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Question 201Question →

A network administrator is establishing a dynamic IEEE 802.3ad Link Aggregation Control Protocol (LACP) Layer 2 EtherChannel bundle between two Cisco Catalyst switches. Physical member interfaces GigabitEthernet1/0/1 and GigabitEthernet1/0/2 are being assigned to channel-group 5. Which two configuration conditions or operational requirements must be satisfied on the local and remote switches for the EtherChannel to successfully negotiate and operationalize both member links? (Select two.)

Select all that apply

Show answer & explanation

Answer: All physical member interfaces within the channel group on a switch must match in speed, duplex mode, and trunking configuration (VLAN membership and native VLAN).; At least one side of the link must be set to LACP active mode, while the opposing side is configured in either active or passive mode.

Answer

The two correct requirements are: 1) Physical member interfaces on a switch must match in speed, duplex, and trunking parameters, and 2) At least one side of the link must be configured in active LACP mode while the opposing side is set to active or passive mode.
The options specifying interface parameter consistency (speed, duplex, trunking settings) and LACP active/passive mode matching are correct. LACP requires physical port settings to be identical across members on the same switch, and at least one connected switch interface must be set to LACP active mode to initiate the 802.3ad negotiation sequence.

Step-by-Step Solution

1
Analyze LACP negotiation protocol requirements
LACP (802.3ad) uses active and passive negotiation modes. Active ports send LACP packets to initiate negotiation, while passive ports only respond to received LACP packets. If both sides are passive, no frames are sent and the EtherChannel fails to negotiate.
Determining dynamic channel formation rules requires evaluating LACP mode compatibility pairings (active-active or active-passive).
2
Verify physical interface parameter consistency
EtherChannel member interfaces must maintain identical speed, duplex, ST P settings, native VLAN, allowed VLANs, and access VLAN assignments. Incompatibilities cause individual ports to be put in an unbundled or suspended state.
Consistency across member interfaces prevents Layer 2 loops and blackholing of switched traffic.
3
Evaluate invalid distractor statements regarding IP configuration and LACP priority
LACP system priority defaults to 32768 and only comes into play during hot-standby port selection when bundling more links than allowed by hardware limits. IP addresses belong on the Port-channel interface for Layer 3 setups, not physical member ports.
Distinguishing essential prerequisites from optional tuning features eliminates false prerequisites.

Key Concept

LACP Interface Consistency and Mode Pairing Requirements
Estimated Time:2m 0s
Question 202Question →

A network engineer is configuring a Layer 3 EtherChannel between two Cisco switches using Link Aggregation Control Protocol (LACP). Which two actions or configurations are required to ensure the EtherChannel forms successfully and routes IP traffic correctly? (Choose two.)

Select all that apply

Show answer & explanation

Answer: Assign the IP address directly to the logical port-channel interface after configuring it as a routed interface using the no switchport command.; Configure the channel-group mode as active on one switch and passive on the opposing switch.

Answer

The correct configurations are assigning the IP address directly to the logical port-channel interface (configured with the no switchport command) and matching an active LACP mode on one switch with a passive LACP mode on the opposing switch.
Layer 3 EtherChannels require IP addresses to be assigned to the logical port-channel interface configured with 'no switchport'. For dynamic LACP bundle creation, at least one switch must be set to active mode while the opposing switch can be passive.

Step-by-Step Solution

1
Identify Layer 3 interface and IP addressing requirements for EtherChannel
Logical Port-Channel interface must have switchport capabilities removed ('no switchport') and receive the IP address assignment.
Layer 3 routing decisions occur at the aggregate logical interface level rather than on individual physical member ports.
2
Evaluate LACP negotiation mode compatibility matrix
Active-passive and active-active pairings form an EtherChannel bundle, whereas passive-passive pairings fail.
At least one side of the link aggregation bundle must actively transmit LACP frames to begin dynamic negotiation.
3
Verify protocol alignment between switches
PAgP modes (desirable/auto) cannot pair with LACP modes (active/passive).
Both endpoints must agree on the underlying aggregation protocol (LACP vs PAgP) for bundle negotiation to succeed.

Key Concept

Layer 3 EtherChannel Configuration and LACP Mode Negotiation
Question 203Question →

An engineer executes the command `show lldp neighbors detail` on a Cisco Catalyst switch to troubleshoot connectivity with an adjacent multi-vendor switch. Below is an excerpt of the command output:

text
Local Intf: Gi0/1
Chassis id: 0025.9611.a480
Port id: Fa0/24
Port Description: Uplink to SW-1
System Name: SW-Edge-02
System Description: Non-Cisco Enterprise Switch OS v12.1
Time remaining: 105 seconds
System Capabilities: Bridge, Router
Enabled Capabilities: Bridge
Management Addresses:
IP: 10.1.100.2
Port VLAN ID: 30

Which statement accurately interprets the neighbor configuration and operational status based on this output?

Show answer & explanation

Answer: The local switch interface GigabitEthernet0/1 is connected to port FastEthernet0/24 on the neighbor device SW-Edge-02, which is operating as a Layer 2 bridge.

Answer

The local switch interface GigabitEthernet0/1 is connected to port FastEthernet0/24 on the neighbor device SW-Edge-02, which is operating as a Layer 2 bridge.
In Cisco IOS `show lldp neighbors detail` output, 'Local Intf' specifies the local interface receiving LLDP messages (GigabitEthernet0/1), while 'Port id' indicates the connected port on the neighbor device (FastEthernet0/24). Additionally, 'Enabled Capabilities' reflects the active operational feature set (Bridge), confirming that the neighbor is currently functioning as a Layer 2 switch on this link.

Step-by-Step Solution

1
Analyze the Local Intf and Port id fields in the LLDP detailed output.
Local Intf is Gi0/1 (the local switch port) and Port id is Fa0/24 (the neighbor device's port).
LLDP explicitly differentiates between the receiving interface on the local switch and the transmitting port advertised by the adjacent neighbor.
2
Evaluate the capabilities fields reported for the neighbor device.
System Capabilities displays Bridge and Router, but Enabled Capabilities lists only Bridge.
Enabled Capabilities represents the active operational role of the neighboring device on the connection, whereas System Capabilities reflects all available hardware capabilities.
3
Examine the Port VLAN ID (PVID) field.
Port VLAN ID 30 is an informational TLV advertised by the neighbor.
Unlike CDP which generates native VLAN mismatch syslog errors when PVIDs mismatch on trunk links, LLDP merely reports the PVID TLV value.

Key Concept

Interpretation of detailed LLDP neighbor outputs, distinguishing local vs remote interfaces and system vs enabled capabilities.
Question 204Question →

A network administrator enables an access switch interface connected to a workstation running standard IEEE 802.1D Spanning Tree Protocol (STP) without PortFast configured. Arrange the standard operational port states in the exact chronological sequence through which the interface transitions from initial link activation to full user data frame transmission.

Drag items to arrange them in the correct order

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Answer

The correct chronological sequence for standard IEEE 802.1D STP port state initialization is: Blocking state, Listening state, Learning state, and finally Forwarding state.
Under standard IEEE 802.1D Spanning Tree Protocol operational behavior, an interface enabling without PortFast goes through a strict multi-step sequence to prevent Layer 2 loops. It begins in the Blocking state (discarding data, listening to BPDUs), transitions to Listening (exchanging BPDUs, electing roles for 15 seconds), advances to Learning (exchanging BPDUs and building MAC address table for 15 seconds), and culminates in the Forwarding state (full data frame transmission and MAC learning).

Step-by-Step Solution

1
Identify the initial state upon link bring-up.
The port initializes in the Blocking state where it drops frames and only listens to BPDUs to avoid loops.
802.1D forces ports to start in Blocking so they can detect BPDUs from neighbor switches before taking any active roles.
2
Determine the second state following election participation.
The port transitions to the Listening state for 15 seconds (Forward Delay).
In Listening state, the switch sends and receives BPDUs to clear invalid topology entries and elect Root/Designated ports without populating MAC tables or forwarding data.
3
Identify the state where MAC address learning begins.
The port transitions to the Learning state for another 15 seconds (Forward Delay).
In Learning state, the port learns source MAC addresses to pre-populate the MAC table, reducing unicast flooding prior to data forwarding.
4
Determine the final operational state.
The port transitions to the Forwarding state.
Having safely passed both Forward Delay periods without loop creation, the port now processes and forwards data traffic normally.

Key Concept

IEEE 802.1D Spanning Tree Protocol Port State Transitions
Estimated Time:2m 0s
Question 205Question →

An administrator observes that workstations connected to switch port GigabitEthernet0/12 experience a 30-second delay before successfully acquiring an IP address from a DHCP server upon initial link up. The switch is running classic 802.1D Spanning Tree Protocol (STP). Which interface configuration command directly resolves this delay, and what is its operational effect on the port?

Show answer & explanation

Answer: Enable `spanning-tree portfast`; it allows the access port to immediately transition from blocking to forwarding state upon link up, bypassing listening and learning states.

Answer

The command `spanning-tree portfast` resolves the issue because it allows an access interface connected to an end-user host to bypass the 15-second Listening and 15-second Learning states, transitioning directly to Forwarding state upon link up.
Enabling `spanning-tree portfast` on an access port connected to a workstation bypasses the standard 802.1D Listening (15 seconds) and Learning (15 seconds) STP states. The interface immediately enters the Forwarding state upon link up, allowing the host to successfully send DHCP requests without timing out.

Step-by-Step Solution

1
Identify the cause of the 30-second delay during host initial boot.
Classic 802.1D STP transitions ports through Blocking → Listening (15s) → Learning (15s) → Forwarding (total 30s delay).
During the Listening and Learning states, data frames (including DHCP Discover messages) are dropped by the switch port.
2
Determine the appropriate Cisco IOS feature for edge ports connected to hosts.
Cisco STP PortFast immediately places edge access ports into the Forwarding state upon link activation.
Host workstations do not create Layer 2 loops, so waiting through convergence states is unnecessary and causes application/DHCP timeouts.

Key Concept

STP PortFast Benefits and Operation
Question 206Question →

A network administrator is examining the operational mechanics of an IEEE 802.1Q trunk link connecting two Cisco switches. Which two statements accurately describe the frame tagging and forwarding behavior of IEEE 802.1Q trunking? (Select two.)

Select all that apply

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Answer: Frames belonging to the native VLAN are forwarded untagged across the trunk link by default.; A 4-byte tag header containing the VLAN ID is inserted into the Ethernet frame header for non-native VLAN traffic.

Answer

IEEE 802.1Q forwards native VLAN frames untagged by default and inserts a 4-byte VLAN tag header into Ethernet frames for all non-native VLAN traffic.
IEEE 802.1Q trunking inserts a 4-byte tag header (including the Tag Protocol Identifier and Tag Control Information) between the Source MAC address and EtherType fields of Ethernet frames for non-native VLAN traffic. For native VLAN traffic, frames are forwarded untagged across the link by default to maintain compatibility.

Step-by-Step Solution

1
Analyze standard 802.1Q frame tagging mechanics.
Identify that 802.1Q inserts a 4-byte header into tagged frames and sends native VLAN frames untagged by default.
802.1Q maintains backwards compatibility with untagged legacy device traffic via the native VLAN concept while identifying other VLANs using the 4-byte tag field.
2
Evaluate the effects of native VLAN mismatches and PortFast configuration on trunk links.
Confirm that native VLAN mismatches lead to cross-VLAN traffic leakage rather than dropping frames, and PortFast on trunk links creates bridging loops.
PortFast bypasses Spanning Tree listening/learning phases, and untagged traffic is processed as belonging to the local native VLAN upon receipt regardless of the sender's VLAN ID.

Key Concept

IEEE 802.1Q Trunking Frame Tagging and Native VLAN Operations
Question 207Question →

A network engineer is configuring a routed (Layer 3) EtherChannel between Switch-1 and Switch-2 using the Link Aggregation Control Protocol (LACP). On Switch-1, the engineer creates `interface Port-channel 5`, configures `no switchport`, and assigns an IP address. On physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2, the engineer enters `no switchport` and `channel-group 5 mode passive`.

Which combination of commands must be configured on Switch-2 for the routed EtherChannel to successfully form and exchange LACP frames?

Show answer & explanation

Answer: Configure 'no switchport' on interface Port-channel 5 and both physical member interfaces, and set 'channel-group 5 mode active' on the physical interfaces.

Answer

Configure 'no switchport' on interface Port-channel 5 and both physical member interfaces, and set 'channel-group 5 mode active' on the physical interfaces.
To establish an LACP EtherChannel bundle when Switch-1 is configured in passive mode, Switch-2 must be set to active mode so it actively sends LACP negotiation frames. Additionally, converting an EtherChannel to Layer 3 requires disabling switchport features using 'no switchport' on both the logical port-channel and the physical member interfaces.

Step-by-Step Solution

1
Analyze the LACP negotiation mode requirement
Switch-1 is set to LACP passive mode, which only responds to LACP requests but does not initiate them.
For LACP to negotiate a bundle, at least one peer must be configured in active mode (Active-Passive or Active-Active).
2
Verify Layer 3 EtherChannel interface requirements
Both the logical Port-channel interface and physical member interfaces must be routed ports ('no switchport').
Layer 3 EtherChannels require consistent routed port configuration across the bundle, with IP addressing applied strictly to the logical Port-channel interface.

Key Concept

Layer 3 EtherChannel LACP Negotiation and CLI Configuration Requirements
Question 208Question →

A switch port (FastEthernet0/12) needs to be assigned to the newly created Sales department VLAN (VLAN 45). Which Cisco IOS command must be executed within interface configuration mode to assign the port to VLAN 45?

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Answer: switchport access vlan 45

Answer

The correct command to assign the interface to VLAN 45 is 'switchport access vlan 45'.
To assign an interface to a specific VLAN in Cisco IOS, the command 'switchport access vlan <vlan-id>' is executed under interface configuration mode.

Step-by-Step Solution

1
Enter interface configuration mode for FastEthernet0/12.
The CLI prompt changes to Switch(config-if)#.
Interface-specific configurations must be applied directly under the target interface context.
2
Execute the command 'switchport access vlan 45'.
Interface FastEthernet0/12 is statically assigned to VLAN 45.
The 'switchport access vlan <vlan-id>' command defines the access VLAN membership for the port.

Key Concept

Static Access Port VLAN Membership Assignment
Estimated Time:45s
Question 209Question →

An engineer executes a verification command on a Cisco Catalyst switch interface connected to a desktop computer:

text
Switch# show spanning-tree interface GigabitEthernet0/1 detail
Port 1 (GigabitEthernet0/1) of VLAN0010 is forwarding
Port path cost 4, Port priority 128.1, Port Identifier 128.1.
Designated root has priority 32778, address 0050.56be.1100
Designated bridge has priority 32778, address 0050.56be.1100
Designated port id is 128.1, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
The port is in the portfast mode
Link type is point-to-point by default
BPDU: sent 1420, received 0

Based on the command output, what will occur in the Spanning Tree Protocol domain when the desktop connected to GigabitEthernet0/1 undergoes a link state flap (disconnects and reconnects)?

Show answer & explanation

Answer: The interface immediately transitions to the Forwarding state upon link-up without generating Topology Change Notifications (TCNs) to upstream switches.

Answer

The interface immediately transitions to the Forwarding state upon link-up without generating Topology Change Notifications (TCNs) to upstream switches.
When Cisco STP PortFast is enabled on an access interface, it provides two main benefits: immediate transition to the Forwarding state (bypassing the 15-second Listening and 15-second Learning states) and suppression of Topology Change Notification (TCN) messages. Because host connections frequently open and close applications or restart, suppressing TCNs prevents the switch from notifying the Root Bridge and forcing all domain switches to temporarily shorten their MAC address table aging timers to Forward Delay (15 seconds).

Step-by-Step Solution

1
Analyze the CLI command output for operational features.
The output explicitly confirms 'The port is in the portfast mode'.
PortFast is enabled on GigabitEthernet0/1, which modifies default 802.1D STP state transition and notification logic.
2
Determine the impact of PortFast on port state transitions during link initiation.
The interface bypasses the 15-second Listening and 15-second Learning timer delays.
PortFast allows an access port connected to a host to move immediately from Blocking to Forwarding.
3
Determine the impact of PortFast on STP domain notifications during link flaps.
No Topology Change Notification (TCN) BPDUs are generated by the switch for this interface event.
Edge port state changes do not represent network topology alterations, so suppressing TCNs prevents unnecessary MAC table timer reductions across the entire switching domain.

Key Concept

Cisco STP PortFast Operational Mechanics and TCN Suppression
Estimated Time:1m 30s
Question 210Question →

A network engineer wants to configure a switch as the primary root bridge for VLAN 20 using Rapid PVST+. What is the lowest valid base bridge priority value that can be specified in the configuration command before the System ID Extension is added?

Show answer & explanation

Answer: 0

Answer

The lowest valid base bridge priority value is 0.
In Rapid PVST+, the base bridge priority is configured in increments of 4096 due to the 12-bit System ID Extension field. The valid range for base priorities is 0 to 61440 in steps of 4096. Therefore, 0 is a valid value and represents the lowest possible base priority.

Step-by-Step Solution

1
Identify the Rapid PVST+ bridge priority configuration rules.
Rapid PVST+ uses the 802.1t System ID Extension, which forces base bridge priority values to be configured in increments of 4096.
The 16-bit Bridge Priority field is divided into a 4-bit Priority field and a 12-bit System ID Extension (VLAN ID).
2
Determine the range of valid base priority values.
Valid base priority values are 0, 4096, 8192, 12288, ..., 61440.
The 4-bit priority multiplier allows values from 0×40960 \times 4096 up to 15×409615 \times 4096.
3
Select the lowest valid configured value.
The minimum allowed base priority is 0 (which results in a total priority of 0+20=200 + 20 = 20 for VLAN 20).
0 is the lowest multiple of 4096.

Key Concept

Rapid PVST+ Bridge Priority and System ID Extension Calculation
Question 211Question →

A network administrator enters the following command sequence on interface GigabitEthernet0/5 of a Cisco Catalyst switch:

text
Switch(config)# interface GigabitEthernet0/5
Switch(config-if)# switchport mode access
Switch(config-if)# switchport access vlan 40

Prior to this configuration, VLAN 40 did not exist in the switch's VLAN database. Which TWO statements correctly describe the behavior and operational result of this configuration? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: VLAN 40 is automatically created in the switch VLAN database if it does not currently exist.; Interface GigabitEthernet0/5 is assigned to VLAN 40 and sends/receives untagged traffic for that VLAN.

Answer

VLAN 40 is automatically generated in the switch database if it was missing, and GigabitEthernet0/5 acts as an access port transmitting untagged frames within VLAN 40.
Executing 'switchport access vlan 40' automatically instantiates VLAN 40 in the switch database if it was not previously configured. Furthermore, setting an interface to access mode ensures it operates within a single VLAN and forwards standard untagged Ethernet frames to connected end-node devices.

Step-by-Step Solution

1
Analyze the command sequence applied to GigabitEthernet0/5.
The interface mode is explicitly set to access ('switchport mode access') and assigned to VLAN 40 ('switchport access vlan 40').
Determines the operating characteristics and membership of the interface.
2
Evaluate Cisco IOS automatic VLAN creation behavior.
Cisco IOS automatically generates VLAN 40 in the VLAN database if it does not already exist when assigned to an access port.
Prevents port assignment failure due to uninitialized VLAN IDs.
3
Evaluate framing behavior for an access port.
Access ports belong to exactly one VLAN and process untagged frames for host endpoints.
Host NICs typically do not recognize or process 802.1Q tagged frames.

Key Concept

VLAN Auto-creation and Access Port Framing Behavior
Estimated Time:1m 30s
Question 212Question →

A network engineer is configuring Layer 2 neighbor discovery on Cisco Catalyst switches and multi-vendor endpoints. Match each Layer 2 discovery protocol characteristic or CLI configuration element on the left with its corresponding operational parameter or behavior on the right.

Click a left item, then click its matching right item

Items

Cisco Discovery Protocol (CDP) Default Timers
Link Layer Discovery Protocol (LLDP) Default Timers
LLDP Interface Directional Control Syntax
LLDP-MED (ANSI/TIA-1057) Capability Target

Matches

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Answer

CDP Default Timers match with a 60-second update transmission interval and 180-second holdtime. LLDP Default Timers match with a 30-second update transmission interval and 120-second holdtime (holdtime multiplier of 4). LLDP Interface Directional Control Syntax matches with granular subcommands allowing outbound frame sending and inbound frame processing to be controlled independently per interface. LLDP-MED Capability Target matches with extending discovery to endpoint devices for voice VLAN assignment, location details, and dynamic Power over Ethernet (PoE) negotiation.
The correct mapping aligns CDP with its proprietary default timers (60s update / 180s holdtime), LLDP with IEEE 802.1AB default timers (30s update / 120s holdtime calculated via a multiplier of 4), interface-level LLDP directional control ('lldp transmit' and 'lldp receive'), and LLDP-MED with multi-vendor endpoint management features (voice VLAN provisioning and dynamic PoE allocation).

Step-by-Step Solution

1
Evaluate the default transmission and holdtime values for CDP and standard LLDP.
CDP defaults to sending announcements every 60 seconds with a 180-second holdtime. IEEE 802.1AB LLDP defaults to sending frames every 30 seconds with a holdtime multiplier of 4 (giving a 120-second holdtime).
Identifying the exact timer specifications avoids confusing vendor-proprietary timer defaults with IEEE standard defaults.
2
Analyze interface configuration mechanisms for directional frame control.
CDP is toggled per interface with 'cdp enable'. LLDP provides independent control over transmission ('lldp transmit') and reception ('lldp receive') at the interface level.
Network security policies often mandate disabling advertisement transmissions on public-facing or untrusted access ports while still permitting inbound neighbor logging.
3
Identify protocol extensions for specialized media endpoints like IP phones.
LLDP-MED (ANSI/TIA-1057) builds upon IEEE 802.1AB by defining specific Type-Length-Value (TLV) headers for Voice VLAN configuration, physical location tracking, and granular power-via-MDI negotiation.
Multi-vendor VoIP deployments rely on LLDP-MED to achieve seamless endpoint provisioning on non-Cisco switches or cross-vendor telephony platforms.

Key Concept

Layer 2 Discovery Protocols (CDP and LLDP Parameters and Configurations)
Question 213Question →

A network administrator needs to create VLAN 100 named VOICE on a Cisco Catalyst switch and assign interface GigabitEthernet0/2 as a static access port in VLAN 100. Starting from Privileged EXEC mode (Switch#Switch\#), in what sequence must the Cisco IOS CLI commands be executed?

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Answer

The correct command sequence begins with entering global configuration mode (configure terminal), creating VLAN 100 (vlan 100), naming the VLAN (name VOICE), navigating to interface GigabitEthernet0/2 (interface gigabitethernet0/2), configuring access mode (switchport mode access), and assigning the port to VLAN 100 (switchport access vlan 100).
The correct order follows Cisco IOS configuration hierarchy. The sequence starts in Privileged EXEC mode with 'configure terminal' to enter Global Configuration mode. Next, 'vlan 100' creates the VLAN and switches to VLAN Configuration mode, where 'name VOICE' is applied. After returning to global configuration scope, 'interface gigabitethernet0/2' opens Interface Configuration mode, where 'switchport mode access' enforces static access behavior and 'switchport access vlan 100' places the port into VLAN 100.

Step-by-Step Solution

1
Transition from Privileged EXEC mode to Global Configuration mode.
The CLI prompt changes to Switch(config)#.
Global configuration mode is required to configure system-wide parameters and enter specific subconfiguration modes.
2
Create VLAN 100 and enter VLAN Configuration submode.
The CLI prompt changes to Switch(config-vlan)#.
VLAN 100 must be instantiated before configuring its parameters or assigning ports.
3
Assign the name VOICE to VLAN 100.
VLAN 100 is assigned the descriptive name VOICE.
The 'name' command is specific to VLAN configuration mode.
4
Navigate to Interface Configuration mode for GigabitEthernet0/2.
The CLI prompt changes to Switch(config-if)#.
Targeting an interface requires switching from global configuration to interface configuration mode.
5
Configure GigabitEthernet0/2 as a static access port.
Trunk negotiation is disabled, establishing static access operation.
Executing 'switchport mode access' explicitly defines the interface operational mode.
6
Assign GigabitEthernet0/2 to VLAN 100.
Untagged frames entering GigabitEthernet0/2 are assigned to broadcast domain VLAN 100.
Executing 'switchport access vlan 100' maps the access port to VLAN 100.

Key Concept

Cisco IOS hierarchical context navigation and sequential syntax execution for VLAN creation and static access port configuration.
Question 214Question →

A network administrator configures Cisco STP PortFast globally on an enterprise access switch. Which two operational benefits or characteristics occur when PortFast is active on an access port connected to a host workstation? (Select two.)

Select all that apply

Show answer & explanation

Answer: The port immediately transitions from the Blocking state to the Forwarding state, skipping the Listening and Learning states.; The switch prevents the generation of Topology Change Notifications (TCNs) when the interface changes link state.

Answer

The correct benefits are that the interface transitions immediately to the Forwarding state (bypassing Listening and Learning states) and that the switch avoids sending Topology Change Notifications (TCNs) when the port status changes.
PortFast is intended for edge ports connected to single end-hosts (such as PCs or printers). It provides two core benefits: immediate transition to the Forwarding state (bypassing the 30-second total Listening and Learning delay) and preventing linkup/linkdown events on host ports from generating Topology Change Notifications (TCNs) that force CAM table aging across the network.

Step-by-Step Solution

1
Analyze standard 802.1D STP convergence timers on edge ports.
Standard STP ports undergo Listening (15 seconds) and Learning (15 seconds) states before reaching Forwarding (total 30 seconds delay), which can cause DHCP client timeouts on host devices.
Identify the primary operational problem PortFast is designed to solve.
2
Evaluate the direct state transition change caused by PortFast.
PortFast allows edge ports to transition immediately from Blocking to Forwarding, bypassing the 30-second convergence delay.
Confirm the first correct operational trait of PortFast.
3
Evaluate the network-wide impact of edge port state changes.
PortFast suppresses TCN generation on edge link flaps, protecting the switch fabric from unnecessary MAC table age-out events.
Confirm the second correct operational benefit of PortFast.

Key Concept

Cisco STP PortFast Operational Behavior and TCN Suppression
Estimated Time:1m 15s
Question 215Question →

An engineer is troubleshooting a routed (Layer 3) EtherChannel between Switch-A and Switch-B. The output of `show etherchannel summary` on Switch-A displays the following status:

text
Group Port-channel Protocol Ports
------+------------+----------+-----------------------------------
10 Po10(SD) LACP Gi0/1(I) Gi0/2(I)

Flags: S - Layer3, D - Down, I - Stand-alone

Switch-A's physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2 are configured with `no switchport` and `channel-group 10 mode active` under interface configuration mode.

Which remote configuration on Switch-B explains why the physical member interfaces on Switch-A remain in a stand-alone (I) state and the port-channel is down (SD)?

Show answer & explanation

Answer: Switch-B has configured member interfaces with `channel-group 10 mode auto`.

Answer

Switch-B has configured member interfaces with `channel-group 10 mode auto`.
The option stating that Switch-B has configured member interfaces with `channel-group 10 mode auto` is correct because `mode auto` enables PAgP negotiation. PAgP and LACP are mutually incompatible protocols; an LACP active interface will never form an EtherChannel with a PAgP auto interface, leaving local ports in the stand-alone (I) state.

Step-by-Step Solution

1
Analyze the `show etherchannel summary` output and flags on Switch-A.
The port-channel Po10 is flagged as `SD` (Layer 3, Down) and member ports Gi0/1 and Gi0/2 are marked with flag `I` (Stand-alone).
Flag `I` indicates the switch is operating physical ports individually because dynamic aggregation negotiation has failed.
2
Examine the local channel-group configuration and protocol on Switch-A.
Switch-A uses LACP (`channel-group 10 mode active`).
An LACP active port sends LACP Data Units (LACPDUs) to solicit aggregation from the remote peer.
3
Evaluate peer negotiation protocol compatibility.
PAgP modes (`auto` and `desirable`) are incompatible with LACP modes (`active` and `passive`).
If Switch-B is configured with `mode auto`, it uses Cisco proprietary PAgP, which does not process or respond to IEEE 802.3ad LACP packets, preventing bundle formation.

Key Concept

LACP vs PAgP Protocol Compatibility and Operational State Verification
Question 216Question →

A network engineer configures Cisco STP PortFast on access layer switch interfaces connected to end-user workstations. Which two statements correctly describe the operational impacts and characteristics of enabling PortFast on these interfaces? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: The interface immediately transitions from the Blocking state to the Forwarding state upon linkup, completely bypassing the Listening and Learning states.; The switch suppresses the generation of Topology Change Notifications (TCNs) when the link state on the PortFast-enabled port transitions up or down.

Answer

PortFast allows an access port to immediately enter the Forwarding state by bypassing the Listening and Learning states, and it suppresses Topology Change Notifications (TCNs) when the port link state changes.
Enabling PortFast on an access interface allows it to bypass the traditional 15-second Listening and 15-second Learning states, transitioning immediately to the Forwarding state. Additionally, PortFast suppresses Topology Change Notifications (TCNs) when the link flaps, preventing unnecessary network-wide MAC address table aging.

Step-by-Step Solution

1
Analyze STP state transitions with PortFast
Standard 802.1D transitions through Blocking (20s max age) -> Listening (15s) -> Learning (15s) -> Forwarding. PortFast immediately places access ports into Forwarding mode upon linkup.
This bypasses the 30-second forward delay, allowing end devices to acquire DHCP IP addresses without timing out.
2
Evaluate Topology Change Notification (TCN) behavior
Link flaps on PortFast-enabled ports do not cause the switch to generate TCN BPDUs toward the Root Bridge.
Prevents unnecessary flooding and shortening of MAC table aging timers across the switch network when user PCs power on or off.
3
Evaluate BPDU handling and security misconceptons
PortFast ports continue to transmit and receive BPDUs unless BPDU Guard or BPDU Filter features are added.
A common misconception is that PortFast disables BPDUs; connecting a switch to a PortFast port without BPDU Guard can lead to transient switching loops.

Key Concept

STP PortFast Operational Characteristics and TCN Suppression
Question 217Question →

A network engineer is configuring an unassigned interface on a Cisco Catalyst switch. The engineer enters interface configuration mode for GigabitEthernet 0/8 and executes the following command sequence:

text
Switch(config)# interface gigabitethernet 0/8
Switch(config-if)# switchport access vlan 42

Prior to entering these commands, VLAN 42 was not present in the switch VLAN database. Assuming default Cisco IOS switchport configuration settings, which outcome occurs as a result of this configuration?

Show answer & explanation

Answer: VLAN 42 is automatically created in the switch VLAN database, and interface GigabitEthernet 0/8 is assigned to forward untagged traffic exclusively within VLAN 42's broadcast domain.

Answer

VLAN 42 is automatically created in the switch VLAN database, and interface GigabitEthernet 0/8 is assigned to forward untagged traffic exclusively within VLAN 42's broadcast domain.
In Cisco IOS, executing 'switchport access vlan <vlan-id>' on an interface when the specified VLAN does not exist causes the switch to automatically create the VLAN in the VLAN database and assign the interface to it. The interface then functions as an access port operating exclusively within the designated broadcast domain.

Step-by-Step Solution

1
Analyze the execution of 'switchport access vlan 42' on a non-existent VLAN ID in Cisco IOS.
Cisco IOS checks the VLAN database. Finding no existing VLAN 42, it generates a console notification ('VLAN 42 does not exist. Creating vlan 42') and automatically adds VLAN 42 with default settings.
Cisco IOS provides dynamic VLAN auto-creation upon assignment to access interfaces to streamline port assignment.
2
Determine the operational state and Layer 2 boundary of GigabitEthernet 0/8.
The port is assigned to access VLAN 42, placing all connected host untagged traffic into VLAN 42's distinct broadcast domain.
Access ports belong to a single access VLAN and process untagged Ethernet frames within that specific broadcast domain.

Key Concept

VLAN Auto-Creation and Access Port Broadcast Domain Isolation
Question 218Question →

A network engineer is operating a four-switch topology (Switch-A, Switch-B, Switch-C, and Switch-D) running Rapid PVST+ for VLAN 50. All inter-switch links are 1 Gbps 802.1Q trunks operating with standard IEEE 802.1D short path costs (cost = 4).

The configured base bridge priorities and MAC addresses for VLAN 50 are as follows:
• Switch-A: Base Priority 24576, MAC 0010.1111.1111
• Switch-B: Base Priority 24576, MAC 0010.2222.2222
• Switch-C: Base Priority 28672, MAC 0010.3333.3333
• Switch-D: Base Priority 32768, MAC 0010.4444.4444

Link connections:
��� Switch-C connects to Switch-A via GigabitEthernet0/1.
• Switch-C connects to Switch-B via GigabitEthernet0/2.
• Switch-D connects directly to Switch-A via GigabitEthernet0/1.
• Switch-D connects directly to Switch-B via GigabitEthernet0/2.
• Switch-A and Switch-B are connected together via two parallel 1 Gbps trunks: Trunk-1 (Gi0/1 on both) and Trunk-2 (Gi0/2 on both). On Switch-A, interface Gi0/1 has port priority 112, and Gi0/2 has port priority 128 (default).

Based on Rapid PVST+ operations for VLAN 50, which port role and state are assigned to interface GigabitEthernet0/2 on Switch-C?

Show answer & explanation

Answer: Alternate port in the Discarding state

Answer

Interface GigabitEthernet0/2 on Switch-C is assigned the Alternate port role and is placed in the Discarding state.
Switch-A is elected Root Bridge for VLAN 50 due to having the lowest Bridge ID (Priority 24576+50=2462624576 + 50 = 24626, MAC 0010.1111.1111). Switch-C's interface Gi0/1 connects directly to Switch-A with a cumulative path cost of 4, making Gi0/1 the Root Port. Interface Gi0/2 on Switch-C connects to Switch-B. Both Switch-B and Switch-C have a Root Path Cost of 4 to reach Switch-A. When electing the Designated Port for the segment connecting Switch-B and Switch-C, Switch-B wins because its Bridge ID (24626.0010.2222.222224626.0010.2222.2222) is lower than Switch-C's Bridge ID (28722.0010.3333.333328722.0010.3333.3333). Therefore, Switch-B's interface becomes Designated Forwarding, and Switch-C's interface Gi0/2 becomes an Alternate port in the Discarding state.

Step-by-Step Solution

1
Calculate the Bridge ID for each switch for VLAN 50 by adding the System ID Extension (VLAN ID 50) to the base bridge priority.
Switch-A Bridge ID: 24576+50=2462624576 + 50 = 24626 with MAC 0010.1111.1111.
Switch-B Bridge ID: 24576+50=2462624576 + 50 = 24626 with MAC 0010.2222.2222.
Switch-C Bridge ID: 28672+50=2872228672 + 50 = 28722 with MAC 0010.3333.3333.
Switch-D Bridge ID: 32768+50=3281832768 + 50 = 32818 with MAC 0010.4444.4444.
Rapid PVST+ uses the 12-bit System ID Extension added to the 4-bit priority field to uniquely identify the bridge priority for each VLAN.
2
Determine the Root Bridge for VLAN 50.
Switch-A is elected Root Bridge because Switch-A and Switch-B tie on priority (24626), but Switch-A has the lower MAC address (0010.1111.1111 < 0010.2222.2222).
The switch with the lowest numerical Bridge ID (Priority + Sys-ID + MAC) becomes the Root Bridge.
3
Determine the Root Port for Switch-C.
Switch-C Gi0/1 connects directly to Root Bridge Switch-A with path cost 4. Switch-C Gi0/2 connects to Switch-B, which has a path cost of 4 to Switch-A (via Gi0/1), making the path via Gi0/2 cost 4+4=84 + 4 = 8. Thus, Switch-C Gi0/1 is the Root Port (Forwarding).
Root Port is selected based on the lowest cumulative Root Path Cost.
4
Determine the role of Switch-C GigabitEthernet0/2 on the link connecting Switch-C and Switch-B.
Both Switch-B and Switch-C advertise a Root Path Cost of 4 on this segment. To elect the Designated Port for the link, compare Bridge IDs of the advertising switches: Switch-B (24626.0010.2222.2222) vs Switch-C (28722.0010.3333.3333). Switch-B has the lower Bridge ID, so Switch-B Gi0/1 becomes the Designated Port (Forwarding). Consequently, Switch-C Gi0/2 becomes an Alternate Port and enters the Discarding state.
In Rapid PVST+, a non-root port receiving superior BPDUs from another switch on a point-to-point link becomes an Alternate port in the Discarding state to maintain a loop-free topology.

Key Concept

Rapid PVST+ Root Bridge Election, Path Cost Calculation, and Alternate Port Role Assignment
Question 219Question →

A network engineer is deploying a Cisco Lightweight Access Point (AP) operating in Local mode. The AP needs to establish a CAPWAP tunnel back to the central Wireless LAN Controller (WLC). Which switch port configuration is required for the access switch interface connected directly to this AP?

Show answer & explanation

Answer: An access port assigned to the untagged VLAN used for AP management traffic.

Answer

An access port assigned to the untagged VLAN used for AP management traffic.
In Local mode, a Cisco Lightweight AP encapsulates all client traffic inside a CAPWAP tunnel sent back to the WLC. Because individual WLAN client VLANs are managed centrally at the controller, the switch port connected to the AP only needs to transmit untagged management traffic. Therefore, configuring the port as an access port in the AP's management VLAN is the correct method.

Step-by-Step Solution

1
Identify the operational mode of the Access Point.
The AP is operating in Local mode.
Local mode APs tunnel all user traffic and management frames directly to the Wireless LAN Controller via CAPWAP.
2
Determine the network access requirement for Local mode AP traffic.
The AP only requires Layer 3 IP reachability to the WLC's management IP address.
Because client VLAN traffic is not locally bridged by the AP, user VLANs do not need to be trunked to the AP.
3
Select the appropriate switch port configuration.
Configure the switch port as a standard Layer 2 access port in the AP management VLAN.
An access port provides the untagged connectivity necessary for the AP to receive an IP address and reach the controller.

Key Concept

Access Point Switchport Configuration in Local Mode
Question 220Question →

An enterprise wireless administrator is integrating a Cisco 5520 Wireless LAN Controller (running AireOS) with a Cisco Catalyst switch stack. The administrator connects four physical distribution system ports on the controller to switch interfaces GigabitEthernet1/0/1 through 1/0/4. The switch interfaces are configured as an 802.1Q trunk bundle using the command `channel-group 1 mode active`. Although Link Aggregation (LAG) has been enabled on the WLC and the controller has been rebooted, the EtherChannel fails to form and all controller distribution links remain down. Which modification on the Catalyst switch stack will resolve this connection failure?

Show answer & explanation

Answer: Change the negotiation protocol on the switch interfaces by executing `channel-group 1 mode on`.

Answer

Change the switch port EtherChannel configuration to static ON mode using `channel-group 1 mode on`.
When Link Aggregation (LAG) is enabled on a Cisco AireOS Wireless LAN Controller, all physical distribution system ports are merged into a single logical interface. AireOS controllers do not support dynamic negotiation protocols such as Link Aggregation Control Protocol (LACP) or Port Aggregation Protocol (PAgP). Therefore, the connected switch ports must be explicitly configured with static link aggregation using the command `channel-group <id> mode on`. Configuring `mode active` forces the switch to expect LACP frames, which the WLC will never transmit, causing the channel to remain down.

Step-by-Step Solution

1
Identify the controller platform and operating system requirements for Link Aggregation (LAG).
Cisco AireOS Wireless LAN Controllers require static EtherChannel bonding across all active distribution system ports.
AireOS software does not support dynamic link aggregation protocols such as LACP (`mode active`/`mode passive`) or PAgP (`mode desirable`/`mode auto`).
2
Analyze the current switch configuration.
The switch interfaces are set to `channel-group 1 mode active`, which requires LACP negotiation packets from the connected device.
Because the AireOS WLC never sends LACP frames, the switch ports remain suspended in an unbundled state awaiting negotiation.
3
Determine the necessary configuration change on the switch ports.
Change `channel-group 1 mode active` to `channel-group 1 mode on` on all connecting interfaces.
Configuring `mode on` disables negotiation protocol requirements and forces the switch interfaces into a functional EtherChannel bundle matching the WLC behavior.

Key Concept

WLAN Controller Link Aggregation (LAG) EtherChannel Switch Configuration
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