLAN 99 on Switch-1 and VLAN 1 on Switch-2, creating a security risk and potential connectivity issues.
Mismatching native VLANs breaks VLAN isolation for untagged traffic without bringing the physical link down.

Key Concept

802.1Q Native VLAN Tagging Mechanics and Traffic Leakage
Question 231Question →

A network administrator is inspecting a port configuration on a Cisco Catalyst switch after connecting an end-host workstation. The output of the command `show interfaces fastethernet 0/15 switchport` displays the following information:

text
Name: Fa0/15
Administrative Mode: dynamic auto
Operational Mode: static access
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: native
Negotiation of Trunking: On
Access Mode VLAN: 20 (VLAN0020)
Trunking Native Mode VLAN: 1 (default)

Which statement correctly explains why the operational mode of interface FastEthernet 0/15 is reported as `static access`?

Show answer & explanation

Answer: The connected end-host does not send Dynamic Trunking Protocol (DTP) negotiation frames, so the port defaults to operating as an access port in VLAN 20.

Answer

The connected end-host does not send Dynamic Trunking Protocol (DTP) negotiation frames, so the port defaults to operating as an access port in VLAN 20.
The Administrative Mode of FastEthernet 0/15 is `dynamic auto`, meaning the interface is capable of becoming a trunk if the neighboring device actively requests it (such as a port in `dynamic desirable` or `trunk` mode). Because an end-host workstation does not run Dynamic Trunking Protocol (DTP), no DTP frames are received. Consequently, the interface defaults to functioning as a single-VLAN access port assigned to Access Mode VLAN 20.

Step-by-Step Solution

1
Analyze the Administrative Mode and Operational Mode from the CLI output.
Administrative Mode is `dynamic auto` and Operational Mode is `static access`.
Administrative Mode indicates how the port is configured to negotiate, while Operational Mode shows its actual behavior.
2
Evaluate DTP behavior in `dynamic auto` mode.
Ports set to `dynamic auto` respond to DTP negotiation (desirable or trunk) but will not initiate DTP packets to form a trunk.
Since the end device is a host workstation, no DTP packets are received by the switch port.
3
Determine the operational state and active VLAN.
Failing to form a trunk link causes the switch port to fall back to access mode, assigning untagged host traffic to Access Mode VLAN 20.
An un-negotiated dynamic switchport defaults to an access port carrying traffic for its configured access VLAN.

Key Concept

DTP Negotiation Mechanics and Access Port Operational States
Question 232Question →

An enterprise network topology running Rapid PVST+ consists of three switches: Switch-1, Switch-2, and Switch-3.

- Switch-1 is configured as the Root Bridge for VLAN 20 with a priority of 4096.
- Switch-2 connects to Switch-1 via a 10 Gigabit Ethernet link (10 Gbps10\text{ Gbps}, STP cost = 2).
- Switch-3 connects directly to Switch-1 via a 1 Gigabit Ethernet link (Gi0/1, STP cost = 4).
- Switch-3 also connects to Switch-2 via two parallel 1 Gigabit Ethernet links: Gi0/2 (connected to Switch-2 Gi0/1) and Gi0/3 (connected to Switch-2 Gi0/2).
- All interface STP costs and port priorities use default Cisco values.

Which port role and operational state will interface Gi0/2 on Switch-3 assume for VLAN 20?

Show answer & explanation

Answer: Alternate port role in the Discarding state

Answer

Interface Gi0/2 on Switch-3 assumes the Alternate port role in the Discarding state.
Switch-3 evaluates all available paths to Root Bridge Switch-1. The direct 1 Gbps link on interface Gi0/1 provides a path cost of 4, whereas traversing Switch-2 via interface Gi0/2 yields a path cost of 6 (cost 2 from Switch-2 to Switch-1 plus cost 4 from Switch-3 to Switch-2). Consequently, Gi0/1 is elected as Switch-3's Root Port. On the segments connecting Switch-2 and Switch-3, Switch-2 advertises a lower root path cost (2) than Switch-3 (4), electing Switch-2 as the designated bridge. Interface Gi0/2 on Switch-3 receives BPDUs from Switch-2 and is designated as an Alternate port in the Discarding state.

Step-by-Step Solution

1
Determine the Root Bridge for VLAN 20
Switch-1 is the Root Bridge due to its configured priority of 4096.
The switch with the lowest Bridge ID (Priority + System ID Extension + MAC) becomes the Root Bridge.
2
Calculate cumulative path costs from Switch-3 to the Root Bridge
Direct path via Gi0/1 = 4. Path via Switch-2 (Gi0/2 or Gi0/3) = 2 (Switch-2 to Switch-1) + 4 (Switch-3 to Switch-2) = 6.
Standard Rapid PVST+ path cost for 10 Gbps10\text{ Gbps} is 2 and for 1 Gbps1\text{ Gbps} is 4.
3
Select Switch-3's Root Port
Gi0/1 is selected as the Root Port on Switch-3 and transitions to the Forwarding state.
The interface with the lowest cumulative path cost to the Root Bridge is elected as the Root Port.
4
Determine port roles for Switch-3's remaining interfaces (Gi0/2 and Gi0/3)
Switch-2's root path cost (2) is less than Switch-3's root path cost (4), making Switch-2 the Designated Bridge on the inter-switch links between Switch-2 and Switch-3. Gi0/2 on Switch-3 receives superior BPDUs from Switch-2 and is placed into the Alternate role in the Discarding state.
Non-root ports receiving superior BPDUs from another switch become Alternate ports in Discarding state under Rapid PVST+.

Key Concept

Rapid PVST+ Root Port and Alternate Port election rules based on cumulative root path costs and designated bridge tie-breakers.
Question 233Question →

Match each Cisco Wireless LAN Controller (WLC) physical or logical interface to its primary operational role and management connectivity requirement.

Click a left item, then click its matching right item

Items

Service Port Interface
Management Interface
Virtual Interface
Dynamic Interface

Matches

Show answer & explanation

Answer

Service Port Interface pairs with out-of-band management over a separate routing table. Management Interface pairs with in-band WLC administration, CAPWAP tunnel termination, and RADIUS. Virtual Interface pairs with web authentication redirection, DHCP relay proxying, and mobility. Dynamic Interface pairs with mapping WLAN SSIDs to 802.1Q VLAN trunks.
Each Cisco WLC interface has a distinct role: Service Port provides out-of-band access via an isolated routing table; Management Interface manages in-band CAPWAP tunnels, GUI/SSH access, and AAA; Virtual Interface handles web authentication redirects using a non-routable IP address; and Dynamic Interfaces map SSIDs to enterprise switchport VLANs.

Step-by-Step Solution

1
Identify out-of-band management capabilities
Match Service Port Interface to out-of-band access
The Service Port is physically separated from data ports and resides in an isolated management network routing table.
2
Identify in-band controller administration and AP CAPWAP termination interface
Match Management Interface to in-band administrative operations and CAPWAP tunnel endpoint functions
Lightweight APs discover and establish CAPWAP management tunnels to the controller's Management Interface IP address.
3
Determine the interface responsible for web redirection and mobility signaling
Match Virtual Interface to web auth redirection and relay proxying
The Virtual Interface uses an internal non-routable IP address to handle Layer 3 guest web portal redirects.
4
Identify data plane mapping for wireless client payload traffic
Match Dynamic Interface to SSID-to-VLAN trunk mapping
Dynamic interfaces bind configured WLANs to specific 802.1Q VLAN tags on distribution switchports.

Key Concept

Cisco WLC Logical and Physical Interface Roles for In-Band and Out-Of-Band Management
Question 234Question →

A network administrator needs to manually configure the base bridge priority for VLAN 30 on a Cisco Catalyst switch running Rapid PVST+. Which configured base priority value is valid and will be accepted by Cisco IOS?

Show answer & explanation

Answer: 4096

Answer

4096 is a valid base priority because Rapid PVST+ requires bridge priority values to be configured in increments of 4096.
In Rapid PVST+, the 16-bit Priority field is divided into a 4-bit base priority field and a 12-bit System ID Extension field (which carries the VLAN ID). Because only 4 bits are used for the base priority, configurable values must be increments of 40964096 (such as 0,4096,8192,122880, 4096, 8192, 12288, etc.). Selecting 4096 provides a valid base priority value.

Step-by-Step Solution

1
Identify the STP bridge priority configuration requirement for Rapid PVST+.
Bridge priority values must be configured in multiples of 4096 due to the 12-bit System ID Extension field in the 802.1t bridge ID structure.
Cisco IOS reserves 12 bits for the VLAN ID (System ID Extension) within the 16-bit Priority field, leaving 4 bits for the base priority.
2
Evaluate the given options to find a valid multiple of 4096.
4096 is equal to 4096×14096 \times 1, making it a valid configurable base priority value.
Values such as 3000, 4000, and 4126 are not valid base priority multiples.

Key Concept

Rapid PVST+ Bridge Priority and System ID Extension
Question 235Question →

Four Cisco switches (SW1, SW2, SW3, and SW4) are interconnected in a enterprise mesh topology running Rapid PVST+ for VLAN 10. The bridge priorities (base priority values) and MAC addresses for VLAN 10 are configured as follows:

SwitchBase Bridge PriorityMAC Address
SW140960001.AAAA.AAAA
SW2286720002.BBBB.BBBB
SW3327680003.CCCC.CCCC
SW4327680004.DDDD.DDDD

The inter-switch physical links and operational speeds are configured as follows:
- SW1 Gi0/1 <--> SW2 Gi0/1 (1 Gbps)
- SW1 Gi0/2 <--> SW3 Gi0/1 (1 Gbps)
- SW2 Gi0/2 <--> SW4 Gi0/1 (1 Gbps)
- SW2 Gi0/3 <--> SW3 Gi0/2 (100 Mbps)
- SW3 Gi0/3 <--> SW4 Gi0/2 (1 Gbps)

All switch ports use default Rapid PVST+ 802.1w short path costs. Which spanning-tree port role and operational state will interface Gi0/2 on SW4 assume for VLAN 10?

Show answer & explanation

Answer: Alternate port in the Discarding state

Answer

Alternate port in the Discarding state
SW1 is the Root Bridge because it has the lowest Bridge ID (4106:0001.AAAA.AAAA). Both SW2 and SW3 elect their direct 1 Gbps connections to SW1 as Root Ports, giving both switches a Root Path Cost of 4. SW4 has two 1 Gbps paths to the root: via SW2 (cost 4 + 4 = 8) and via SW3 (cost 4 + 4 = 8). Because the path costs are tied at 8, SW4 breaks the tie using the lowest upstream Designated Bridge ID. SW2's Bridge ID (28682:0002.BBBB.BBBB) is lower than SW3's Bridge ID (32778:0003.CCCC.CCCC), so SW4 selects Gi0/1 as its Root Port. On the link between SW3 Gi0/3 and SW4 Gi0/2, SW3 advertises a lower Root Path Cost (4) than SW4 (8). Thus, SW3 Gi0/3 becomes the Designated Port for the segment, and SW4 Gi0/2 transitions to an Alternate port role in the Discarding state.

Step-by-Step Solution

1
Determine the Root Bridge for VLAN 10.
SW1 total priority = 4096+10=41064096 + 10 = 4106. Since 41064106 is the lowest bridge priority in the network, SW1 becomes the Root Bridge.
Rapid PVST+ adds the VLAN ID (1010) to the base priority to form the total Bridge Priority.
2
Calculate Root Path Costs for SW2 and SW3.
SW2 Root Port = Gi0/1 (Cost 44). SW3 Root Port = Gi0/1 (Cost 44).
1 Gbps link cost under default short path cost mode is 44.
3
Evaluate SW4 Root Port election between Gi0/1 and Gi0/2.
Path via Gi0/1 (SW2): Cumulative cost =4+4=8= 4 + 4 = 8. Designated Bridge ID =28682:0002.BBBB.BBBB= 28682:0002.BBBB.BBBB.
Path via Gi0/2 (SW3): Cumulative cost =4+4=8= 4 + 4 = 8. Designated Bridge ID =32778:0003.CCCC.CCCC= 32778:0003.CCCC.CCCC.
SW4 chooses Gi0/1 as its Root Port (Forwarding state) because SW2 has a lower Bridge ID than SW3.
When cumulative path costs are tied, the upstream Designated Bridge ID breaks the tie.
4
Determine Designated Port and Alternate Port roles on the link between SW3 Gi0/3 and SW4 Gi0/2.
SW3 advertises Root Path Cost 44 on Gi0/3. SW4 advertises Root Path Cost 88 on Gi0/2. SW3 wins Designated Port role (Forwarding state). SW4 Gi0/2 becomes an Alternate Port in the Discarding state.
The bridge advertising the lower cumulative Root Path Cost on a segment becomes the Designated Bridge for that link.

Key Concept

Rapid PVST+ Port Role Election and State Transitions
Question 236Question →

A network administrator needs to explicitly configure interface GigabitEthernet1/0/12 to function strictly as a non-trunking Layer 2 access port on a Cisco Catalyst switch. Which Cisco IOS command must be entered in interface configuration mode to achieve this?

Show answer & explanation

Answer: switchport mode access

Answer

The command 'switchport mode access' explicitly configures an interface to operate as a static Layer 2 access port.
The command 'switchport mode access' configures the switch interface to operate purely as an access port, ensuring it handles untagged traffic for a single VLAN and does not form a trunk link with attached devices.

Step-by-Step Solution

1
Identify the requirement
The port must be configured strictly as a static access port (non-trunking).
By default, Cisco switch ports may negotiate trunking via Dynamic Trunking Protocol (DTP).
2
Select the correct Cisco IOS CLI command for setting the operational mode
Use 'switchport mode access'.
Executing 'switchport mode access' under interface configuration mode locks the interface into access mode and prevents trunk formation.

Key Concept

Access Port Interface Mode Configuration
Question 237Question →

An administrator issues the command `show spanning-tree interface gigabitethernet 0/1` on a Cisco Catalyst switch connected to a workstation. The command output indicates that the port is in the `FWD` state and lists `P2p Edge` under the Type column. Which operational behavior is directly associated with this interface status?

Show answer & explanation

Answer: The interface immediately transitions to the forwarding state upon linkup by bypassing the listening and learning states.

Answer

The interface immediately transitions to the forwarding state upon linkup by bypassing the listening and learning states.
When an interface is designated as an Edge port (PortFast enabled), it transitions directly to the forwarding state upon link activation. This bypasses the listening and learning states, preventing convergence delays for end-user workstations.

Step-by-Step Solution

1
Interpret the CLI output port type
The `P2p Edge` designation indicates that Cisco PortFast is enabled on a point-to-point link connected to an end device.
Edge ports in Spanning Tree Protocol represent host-facing connections that do not lead to another switch.
2
Identify the functional mechanism of PortFast
PortFast bypasses the 802.1D Listening (15s) and Learning (15s) states, placing the interface into Forwarding immediately upon link UP.
This allows hosts to quickly obtain IP address assignments via DHCP without timing out during boot.

Key Concept

PortFast / Edge Port State Transition and Convergence Mechanics
Question 238Question →

A network administrator is configuring a routed (Layer 3) EtherChannel bundle using LACP on a Cisco Catalyst switch. The administrator creates the logical interface using `interface Port-channel 10`, executes `no switchport`, and assigns an IPv4 address. Next, the administrator enters interface configuration mode for GigabitEthernet0/1, GigabitEthernet0/2, and GigabitEthernet0/3. On GigabitEthernet0/1 and GigabitEthernet0/2, the administrator issues `no switchport` followed by `channel-group 10 mode active`. However, on interface GigabitEthernet0/3, the administrator issues `channel-group 10 mode active` without first executing `no switchport`.

What is the resulting operational status of interface GigabitEthernet0/3 in the output of `show etherchannel summary`?

Show answer & explanation

Answer: It remains in an independent (I) state and fails to bundle because its Layer 2 switchport mode does not match the Layer 3 configuration of the Port-Channel.

Answer

The interface remains in an independent (I) state and fails to join the EtherChannel bundle because its Layer 2 switchport setting does not match the Layer 3 configuration of the logical Port-Channel interface.
For a physical interface to join a Layer 3 EtherChannel, both the logical Port-Channel and all member physical interfaces must have 'no switchport' configured. Because GigabitEthernet0/3 retains its default Layer 2 switchport state, it fails the parameter compatibility check and is placed in an independent (I) state in 'show etherchannel summary'.

Step-by-Step Solution

1
Identify the configuration of the logical Port-Channel interface.
Port-channel 10 is configured as a Layer 3 (routed) interface via the 'no switchport' command.
EtherChannel member interfaces must match key operational attributes with the Port-Channel interface, including speed, duplex, trunking/routed mode, and allowed VLANs.
2
Analyze the configuration of physical interface GigabitEthernet0/3.
GigabitEthernet0/3 was added to channel-group 10 without executing 'no switchport'.
By default, switch ports operate as Layer 2 interfaces. Without 'no switchport', GigabitEthernet0/3 remains a Layer 2 port while Port-channel 10 is a Layer 3 port.
3
Determine the outcome in 'show etherchannel summary'.
GigabitEthernet0/3 is marked with the 'I' (Independent) flag and is excluded from the active bundle.
Cisco IOS enforces strict attribute consistency; incompatible physical ports are placed in an independent state and cannot aggregate into the channel.

Key Concept

Layer 3 EtherChannel Member Interface Compatibility Requirements
Question 239Question →

A network administrator is configuring Rapid PVST+ on Switch-A within an enterprise switched topology. Switch-A links to Switch-B and Switch-C over 802.1Q trunk connections carrying multiple VLANs. The administrator executes the command `spanning-tree vlan 20 priority 24576` on Switch-A.

Which two statements correctly describe the resulting Rapid PVST+ operation and configuration characteristics on Switch-A for VLAN 20? (Select two.)

Select all that apply

Show answer & explanation

Answer: Switch-A calculates its effective Bridge Priority for VLAN 20 as 24596 by adding the 12-bit System ID Extension value of 20 to the configured base priority of 24576.; Rapid PVST+ sends BPDUs for VLAN 20 using the IEEE 802.1w structure tagged with a Cisco PVST+ SNAP header destined to multicast MAC address 01-00-0C-CC-CC-CD.

Answer

The correct statements are that Switch-A calculates its effective Bridge Priority for VLAN 20 as 24596 (24576+2024576 + 20) due to the System ID Extension, and that Rapid PVST+ sends BPDUs for VLAN 20 using 802.1w payloads encapsulated in Cisco PVST+ SNAP frames destined to 01-00-0C-CC-CC-CD.
The correct statements recognize that Rapid PVST+ automatically adds the 12-bit VLAN ID (20) to the base priority setting (24576) to form an effective Bridge Priority of 24596, and that Rapid PVST+ encapsulates 802.1w BPDUs into Cisco-specific SNAP frames destined for multicast MAC 01-00-0C-CC-CC-CD.

Step-by-Step Solution

1
Calculate the effective Bridge Priority for VLAN 20
Effective Priority = Base Priority + System ID Extension = 24576+20=2459624576 + 20 = 24596
Cisco Rapid PVST+ implements 802.1t Extended System ID, which combines a 4-bit priority multiplier (in steps of 4096) with the 12-bit VLAN ID to create a unique per-VLAN Bridge ID.
2
Identify the BPDU encapsulation and framing behavior of Rapid PVST+
Rapid PVST+ sends per-VLAN 802.1w RSTP BPDUs tagged over trunks using destination multicast MAC address 01-00-0C-CC-CC-CD
Rapid PVST+ provides rapid convergence per VLAN by running 802.1w mechanics inside Cisco's proprietary PVST+ SNAP frame format.

Key Concept

Rapid PVST+ Bridge ID construction and per-VLAN BPDU frame encapsulation rules
Question 240Question →

A network engineer is configuring interface GigabitEthernet1/0/12 on a Cisco Catalyst switch to connect an end-user workstation. The interface must be explicitly configured as a static, non-trunking Layer 2 port placed into VLAN 75. Which two Cisco IOS CLI commands must be executed within interface configuration mode to achieve this setup? (Select two.)

Select all that apply

Show answer & explanation

Answer: switchport mode access; switchport access vlan 75

Answer

The correct commands to execute in interface configuration mode are 'switchport mode access' and 'switchport access vlan 75'.
Configuring a switch interface for an end-user host requires two distinct steps under interface configuration mode: explicitly declaring the Layer 2 operational mode as access ('switchport mode access') and specifying the target VLAN assignment for untagged frames ('switchport access vlan 75').

Step-by-Step Solution

1
Set the administrative interface mode
Interface is explicitly designated as a Layer 2 access port
Executing 'switchport mode access' under interface configuration mode turns off dynamic trunking negotiations and forces the port into operational access mode.
2
Assign the interface to the target VLAN
Interface forwards untagged traffic into VLAN 75
Executing 'switchport access vlan 75' maps untagged frame ingress and egress on this interface directly to VLAN 75.

Key Concept

Static Access Port Configuration Syntax
Estimated Time:1m 30s
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