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Network Access

400 questions

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Question 181Question →

A network administrator checks the operational state of link GigabitEthernet0/1 connecting two switches, SW-Core and SW-Access. Both switch interfaces are operating with default factory switchport settings, which sets their Dynamic Trunking Protocol (DTP) mode to dynamic auto. Which two outcomes describe the state of this connection? (Select two.)

Select all that apply

Show answer & explanation

Answer: The interface operationally functions as a Layer 2 access port in VLAN 1.; To establish an active trunk connection using dynamic negotiation, at least one interface must be configured as dynamic desirable.

Answer

The interface operationally functions as a Layer 2 access port in VLAN 1, and establishing a trunk via dynamic negotiation requires at least one interface to be set to dynamic desirable.
When both ends of a switch-to-switch link operate in default dynamic auto mode, neither switch interface sends DTP negotiation packets to initiate a trunk. Consequently, the operational status of both ports remains in access mode operating in the default VLAN 1. For dynamic trunking negotiation to succeed, at least one of the connected interfaces must actively request a trunk by being configured in dynamic desirable mode.

Step-by-Step Solution

1
Analyze the default Cisco Dynamic Trunking Protocol (DTP) mode settings.
Both interfaces on SW-Core and SW-Access are in dynamic auto mode.
Dynamic auto mode listens for DTP frame requests but never actively initiates trunk negotiation.
2
Evaluate the DTP negotiation state table for auto-to-auto connections.
The link fails to form a trunk and defaults to access operational state.
Since neither side sends DTP trunking requests, the negotiation stays passive and defaults to access mode.
3
Determine the necessary configuration changes to form a dynamic trunk.
At least one side must be switched to dynamic desirable (or statically set to trunk).
Dynamic desirable actively sends DTP packets to request trunk negotiation from the opposing dynamic auto switch port.

Key Concept

DTP mode negotiation combinations and operational defaults for 802.1Q trunks
Question 182Question →

Network administrators must understand the key attributes, IEEE standards, and default operational parameters of Layer 2 discovery protocols when configuring enterprise switches. Match each Layer 2 discovery protocol characteristic on the left with its corresponding protocol specification or value on the right.

Click a left item, then click its matching right item

Items

IEEE 802.1AB
CDP Default Advertisement Interval
LLDP Default Holdtime
Cisco Discovery Protocol (CDP)

Matches

Show answer & explanation

Answer

IEEE 802.1AB matches the open IEEE standard defining LLDP; CDP Default Advertisement Interval matches 60 seconds; LLDP Default Holdtime matches 120 seconds; Cisco Discovery Protocol (CDP) matches the Cisco-proprietary Layer 2 discovery protocol enabled by default on Cisco Catalyst switches.
Each item accurately corresponds to its defining standard, default timer, or vendor status. IEEE 802.1AB specifies LLDP; CDP advertises every 60 seconds; LLDP retains neighbor entries for a default holdtime of 120 seconds (30s x 4); and CDP is a Cisco-proprietary protocol enabled out of the box.

Step-by-Step Solution

1
Identify the standard specification for LLDP
IEEE 802.1AB defines vendor-neutral LLDP
Standardization allows multi-vendor interoperability for discovery protocols.
2
Determine default CDP update interval
CDP transmits periodic updates every 60 seconds by default
Cisco IOS uses 60 seconds for update packets and 180 seconds for holdtime.
3
Calculate default LLDP holdtime value
LLDP transmit timer (30s) multiplied by holdtime multiplier (4) equals 120 seconds
LLDP calculates holdtime dynamically based on transmit frequency and multiplier.
4
Identify proprietary characteristics of CDP
CDP is Cisco-proprietary and active by default on Cisco hardware
Unlike LLDP, CDP does not require global enablement on standard Cisco switch platforms.

Key Concept

Layer 2 Discovery Protocols (CDP and LLDP) Timers and Standards
Estimated Time:1m 0s
Question 183Question →

A network administrator needs to establish a routed (Layer 3) EtherChannel between two Cisco switches using LACP active mode across physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2. In what correct chronological order should the administrator execute the Cisco IOS CLI commands to configure this Layer 3 EtherChannel from global configuration mode?

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Answer

The correct configuration order requires selecting physical member interfaces first, converting them to Layer 3 routed ports using 'no switchport', assigning them to EtherChannel group 10 with LACP active mode, entering Port-channel 10 configuration mode, and finally configuring the IPv4 address on the logical Port-channel interface.
The correct order follows Cisco standard CLI logic for Layer 3 EtherChannel configuration: select physical member interfaces ('interface range GigabitEthernet0/1 - 2'), convert them to routed ports ('no switchport'), form the LACP EtherChannel bundle ('channel-group 10 mode active'), navigate into the logical interface ('interface Port-channel 10'), and assign the IP address ('ip address 10.10.10.1 255.255.255.252').

Step-by-Step Solution

1
Select physical member interfaces
Entered interface range configuration mode for GigabitEthernet0/1 - 2.
CLI commands must be applied to physical interfaces first before grouping them into a bundle.
2
Execute 'no switchport' on physical member interfaces
Member interfaces are converted from Layer 2 switch ports to Layer 3 routed ports.
A Layer 3 EtherChannel requires member interfaces to be configured as routed interfaces before establishing the channel group.
3
Execute 'channel-group 10 mode active'
Physical interfaces are added to Port-channel 10 under LACP active negotiation mode.
The channel-group command dynamically creates the Port-channel interface with LACP protocol.
4
Enter logical interface mode via 'interface Port-channel 10'
Router moves into logical interface configuration prompt.
Layer 3 configurations (IP addressing) must be defined on the logical port-channel interface itself.
5
Apply IP address parameters on Port-channel 10
IP address 10.10.10.1/30 is bound to Port-channel 10.
Traffic routing across Layer 3 EtherChannel uses the logical interface IP address.

Key Concept

Layer 3 EtherChannel CLI configuration workflow requires setting 'no switchport' on physical member interfaces prior to creating the channel-group and applying IP addressing on the logical Port-channel interface.
Question 184Question →

A network administrator is troubleshooting an inter-switch link failure between Switch-1 and Switch-2. Switch-1 is configured for a Layer 3 EtherChannel, but the bundle fails to form, and Switch-2 is unable to route traffic across the link.

On Switch-1, the relevant configuration is:
text
interface Port-channel 5
ip address 10.10.50.1 255.255.255.252
!
interface range GigabitEthernet0/1 - 2
no switchport
channel-group 5 mode active

On Switch-2, the administrator issues the `show etherchannel 5 summary` command, which displays the following output:
text Flags: D - down P - bundled in port-channel I - stand-alone s - suspended H - Hot-standby s - Layer2 U - in use R - Layer3 S - Layer2 F - failed to allocate aggregator Group Port-channel Protocol Ports ------+------------+----------+----------------------------------------------- 5 Po5(SD) LACP Gi0/1(I) Gi0/2(I)

Additionally, inspecting `show running-config interface GigabitEthernet0/1` on Switch-2 reveals:
text
interface GigabitEthernet0/1
channel-group 5 mode passive

Which condition is the primary root cause of Switch-2 placing GigabitEthernet0/1 and GigabitEthernet0/2 into stand-alone `(I)` state and Port-channel 5 into Switch-port Down `(SD)` state?

Show answer & explanation

Answer: Switch-2 member interfaces are operating as default Layer 2 ports because `no switchport` was omitted on the physical member interfaces prior to or after adding them to the port-channel.

Answer

Switch-2 member interfaces are operating as default Layer 2 ports because `no switchport` was omitted on the physical member interfaces prior to or after adding them to the port-channel.
For a Layer 3 EtherChannel to aggregate properly, both switches must configure physical member ports and logical port-channel interfaces with the `no switchport` command. Switch-1 configured member interfaces as routed ports, while Switch-2 retained default Layer 2 behavior (indicated by the `S` flag in `Po5(SD)`). Because Layer 2 ports cannot bundle with Layer 3 ports across LACP peers, Switch-2 falls back to placing its physical interfaces into stand-alone `(I)` mode.

Step-by-Step Solution

1
Analyze the Switch-1 configuration
Switch-1 explicitly executes `no switchport` on physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2 and sets `channel-group 5 mode active` to create a routed (Layer 3) LACP EtherChannel.
Layer 3 EtherChannels require physical interfaces to operate in unswitched (routed) mode.
2
Inspect the CLI output flags on Switch-2
Flag `S` indicates Layer 2 operational mode and flag `D` indicates Down for `Po5(SD)`. Flag `I` indicates Stand-alone state for `Gi0/1(I)` and `Gi0/2(I)`.
When physical interfaces remain in default Layer 2 mode (`switchport`) while the peer switch expects Layer 3 routed interfaces, parameter mismatches prevent LACP bundle aggregation, forcing member ports into stand-alone state.
3
Evaluate LACP operational compatibility
LACP negotiation requires consistent Layer 2/Layer 3 port characteristics between peer switches.
To resolve the issue, Switch-2 must execute `no switchport` on both physical interfaces and `interface Port-channel 5`.

Key Concept

Layer 3 EtherChannel Member Interface Requirements
Question 185Question →

A network administrator needs to create VLAN 20 on a Cisco Catalyst switch and configure interface GigabitEthernet0/1 as an access port belonging to VLAN 20. Arrange the CLI commands in the correct sequence, starting from privileged EXEC mode.

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Answer

The correct CLI configuration sequence begins by entering global configuration mode with 'configure terminal', creating the VLAN with 'vlan 20', navigating to the target interface with 'interface GigabitEthernet0/1', defining static access mode via 'switchport mode access', and finally binding the interface to the VLAN using 'switchport access vlan 20'.
The configuration progression follows Cisco IOS hierarchical logic: enter global configuration mode ('configure terminal'), create the VLAN in the database ('vlan 20'), transition to the specific interface context ('interface GigabitEthernet0/1'), force the link to operate as an access link ('switchport mode access'), and assign it to the desired broadcast domain ('switchport access vlan 20').

Step-by-Step Solution

1
Enter global configuration mode
Switch prompt changes to Switch(config)#
Global configuration mode is required before creating VLANs or specifying interface configurations.
2
Create VLAN 20
VLAN 20 is added to the database and prompt changes to Switch(config-vlan)#
Creating the VLAN ensures the broadcast domain exists prior to assigning switch ports to it.
3
Enter interface configuration mode for GigabitEthernet0/1
Switch prompt changes to Switch(config-if)#
Interface parameters must be configured within the specific interface configuration context.
4
Configure static access mode on the interface
Disables DTP trunk negotiation and sets interface to access mode
Explicitly declaring access mode ensures the port will not form a trunk link.
5
Assign the interface to VLAN 20
Interface GigabitEthernet0/1 is placed into VLAN 20
Associates untagged layer 2 traffic on GigabitEthernet0/1 with broadcast domain VLAN 20.

Key Concept

Cisco IOS CLI hierarchy for VLAN creation and switchport access assignment
Question 186Question →

A network administrator is verifying a newly deployed link aggregation bundle between Switch-A and Switch-B. The command `show etherchannel summary` on Switch-A displays Port-channel 5 as `Po5(SD)` with member interfaces `GigabitEthernet1/0/1(I)` and `GigabitEthernet1/0/2(I)` running protocol `LACP`. On Switch-B, `show etherchannel summary` displays `Po5(SD)` with member interfaces `GigabitEthernet1/0/1(I)` and `GigabitEthernet1/0/2(I)` running protocol `PAgP`.

Which TWO statements accurately describe why Port-channel 5 fails to bundle and remains in a down state?

Select all that apply

Show answer & explanation

Answer: Switch-A and Switch-B are running conflicting EtherChannel negotiation protocols, which prevents dynamic link aggregation setup.; Switch-B physical interfaces were configured with `channel-group 5 mode auto` or `channel-group 5 mode desirable`, which explicitly selects PAgP instead of LACP.

Answer

The bundle fails because Switch-A and Switch-B are configured with mismatched EtherChannel protocols (LACP vs. PAgP), caused by Switch-B using `channel-group 5 mode auto` or `mode desirable`.
EtherChannel requires both endpoints to run the same aggregation protocol. Switch-A is configured for LACP (via `mode active` or `mode passive`), whereas Switch-B is configured for PAgP (via `mode auto` or `mode desirable`). Because LACP and PAgP control frames are incompatible, negotiation fails, leaving member interfaces in standalone state `(I)` and the port-channel down `(SD)`.

Step-by-Step Solution

1
Analyze the `show etherchannel summary` protocol column for Switch-A and Switch-B.
Switch-A displays protocol `LACP`, while Switch-B displays protocol `PAgP`.
LACP and PAgP use completely different control frame formats and state machines, making them mutually incompatible.
2
Evaluate the interface CLI configuration that causes Switch-B to run PAgP.
Switch-B member interfaces were assigned using PAgP mode commands (`channel-group 5 mode auto` or `channel-group 5 mode desirable`).
To operate with LACP, Switch-B member interfaces must be configured using `channel-group 5 mode active` or `channel-group 5 mode passive`.
3
Verify flags `(SD)` and `(I)` in the command output.
`S` indicates Layer 2, `D` indicates Down, and `I` indicates Standalone mode.
Because protocol negotiation fails, member interfaces drop to standalone `(I)` mode and the port-channel interface stays down `(SD)`.

Key Concept

Layer 2 EtherChannel LACP vs. PAgP Protocol Compatibility and CLI Mode Selection
Question 187Question →

A network engineer is setting up a dynamic Layer 2 EtherChannel between Switch-A and Switch-B using the Link Aggregation Control Protocol (LACP). Switch-A is configured on its member interfaces with `channel-group 10 mode active`. The engineer wants Switch-B to form the EtherChannel by only responding to incoming LACP negotiation requests without actively sending initial negotiation frames. Which command should be applied to Switch-B's member interfaces?

Show answer & explanation

Answer: channel-group 10 mode passive

Answer

The correct command is `channel-group 10 mode passive` because LACP passive mode responds to incoming LACP negotiation packets sent by an LACP active peer without actively initiating LACP frame transmissions.
The command `channel-group 10 mode passive` configures the interface to use LACP in a passive role. When connected to a device in LACP active mode (such as Switch-A), the passive interface receives the active LACP frames, responds to them, and successfully forms an EtherChannel bundle.

Step-by-Step Solution

1
Identify the protocol in use on Switch-A.
Switch-A uses `channel-group 10 mode active`, which identifies IEEE 802.3ad LACP in active negotiation mode.
EtherChannel negotiation protocols must match on both ends (LACP to LACP).
2
Determine the required operating mode for Switch-B.
Switch-B must operate in LACP passive mode.
LACP passive mode waits to receive LACP packets and responds to them, allowing the bundle to form when paired with an active peer.
3
Evaluate protocol options to select the correct CLI command.
`channel-group 10 mode passive` matches the exact requirement for LACP passive behavior.
Modes such as `auto` and `desirable` use PAgP instead of LACP, and `on` disables dynamic protocol negotiation completely.

Key Concept

LACP EtherChannel Mode Compatibility and Operation
Question 188Question →

A network administrator is configuring a secure interswitch 802.1Q trunk link on Cisco switch interface GigabitEthernet0/1. The task requires statically enabling trunking, stopping DTP frame negotiation, reassigning the native VLAN to VLAN 99, and removing VLAN 1 from the trunk's allowed list. Place the CLI commands and actions in the correct logical configuration order.

Drag items to arrange them in the correct order

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Answer

The correct sequence begins by entering interface mode, enforcing static trunking, disabling DTP negotiation, setting native VLAN 99, and finally removing VLAN 1 from the allowed VLAN list.
Configuring a static 802.1Q trunk on a Cisco Catalyst switch requires stepping into interface configuration mode first. Setting switchport mode trunk must precede switchport nonegotiate because DTP disabling is rejected by Cisco IOS on dynamic interfaces. Configuring native VLAN 99 and pruning VLAN 1 completes the trunk hardening workflow.

Step-by-Step Solution

1
Execute interface GigabitEthernet0/1 in global configuration mode.
Enters interface configuration context.
Port configuration parameters must be applied within the specific interface context.
2
Execute switchport mode trunk.
Sets administrative state to unconditional trunking.
Cisco IOS requires an explicit static mode (trunk or access) prior to issuing switchport nonegotiate.
3
Execute switchport nonegotiate.
Stops transmission of DTP frames.
Prevents unauthorized trunk negotiation while ensuring the link remains statically operational.
4
Execute switchport trunk native vlan 99.
Configures VLAN 99 as the native untagged VLAN.
Overrides default VLAN 1 untagged frame behavior to prevent security issues such as VLAN hopping.
5
Execute switchport trunk allowed vlan remove 1.
Removes VLAN 1 from the trunk forwarding topology.
Ensures default management VLAN traffic does not traverse the interswitch link.

Key Concept

802.1Q Trunk CLI Configuration Order and DTP Prerequisites
Question 189Question →

An administrator on Switch-A attempts to add VLAN 40 to an operational IEEE 802.1Q trunk interface currently forwarding traffic for VLANs 10, 20, and 30. The administrator executes the command `switchport trunk allowed vlan 40` in interface configuration mode. Immediately after, users in VLANs 10, 20, and 30 lose connectivity across the trunk link. Which command should the administrator have executed to add VLAN 40 without disrupting existing VLAN traffic?

Show answer & explanation

Answer: switchport trunk allowed vlan add 40

Answer

The administrator should use the command 'switchport trunk allowed vlan add 40'.
In Cisco IOS, executing `switchport trunk allowed vlan <ids>` overwrites the existing list of allowed VLANs on a trunk interface. To preserve existing allowed VLANs while adding a new VLAN, the `add` keyword must be explicitly included.

Step-by-Step Solution

1
Analyze the impact of the executed command 'switchport trunk allowed vlan 40'.
Executing 'switchport trunk allowed vlan 40' replaces the entire trunk allowed list with only VLAN 40, removing VLANs 10, 20, and 30 from being allowed across the link.
Omitting parameter modifiers causes Cisco IOS to completely overwrite the current allowed VLAN list with the specified list.
2
Determine the correct Cisco IOS command syntax to append a VLAN to an active trunk allowed list.
The correct command syntax is 'switchport trunk allowed vlan add 40'.
The 'add' keyword instructs the switch to append VLAN 40 to the existing list rather than replacing it.

Key Concept

802.1Q Trunk Allowed VLAN Modification
Estimated Time:1m 0s
Question 190Question →

A network administrator is deploying non-Cisco VoIP IP phones connected to a Cisco Catalyst switch. While Cisco Discovery Protocol (CDP) is enabled by default, the non-Cisco devices require Link Layer Discovery Protocol (LLDP) to receive VLAN assignments and power settings. Which command must the administrator execute in global configuration mode to enable LLDP globally across the switch?

Show answer & explanation

Answer: lldp run

Answer

The command `lldp run` entered in global configuration mode enables LLDP globally across the Cisco switch.
The command `lldp run` is executed in global configuration mode to start the LLDP service switch-wide on Cisco devices. Once enabled globally, individual interfaces will transmit and receive LLDP advertisements.

Step-by-Step Solution

1
Identify the protocol requirement
LLDP (IEEE 802.1AB) is required for interoperability with non-Cisco devices.
CDP is Cisco-proprietary, whereas LLDP is an open standard supported across multi-vendor equipment.
2
Determine the global CLI configuration syntax for LLDP
The command to enable LLDP globally on Cisco IOS is `lldp run`.
In Cisco IOS/IOS-XE, global protocol enablement for LLDP follows the syntax `lldp run` (similar to `ip routing` or `cdp run`).

Key Concept

Global activation of LLDP on Cisco Catalyst switches
Estimated Time:45s
Question 191Question →

An engineer executes the `show spanning-tree interface gigabitethernet 1/0/10` command on a Cisco switch after connecting a desktop PC. The output displays the port in the STP Learning state. What is the operational behavior of interface GigabitEthernet 1/0/10 while in this port state?

Show answer & explanation

Answer: The interface populates the MAC address table from incoming frames but does not forward user data traffic.

Answer

The interface populates the MAC address table from incoming frames but does not forward user data traffic.
In classic IEEE 802.1D Spanning Tree Protocol, the Learning state allows the switch port to learn source MAC addresses from frames received on the port and populate the switch MAC address table. However, to prevent Layer 2 loops while topology information stabilizes, the port does not yet forward user data frames or relay frames between interfaces.

Step-by-Step Solution

1
Analyze standard 802.1D Spanning Tree Protocol port states in chronological sequence.
The progression order is Blocking → Listening → Learning → Forwarding.
Understanding the function of each state ensures correct identification of port behavior.
2
Examine the specific actions permitted during the Learning state.
The port receives and sends BPDUs, and reads incoming frames to populate the MAC address table, but user traffic forwarding remains disabled.
Learning MAC addresses before entering the Forwarding state reduces initial unicast flooding once forwarding begins.

Key Concept

802.1D STP Port State Operational Characteristics
Estimated Time:1m 15s
Question 192Question →

A network administrator needs to configure a routed (Layer 3) EtherChannel using LACP dynamic negotiation across physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2 on a Cisco switch. Place the configuration steps in the correct sequential order from first to last.

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Answer

The correct sequence of steps to configure a Layer 3 EtherChannel using LACP is: 1) Enter interface range configuration mode for the physical member interfaces; 2) Execute the 'no switchport' command on the physical member interfaces; 3) Execute the 'channel-group 1 mode active' command on the physical member interfaces; 4) Enter logical interface Port-channel 1 configuration mode and assign the IPv4 address and subnet mask.
The proper administrative workflow begins by selecting physical member links GigabitEthernet0/1 and GigabitEthernet0/2. Disabling Layer 2 switching on these interfaces via 'no switchport' establishes them as routed interfaces. Binding them to channel-group 1 using LACP active mode creates the logical port-channel and begins dynamic trunk negotiation. Finally, navigating into interface Port-channel 1 mode permits configuration of the routed IP address.

Step-by-Step Solution

1
Select physical member links
Switch prompt changes to (config-if-range).
Allows configuration changes to be applied simultaneously across both physical interfaces.
2
Disable Layer 2 switchport mode on physical interfaces
'no switchport' command converts physical member links into routed ports.
Layer 3 EtherChannels require member interfaces to operate as routed ports rather than Layer 2 switchports.
3
Enable LACP active mode on physical interfaces
'channel-group 1 mode active' dynamically creates logical interface Port-channel 1.
Active mode ensures the switch actively initiates LACP negotiation across the member links.
4
Assign IP address to the logical port-channel
IPv4 address and subnet mask are configured on interface Port-channel 1.
For Layer 3 EtherChannels, IP routing occurs on the aggregate logical interface.

Key Concept

Layer 3 EtherChannel LACP Configuration Sequence
Estimated Time:1m 0s
Question 193Question →

An administrator is troubleshooting an interswitch link between SwitchA and SwitchB. Interface GigabitEthernet0/2 on SwitchA is configured with 'switchport mode dynamic desirable'. Interface GigabitEthernet0/2 on SwitchB is configured with 'switchport mode dynamic auto'. Trunking is successfully established, but the console displays periodic '%CDP-4-NATIVE_VLAN_MISMATCH' warning messages. What is the root cause of this error message?

Show answer & explanation

Answer: The two connected switch interfaces are configured with different native VLAN IDs.

Answer

The two connected switch interfaces are configured with different native VLAN IDs.
Cisco Discovery Protocol (CDP) periodically sends Layer 2 messages containing native VLAN information across switch links. When an 802.1Q trunk link is established between two switches, both sides must agree on the native VLAN ID. If one switch port is configured with native VLAN 1 and the other with native VLAN 99, CDP detects the mismatch and emits the %CDP-4-NATIVE_VLAN_MISMATCH console alert.

Step-by-Step Solution

1
Analyze DTP negotiation status between dynamic desirable and dynamic auto.
Dynamic desirable actively initiates DTP negotiation while dynamic auto responds, resulting in a successfully established 802.1Q trunk link.
Understanding DTP mode matrix confirms trunk operational status.
2
Analyze the syslog error message %CDP-4-NATIVE_VLAN_MISMATCH.
Cisco Discovery Protocol (CDP) exchanges Native VLAN Type-Length-Value (TLV) fields between neighboring switches across the trunk link.
When the native VLAN configured on one end of an 802.1Q trunk does not match the native VLAN on the opposing end, CDP triggers this specific warning log.

Key Concept

802.1Q Native VLAN Inconsistency and CDP Detection
Estimated Time:1m 15s
Question 194Question →

To reduce network join latency for desktop computers during operating system startup, a Cisco switch interface connected to an end-user host is configured with PortFast. Which specific operational behavior does PortFast introduce on this interface?

Show answer & explanation

Answer: The interface bypasses the Listening and Learning states to transition directly from Blocking to Forwarding upon link initialization.

Answer

The interface bypasses the Listening and Learning states to transition directly from Blocking to Forwarding upon link initialization.
Enabling PortFast on an access port allows the switch interface to transition immediately into the Forwarding state upon detecting link status up, bypassing the normal Listening (15 seconds) and Learning (15 seconds) STP states. This eliminates initialization delays for end hosts such as workstations and servers.

Step-by-Step Solution

1
Identify standard 802.1D STP port state transition timers for access ports.
Standard 802.1D STP transitions through Blocking -> Listening (15s) -> Learning (15s) -> Forwarding, totaling 30 seconds of convergence delay.
During Listening and Learning states, user data frames are dropped while the switch listens for BPDUs and populates its MAC address table.
2
Analyze the functional impact of enabling Cisco STP PortFast on an access interface.
PortFast causes the interface to skip the 15-second Listening and 15-second Learning delay, moving immediately into the Forwarding state when the physical link comes up.
End-user workstations do not create Layer 2 loops, so delaying data forwarding for 30 seconds is unnecessary and causes application initialization timeouts.

Key Concept

STP PortFast operational mechanics and state bypass
Question 195Question →

Which Cisco Wireless LAN Controller (WLC) interface is dedicated exclusively to out-of-band management and operates on an isolated physical port separate from wireless client data traffic?

Show answer & explanation

Answer: Service port

Answer

The Service port is dedicated exclusively to out-of-band management.
The Service port is a dedicated physical port on a Cisco WLC used strictly for out-of-band management. It remains completely isolated from the controller's distribution system ports, CAPWAP tunnel termination, and wireless client data traffic.

Step-by-Step Solution

1
Identify the requirement for out-of-band management isolation on a Cisco Wireless LAN Controller.
Out-of-band management requires a dedicated physical interface isolated from client data traffic and CAPWAP tunnels.
This separation allows administrators to reach the controller even if in-band network interfaces or distribution trunks experience failures.
2
Evaluate the functionality of the WLC Service port.
The Service port is a dedicated physical port used exclusively for out-of-band system administration via protocols such as HTTPS and SSH.
Unlike in-band interfaces, the Service port does not carry CAPWAP tunnel traffic or wireless user data traffic.

Key Concept

Cisco WLC Service Port for Out-of-Band Management Access
Question 196Question →

During a network audit, a network engineer discovers that `spanning-tree portfast default` is enabled globally on an access switch. A junior technician subsequently connects an unmanaged switch to one of the access ports. Assuming BPDU Guard is NOT configured on the port, what occurs when the Cisco switch interface receives a Spanning Tree Protocol (STP) BPDU from the unmanaged switch?

Show answer & explanation

Answer: The interface immediately loses its PortFast operational status, transitions to the Blocking state, and moves through standard IEEE 802.1D port states.

Answer

The interface immediately loses its PortFast operational status, transitions to the Blocking state, and moves through standard IEEE 802.1D port states.
Cisco PortFast allows end-user host ports to bypass the 30-second STP listening and learning delays and enter the forwarding state immediately. However, PortFast does not disable BPDU processing. If a PortFast-enabled interface receives an STP BPDU (indicating a switch or hub is attached), the interface loses its PortFast status and reverts to standard 802.1D STP operation, transitioning to the Blocking state to safely evaluate network topology and prevent bridging loops.

Step-by-Step Solution

1
Analyze PortFast behavior upon receiving BPDUs without BPDU Guard
PortFast allows an access port to immediately move from Blocking to Forwarding, skipping Listening and Learning states. However, it does not stop the port from sending or receiving BPDUs.
PortFast is designed strictly for edge ports connected to single end-user devices.
2
Evaluate the interface state transition when a BPDU arrives
When a BPDU is received on a PortFast-enabled interface without BPDU Guard active, the switch detects another bridge device. PortFast operational status is immediately revoked, and the port falls back to standard IEEE 802.1D state transitions.
Falling back to normal STP port states (Blocking -> Listening -> Learning -> Forwarding) protects the network from potential Layer 2 loops.

Key Concept

PortFast BPDU Handling and Operational State Reversion
Question 197Question →

A network engineer is auditing Layer 2 discovery protocol operation on a Cisco Catalyst switch connected to multi-vendor wireless access points and VoIP endpoints. The engineer executes the CLI command `show lldp entry AP-Floor2` on switch SW-1 and views the following output:

text
Capability codes:
(R) Router, (B) Bridge, (T) Telephone, (W) WLAN Access Point, (P) Repeater, (O) Other

Local Interface: Gi1/0/12
Chassis id: 0027.0d4f.8e10
Port id: Gi0/1
Port Description: GigabitEthernet0/1
System Name: AP-Floor2
System Description: Autonomous AP Software v15.3
Time remaining: 98 seconds
System Capabilities: B, W
Enabled Capabilities: W
Management Address: 10.1.20.15
Management Address Port VLAN ID (PVID): 20

Which statements accurately interpret the operational state and protocol fields in this command output? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: The neighbor device is connected to local switch interface GigabitEthernet1/0/12, while GigabitEthernet0/1 identifies the port on the remote neighbor device.; The neighbor device advertises System Capabilities as both a Bridge and a WLAN Access Point, but currently functions with only its WLAN Access Point capability enabled.

Answer

The correct statements are that GigabitEthernet1/0/12 is the local switch interface while GigabitEthernet0/1 is the remote port ID, and that the neighbor supports Bridge and WLAN Access Point capabilities but operates with only WLAN Access Point enabled.
The output from `show lldp entry` provides Layer 2 neighbor discovery details defined by IEEE 802.1AB. The 'Local Interface' line specifies that switch port GigabitEthernet1/0/12 receives the frames, whereas 'Port id' indicates GigabitEthernet0/1 on the remote device. Additionally, the System Capabilities field shows all capabilities supported by the device hardware (Bridge and WLAN Access Point), while Enabled Capabilities indicates that only WLAN Access Point functionality is actively enabled.

Step-by-Step Solution

1
Analyze interface mapping in LLDP CLI output.
Identify 'Local Interface: Gi1/0/12' as the switch's local receiving port and 'Port id: Gi0/1' as the remote neighbor's transmitting interface.
Layer 2 discovery outputs distinguish between local interfaces and remote neighbor port identifiers to accurately identify physical topology connections.
2
Evaluate system and enabled capabilities codes.
System Capabilities lists 'B, W' (Bridge and WLAN Access Point), while Enabled Capabilities lists 'W'.
LLDP TLVs allow neighbor devices to report both their full hardware features and currently active functional roles.
3
Distinguish LLDP protocol parameters from CDP parameters.
Confirm LLDP operates under IEEE 802.1AB standard with a 120-second default holdtime (30s timer × 4 hold multiplier), contrasting CDP's 180-second default holdtime (60s timer × 3).
Recognizing protocol defaults prevents confusing open-standard LLDP data with Cisco proprietary CDP frames.

Key Concept

Interpretation of IEEE 802.1AB LLDP entry output and TLV field mappings
Estimated Time:2m 0s
Question 198Question →

A network administrator is manually configuring a Cisco switch to become the root bridge for VLAN 10 using Rapid PVST+. Which value is valid to specify with the command `spanning-tree vlan 10 priority <value>`?

Show answer & explanation

Answer: 24576

Answer

The valid bridge priority setting is 24576, as Rapid PVST+ requires configurable priority values to be in increments of 4096.
In Rapid PVST+, the configurable bridge priority must be a multiple of 4096 (0,4096,8192,…,614400, 4096, 8192, \dots, 61440). The value 24576 is 6×40966 \times 4096, making it a valid configuration parameter. The switch automatically adds the VLAN ID (10) to the base priority to create the combined Bridge Identifier priority of 24586.

Step-by-Step Solution

1
Identify the Rapid PVST+ bridge priority structure requirement
Rapid PVST+ uses the 802.1t System ID Extension, dividing the 16-bit Bridge Priority field into a 4-bit priority component and a 12-bit VLAN ID component.
Because 4 bits are reserved for priority, values can only change by steps of 212=40962^{12} = 4096.
2
Evaluate the candidate values for multiples of 4096
24576/4096=624576 / 4096 = 6, which is an exact integer multiple.
The CLI requires entering the base priority multiplier (6×4096=245766 \times 4096 = 24576), and the switch will internally add VLAN 10 to yield a total priority of 24586.

Key Concept

Rapid PVST+ Bridge Priority Increment Calculation
Estimated Time:45s
Question 199Question →

A network engineer configures interface GigabitEthernet0/1 on Switch-1 with the commands `switchport mode trunk` and `switchport nonegotiate`. The connected interface GigabitEthernet0/1 on Switch-2 remains in its default configuration of `switchport mode dynamic auto`. What is the resulting operational state of interface GigabitEthernet0/1 on Switch-2?

Show answer & explanation

Answer: It operates as an access port because it does not receive Dynamic Trunking Protocol (DTP) frames from Switch-1 to trigger trunk negotiation.

Answer

Interface GigabitEthernet0/1 on Switch-2 operates as an access port because `switchport nonegotiate` on Switch-1 suppresses DTP frames, leaving Switch-2 in its default passive access state.
The command `switchport nonegotiate` turns off DTP frame generation on Switch-1. Because interface GigabitEthernet0/1 on Switch-2 is set to `dynamic auto`, it relies on receiving incoming DTP negotiation frames to transition to a trunking state. Receiving no DTP frames from Switch-1, Switch-2 stays in its default operational mode of access, resulting in a misconfiguration where Switch-1 trunks while Switch-2 acts as an access port.

Step-by-Step Solution

1
Analyze the DTP configuration on Switch-1
Switch-1 is configured statically as a trunk (`switchport mode trunk`) and DTP frame transmission is disabled using `switchport nonegotiate`.
The `nonegotiate` command stops the interface from sending DTP frames to neighboring devices.
2
Analyze the DTP operational behavior on Switch-2
Switch-2 is in `switchport mode dynamic auto`, which means it will form a trunk only if it receives a DTP request frame (desirable or trunk mode) from the remote switch.
Dynamic auto interfaces never actively originate DTP negotiation requests; they remain passive.
3
Determine the resulting link operational state
Because Switch-1 sends no DTP frames, Switch-2 never receives the signal to become a trunk and defaults to an operational access port.
A link connecting a static trunk with `nonegotiate` to a `dynamic auto` interface creates a mode mismatch where one side is trunking and the other is an access port.

Key Concept

802.1Q Trunking DTP Negotiation and Nonegotiate Interaction
Question 200Question →

A network engineer configures an interface on a Cisco Catalyst switch operating in VTP Client mode by executing the command switchport access vlan 50 under interface configuration mode. Upon verifying the port status using the show interfaces gigabitethernet 1/0/1 switchport command, the output indicates Access Mode VLAN: 50 (Inactive). What is the root cause of this inactive status, and how should it be resolved?

Show answer & explanation

Answer: VLAN 50 does not exist in the VLAN database propagated by the VTP Server; VLAN 50 must be created on the VTP Server switch.

Answer

VLAN 50 does not exist in the VLAN database propagated by the VTP Server; VLAN 50 must be created on the VTP Server switch.
When a port is assigned to an access VLAN on a Cisco Catalyst switch, the VLAN must exist in the VLAN database for the port to forward traffic. On switches in VTP Server or VTP Transparent mode, executing 'switchport access vlan X' automatically creates VLAN X in the database if it does not already exist. However, switches operating in VTP Client mode cannot modify the local VLAN database directly or auto-create VLANs. If the assigned VLAN does not exist in the VTP database advertised by the VTP Server, the switchport output displays the access mode VLAN as '(Inactive)'. To resolve this issue, VLAN 50 must be created on the VTP Server so that it is propagated to the VTP Client switch.

Step-by-Step Solution

1
Analyze the switch operating mode and CLI output
The switch operates in VTP Client mode, and interface Gi1/0/1 displays 'Access Mode VLAN: 50 (Inactive)'.
VTP Client switches learn VLAN definitions dynamically from VTP Server advertisements and do not allow local creation or auto-creation of VLAN entries.
2
Determine the cause of the '(Inactive)' VLAN status
On Cisco switches, an access VLAN is marked 'Inactive' when a port is assigned to a VLAN ID that is not present in the local VLAN database.
While switches in VTP Server or Transparent mode automatically create a missing VLAN upon interface assignment, VTP Client switches cannot auto-create VLAN entries.
3
Identify the required corrective action
Configure VLAN 50 on the VTP Server switch.
Once VLAN 50 is created on the VTP Server, it will be advertised via VTP updates to the client switch, populating the local VLAN database and activating the port.

Key Concept

VLAN Database Inactive Status and VTP Client Behavior
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