Examkin

Network Access

400 questions

All types400Multiple choice204Multiple select91Matching23Ordering82
Question 141Question →

A network engineer connects two Cisco Catalyst switches. SwitchA interface GigabitEthernet0/1 is configured with 'switchport mode dynamic desirable', and SwitchB interface GigabitEthernet0/1 is configured with 'switchport mode dynamic auto'. Both switches use default native VLAN 1 configurations. Place the following operational events in the correct sequential order from the initiation of link negotiation to the transmission of native VLAN traffic.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence begins with SwitchA sending active DTP frames, followed by SwitchB acknowledging the proposal from dynamic auto mode, both interfaces transitioning to operational 802.1Q trunking, SwitchA receiving ingress VLAN 1 traffic, and SwitchA forwarding that native VLAN traffic untagged across the trunk.
Dynamic desirable ports actively initiate DTP negotiation, causing dynamic auto ports to respond and agree. Once operational, data traffic matching the default native VLAN (VLAN 1) is forwarded across the 802.1Q trunk untagged.

Step-by-Step Solution

1
Initiate DTP Proposal
SwitchA sends DTP frames via Gi0/1.
'switchport mode dynamic desirable' actively initiates negotiation with the neighbor.
2
Respond to Negotiation
SwitchB receives DTP and responds positively.
'switchport mode dynamic auto' will not originate DTP proposals but willingly converts to a trunk if requested by a neighbor.
3
Establish Operational Trunk
Both Gi0/1 interfaces enter the trunking operational state using 802.1Q encapsulation.
A desirable-to-auto dynamic DTP pairing successfully negotiates a trunk.
4
Process Ingress Frame
SwitchA accepts an ingress frame belonging to VLAN 1 (native VLAN).
Data plane forwarding occurs after control plane negotiation is established.
5
Forward Across Trunk
SwitchA sends the frame across Gi0/1 untagged.
By default under 802.1Q, native VLAN traffic is transmitted without adding a 4-byte VLAN tag.

Key Concept

802.1Q Trunking DTP Negotiation Sequence and Native VLAN Tagging Mechanics
Question 142Question →

An engineer executes the command `show interfaces gigabitethernet 0/1 switchport` on a Cisco Catalyst switch and receives the following output:

text
Name: Gi0/1
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 10 (VLAN0010)
Administrative Native VLAN tagging: enabled
Trunking VLANs Enabled: 10, 20, 30

How will the switch handle an outgoing frame belonging to VLAN 10 as it egresses interface GigabitEthernet0/1?

Show answer & explanation

Answer: The frame will be transmitted with an explicit 802.1Q VLAN tag containing VLAN ID 10 because global native VLAN tagging is enabled.

Answer

The switch will transmit the frame with an explicit 802.1Q tag for VLAN 10 because global native VLAN tagging is active on the switch.
Standard IEEE 802.1Q trunking sends frames belonging to the native VLAN without a VLAN tag. However, when native VLAN tagging is enabled globally (`vlan dot1q tag native`), the switch appends an 802.1Q tag header (VLAN ID 10) to all outgoing native VLAN frames across 802.1Q trunks.

Step-by-Step Solution

1
Analyze the operational parameters in the CLI output.
The interface is operating as an 802.1Q trunk ('Operational Mode: trunk', 'Operational Trunking Encapsulation: dot1q') with VLAN 10 configured as the native VLAN ('Trunking Native Mode VLAN: 10').
Understanding the interface trunk encapsulation and native VLAN assignment sets the baseline for frame processing.
2
Evaluate the native VLAN tagging state.
The output states 'Administrative Native VLAN tagging: enabled', indicating that the global command 'vlan dot1q tag native' is in effect.
By default, 802.1Q native VLAN frames are transmitted untagged, but enabling global native VLAN tagging forces all native VLAN egress frames to be explicitly tagged.

Key Concept

802.1Q Native VLAN Tagging Behavior
Question 143Question →

An engineer is troubleshooting a Layer 2 connectivity issue between Switch-1 and Switch-2 connected via GigabitEthernet0/1. A host in VLAN 10 connected to Switch-1 is unable to reach a host in VLAN 10 on Switch-2. A partial CLI output from Switch-1 is shown below:

text
Switch-1# show interfaces gigabitethernet 0/1 switchport
Name: Gi0/1
Administrative Mode: dynamic auto
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 10
Administrative Native VLAN tagging: disabled
Trunking VLANs Enabled: 10,20,30

Switch-2's GigabitEthernet0/1 interface is configured as an 802.1Q trunk with `switchport trunk native vlan 20` and allows VLANs 10, 20, and 30. CDP logs on both switches generate regular native VLAN mismatch warnings.

Assuming global native VLAN tagging (`vlan dot1q tag native`) is disabled on both switches, how will Switch-2 process an untagged ARP request broadcast generated by the host in VLAN 10 on Switch-1 when it arrives at Switch-2's GigabitEthernet0/1 interface?

Show answer & explanation

Answer: Switch-2 will accept the untagged frame and forward it internally into VLAN 20, preventing VLAN 10 hosts on Switch-2 from receiving the ARP request.

Answer

Switch-2 will accept the untagged frame and forward it internally into VLAN 20, preventing VLAN 10 hosts on Switch-2 from receiving the ARP request.
Under standard 802.1Q operation without global native VLAN tagging, frames originating on the native VLAN of an egress trunk interface are sent untagged. Switch-1's native VLAN is 10, so VLAN 10 traffic is transmitted without an 802.1Q header. When Switch-2 receives an untagged frame on a trunk port, it automatically maps that frame to its own configured native VLAN, which is VLAN 20. As a result, the ARP broadcast leaks into VLAN 20 on Switch-2, failing to reach hosts on VLAN 10.

Step-by-Step Solution

1
Analyze Switch-1 trunk egress behavior for VLAN 10 traffic.
Switch-1 has native VLAN configured as VLAN 10 without global native VLAN tagging enabled. Therefore, frames belonging to VLAN 10 are transmitted across the 802.1Q trunk link without an 802.1Q VLAN tag.
By default in 802.1Q trunking, traffic belonging to the configured native VLAN is sent untagged.
2
Analyze Switch-2 trunk ingress behavior for untagged frames.
Switch-2 receives an untagged frame on GigabitEthernet0/1. According to 802.1Q standard operations, any untagged frame received on a trunk interface is automatically mapped to that interface's configured native VLAN.
Switch-2's configured native VLAN is VLAN 20.
3
Determine internal forwarding destination and traffic impact.
The untagged ARP request from VLAN 10 on Switch-1 is forwarded internally into VLAN 20 on Switch-2. Hosts on VLAN 10 attached to Switch-2 never receive the broadcast ARP frame.
Native VLAN mismatch causes cross-VLAN traffic leaking into the receiving switch's native VLAN rather than maintaining isolation or reaching the intended source VLAN.

Key Concept

802.1Q Native VLAN Untagged Ingress Forwarding and Mismatch Mechanics
Estimated Time:2m 0s
Question 144Question →

Which TWO statements accurately describe standard IEEE 802.1Q trunking behavior on Ethernet switch interfaces? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: By default, traffic belonging to the native VLAN is transmitted across the trunk link without an added 802.1Q VLAN tag.; An 802.1Q tag header inserts a 4-byte field containing a VLAN Identifier (VID) into the Ethernet frame header for non-native VLAN traffic.

Answer

The correct statements are that native VLAN frames are transmitted untagged by default across an 802.1Q trunk link, and that 802.1Q encapsulation inserts a 4-byte header containing the VLAN ID into non-native VLAN frames.
Under IEEE 802.1Q trunking, traffic belonging to the native VLAN is sent untagged by default without an added header. For all other VLANs traversing the trunk, the switch inserts a 4-byte tag header into the original Ethernet frame containing the VLAN ID.

Step-by-Step Solution

1
Analyze frame tagging behavior for 802.1Q trunking
Recognize that 802.1Q inserts a 4-byte VLAN tag into Ethernet frames for tagged VLANs, but leaves native VLAN frames untagged by default.
This dual behavior allows legacy untagged devices and native traffic to traverse trunk links.
2
Evaluate native VLAN configuration requirements across trunk links
Confirm that native VLAN IDs must match on both ends of the interswitch trunk.
Mismatched native VLAN IDs cause frames originating in one VLAN to exit into a different VLAN on the receiving switch.
3
Evaluate Spanning Tree Protocol (STP) PortFast application
Confirm that PortFast is intended strictly for edge access ports connected to end-user devices.
Enabling PortFast on switch-to-switch interconnect trunks can lead to catastrophic bridging loops during topology changes.

Key Concept

IEEE 802.1Q Trunk Header Mechanics and Native VLAN Operation
Estimated Time:1m 0s
Question 145Question →

An administrator connects two Cisco switches, Switch-1 and Switch-2, using interface GigabitEthernet0/1. Switch-1 is configured with `switchport mode dynamic desirable`, `switchport trunk native vlan 20`, and `switchport trunk allowed vlan 10,20,30`. Switch-2 is configured with `switchport mode dynamic auto`, `switchport trunk native vlan 20`, and `switchport trunk allowed vlan 10,30`. Which statement correctly describes the operational status and traffic behavior across this interswitch link?

Show answer & explanation

Answer: An 802.1Q trunk link forms successfully via DTP negotiation, but Switch-2 drops all ingress traffic for VLAN 20 because VLAN 20 is not included in its allowed VLAN list.

Answer

An 802.1Q trunk link forms successfully via DTP negotiation, but Switch-2 drops all ingress traffic for VLAN 20 because VLAN 20 is not included in its allowed VLAN list.
DTP successfully negotiates trunking between dynamic desirable and dynamic auto operational modes. However, trunk interface allowed VLAN lists filter traffic independently on each switch. Because Switch-2 has configured `switchport trunk allowed vlan 10,30`, VLAN 20 is explicitly pruned from Switch-2's trunk interface. Untagged traffic for native VLAN 20 arriving on Switch-2 will be mapped to VLAN 20 and subsequently dropped because VLAN 20 is not permitted on the trunk.

Step-by-Step Solution

1
Analyze the Dynamic Trunking Protocol (DTP) mode negotiation between Switch-1 and Switch-2.
Switch-1 (dynamic desirable) actively sends DTP frames, while Switch-2 (dynamic auto) responds. A operational 802.1Q trunk link is established.
Matching allowed VLAN lists are not required for DTP to successfully negotiate a trunk link.
2
Evaluate the native VLAN frame tagging mechanics for Switch-1.
Switch-1 transmits frames for VLAN 20 without an 802.1Q tag across the trunk.
By default in 802.1Q trunking, traffic belonging to the native VLAN is sent untagged.
3
Evaluate Switch-2 ingress processing and allowed VLAN pruning logic.
Switch-2 receives untagged frames, associates them with native VLAN 20, but drops them because VLAN 20 is not present in `switchport trunk allowed vlan 10,30`.
The `switchport trunk allowed vlan` command acts as an ingress and egress filter on trunk interfaces.

Key Concept

802.1Q Trunking DTP Negotiation and Allowed VLAN Pruning Mechanics
Estimated Time:1m 30s
Question 146Question →

Two Cisco Catalyst switches, Switch-A and Switch-B, are connected via their GigabitEthernet0/1 interfaces. Switch-A has its interface configured with the command `switchport mode dynamic desirable`, while Switch-B operates using the default Cisco Catalyst DTP configuration (`switchport mode dynamic auto`). Both switches retain all default VLAN parameters. Which of the following statements regarding the operational behavior of this interswitch connection are true? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: The interface link successfully negotiates an operational 802.1Q trunking state via Dynamic Trunking Protocol (DTP).; Traffic belonging to VLAN 1 is transmitted across the trunk link without an added 802.1Q VLAN header tag.

Answer

The connection successfully negotiates an operational 802.1Q trunk link via DTP, and frames belonging to the default native VLAN (VLAN 1) are transmitted across the trunk untagged.
When combining `switchport mode dynamic desirable` on one end and `switchport mode dynamic auto` on the other, DTP successfully negotiates an operational trunk. Furthermore, because default settings maintain VLAN 1 as the native VLAN, frames associated with VLAN 1 are forwarded across the trunk without receiving a 4-byte 802.1Q VLAN header tag.

Step-by-Step Solution

1
Analyze the Dynamic Trunking Protocol (DTP) mode combination between Switch-A and Switch-B.
Switch-A (`dynamic desirable`) actively sends DTP negotiation frames. Switch-B (`dynamic auto`) listens and agrees to form a trunk upon receiving DTP requests from a desirable port.
DTP operational state rules dictate that desirable + auto results in an operational trunk.
2
Evaluate the 802.1Q native VLAN framing mechanics for default VLAN configuration.
VLAN 1 is the default native VLAN on both switches. Under IEEE 802.1Q standards, frames belonging to the designated native VLAN cross the trunk link untagged.
802.1Q tagging adds a 4-byte header only to non-native VLAN traffic to ensure backward compatibility and minimal processing overhead for native subnet traffic.

Key Concept

802.1Q Trunking and Dynamic Trunking Protocol (DTP) Negotiation
Estimated Time:1m 30s
Question 147Question →

A network engineer connects two Cisco Catalyst switches using interface GigabitEthernet0/12. The interfaces are configured with the following parameters:

Switch_Alpha (GigabitEthernet0/12):
- DTP Mode: `dynamic desirable`
- Trunking Encapsulation: `dot1q`
- Native VLAN: `20`
- Allowed VLANs: `10, 20, 30`

Switch_Beta (GigabitEthernet0/12):
- DTP Mode: `dynamic auto`
- Trunking Encapsulation: `dot1q`
- Native VLAN: `1`
- Allowed VLANs: `10, 30, 40`

Which two operational outcomes will occur on this interconnect link? (Select two.)

Select all that apply

Show answer & explanation

Answer: The link will successfully negotiate an operational 802.1Q trunk state.; Cisco Discovery Protocol (CDP) will generate error messages warning of a native VLAN mismatch.

Answer

The link will successfully negotiate an operational 802.1Q trunk state, and Cisco Discovery Protocol (CDP) will generate error messages warning of a native VLAN mismatch.
DTP mode 'dynamic desirable' actively negotiates trunking with 'dynamic auto', resulting in an operational trunk link. Additionally, because the two switches have conflicting native VLAN configurations (VLAN 20 vs VLAN 1), CDP exchange mechanisms detect the PVID mismatch and generate warning log alerts.

Step-by-Step Solution

1
Analyze DTP negotiation state between the two switches
Dynamic desirable initiates trunk negotiation while dynamic auto responds to requests. The combination successfully forms an operational 802.1Q trunk link.
DTP requires at least one side to be in desirable or trunk mode to actively negotiate a trunk.
2
Evaluate the native VLAN configuration on both interface endpoints
Switch_Alpha treats VLAN 20 as native, while Switch_Beta treats VLAN 1 as native.
Mismatched native VLAN definitions do not prevent DTP state completion, but cause CDP to detect PVID mismatches and log critical warning messages.
3
Verify allowed VLAN filtering rules and frame tagging behavior
Allowed VLAN lists do not restrict DTP state negotiation, and native VLAN frames remain untagged by default on 802.1Q trunks unless global native VLAN tagging is enabled.
802.1Q trunking sends frames belonging to the configured local native VLAN across the link without adding a 4-byte 802.1Q VLAN header.

Key Concept

802.1Q Trunking DTP Negotiation and Native VLAN Mismatch Behaviors
Question 148Question →

An enterprise network switch, Switch-A, is connected to Switch-B via interface GigabitEthernet0/1. Switch-A is configured with `switchport mode dynamic desirable` and `switchport trunk native vlan 50`. Switch-B is configured with `switchport mode dynamic auto` and `switchport trunk native vlan 1`. Spanning Tree Protocol (STP) and Cisco Discovery Protocol (CDP) are enabled on both switches. Which TWO operational outcomes occur on this interswitch link? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: The interface operational mode successfully negotiates to an IEEE 802.1Q trunk link.; CDP generates periodic console messages warning of a native VLAN mismatch between the switches.

Answer

The interswitch link successfully negotiates an operational IEEE 802.1Q trunk via DTP, and CDP periodically logs native VLAN mismatch notifications.
An IEEE 802.1Q trunk forms successfully because a port configured as dynamic desirable actively negotiates with a port in dynamic auto mode. Additionally, because Switch-A defines VLAN 50 as native while Switch-B defines VLAN 1 as native, CDP detects the inconsistency through TLV messages and generates native VLAN mismatch warnings.

Step-by-Step Solution

1
Analyze the Dynamic Trunking Protocol (DTP) operational modes configured on both ends of the link.
Switch-A (`dynamic desirable`) actively sends DTP frames, and Switch-B (`dynamic auto`) listens and responds.
The combination of dynamic desirable and dynamic auto results in successful trunk negotiation.
2
Analyze IEEE 802.1Q native VLAN egress tagging and ingress processing behavior.
Switch-A sends VLAN 50 frames untagged, while Switch-B expects native VLAN traffic on VLAN 1 untagged.
By default, 802.1Q trunks transmit frames belonging to the configured native VLAN without an 802.1Q header.
3
Evaluate Layer 2 discovery protocol diagnostics for native VLAN consistency.
CDP exchanges native VLAN information via TLVs, detects the mismatch (VLAN 50 vs VLAN 1), and logs `%CDP-4-NATIVE_VLAN_MISMATCH` console messages.
CDP continuously monitors interswitch link parameters to highlight Layer 2 misconfigurations.

Key Concept

DTP operational mode negotiation and IEEE 802.1Q native VLAN mismatch behavior
Question 149Question →

A switch interface configured as an IEEE 802.1Q trunk receives an Ethernet frame that does not contain a 4-byte 802.1Q VLAN tag. How does the switch process this incoming frame?

Show answer & explanation

Answer: It assigns the frame to the native VLAN configured on the trunk port.

Answer

The switch assigns the untagged frame to the native VLAN configured on the trunk port.
Under IEEE 802.1Q trunking standards, traffic belonging to the configured native VLAN is transmitted across the trunk link without inserting a 4-byte VLAN tag. When an untagged frame arrives at an 802.1Q trunk interface, the receiving switch assigns that frame to its configured native VLAN.

Step-by-Step Solution

1
Examine frame encapsulation on the 802.1Q trunk link.
Identify that the incoming frame lacks a 4-byte 802.1Q VLAN tag header.
802.1Q trunking transmits and receives native VLAN traffic without appending a VLAN tag.
2
Apply 802.1Q native VLAN processing rules.
Map the untagged frame to the native VLAN assigned to the trunk interface.
Standard 802.1Q mechanics dictate that untagged frames arriving on a trunk interface belong to the configured native VLAN.

Key Concept

802.1Q Native VLAN untagged frame handling
Question 150Question →

Two Cisco Catalyst switches, Switch-1 and Switch-2, are connected directly via their GigabitEthernet0/1 interfaces. Switch-1 is configured with `switchport trunk native vlan 99` and `switchport trunk allowed vlan 10,20,99`. Switch-2 is configured with `switchport trunk native vlan 10` and `switchport trunk allowed vlan 10,20,99`. A workstation connected to an access port in VLAN 99 on Switch-1 transmits an untagged broadcast frame. Assuming both trunk ports are operational, how will Switch-2 process this frame upon receiving it over the trunk link?

Show answer & explanation

Answer: Switch-2 accepts the untagged frame, assigns it to its own configured native VLAN (VLAN 10), and forwards it to ports within VLAN 10.

Answer

Switch-2 accepts the untagged frame, assigns it to its own configured native VLAN (VLAN 10), and forwards it to ports within VLAN 10.
Under IEEE 802.1Q trunking rules, frames belonging to the trunk's native VLAN are transmitted untagged. Switch-1 transmits the VLAN 99 broadcast frame without an 802.1Q tag because VLAN 99 is its local native VLAN. When Switch-2 receives this untagged frame on its trunk interface, it associates the frame with its own configured native VLAN (VLAN 10). As a result, the frame is processed within VLAN 10 on Switch-2, causing cross-VLAN traffic leakage.

Step-by-Step Solution

1
Analyze frame egress from Switch-1
Switch-1 receives the broadcast in VLAN 99. Because VLAN 99 is configured as the native VLAN on Switch-1's trunk interface, Switch-1 strips/omits the 802.1Q header tag and sends the frame untagged across the trunk link.
By definition in IEEE 802.1Q, traffic belonging to the native VLAN is transmitted across a trunk without an inserted 4-byte 802.1Q VLAN tag.
2
Analyze frame ingress at Switch-2
Switch-2 receives an untagged Ethernet frame on its trunk interface GigabitEthernet0/1.
The frame arrives without any 802.1Q tag identifying its originating VLAN.
3
Apply native VLAN ingress mapping logic on Switch-2
Switch-2 maps the incoming untagged frame to its local native VLAN, which is VLAN 10.
A switch trunk interface always associates untagged incoming frames with its own locally configured native VLAN setting.
4
Determine forwarding domain
The broadcast frame is flooded to all operational access ports in VLAN 10 on Switch-2.
Traffic sent on VLAN 99 on Switch-1 leaks directly into VLAN 10 on Switch-2 due to the native VLAN mismatch.

Key Concept

IEEE 802.1Q Native VLAN Ingress/Egress Processing and Mismatch Behavior
Question 151Question →

Place the operational and negotiation events in the exact chronological sequence required for two Cisco Catalyst switches to establish a functional IEEE 802.1Q trunk link using Dynamic Trunking Protocol (DTP) following CLI configuration.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence begins with the CLI mode configuration on both switches, followed by Switch-A actively sending DTP request frames, Switch-B processing and agreeing to the trunking request, the operational transition of both interfaces to an active 802.1Q trunk, and finally the active forwarding and 4-byte tagging of frame traffic.
The correct order follows the standard Cisco IOS control and data plane progression: Configuration commands activate DTP on the interface -> The dynamic desirable interface actively sends DTP negotiation frames -> The dynamic auto interface receives the frame and agrees to form a trunk -> Both ports transition operationally to trunking status -> IEEE 802.1Q 4-byte frame tagging is applied to active traffic.

Step-by-Step Solution

1
Identify administrative configuration stage
Switch-A is set to dynamic desirable and Switch-B is set to dynamic auto.
Administrative commands must be applied to the interfaces before any control-plane negotiation protocols can generate messages.
2
Determine active protocol packet generation
Switch-A sends DTP frames actively across the link.
Dynamic desirable ports actively initiate negotiation by sending DTP frames, whereas dynamic auto ports only listen until prompted.
3
Analyze protocol response and parameter matching
Switch-B receives the DTP request and responds affirmatively.
Dynamic auto mode transitions to a trunk state upon receiving an active negotiation request from a desirable or trunking neighbor.
4
Establish operational port state
Both ports transition to operational status trunking with 802.1Q encapsulation.
Once parameters are agreed upon, hardware state registers update the port state from access to trunking.
5
Apply data-plane framing rules
Ethernet frames traversing the link receive a 4-byte 802.1Q VLAN header, except for frames belonging to the native VLAN.
Data forwarding and 802.1Q frame encapsulation occur only after trunk negotiation and port state activation are fully finalized.

Key Concept

802.1Q Trunking & DTP Negotiation Sequence
Question 152Question →

An administrator issues the `show interfaces trunk` command on Switch-A while troubleshooting inter-switch connectivity to Switch-B. The command output confirms that interface GigabitEthernet1/0/1 is actively trunking using 802.1Q encapsulation. However, syslog messages periodically display `%CDP-4-NATIVE_VLAN_MISMATCH` notifications because Switch-A is configured with native VLAN 30 while Switch-B uses native VLAN 1. Which two statements accurately describe how frames are handled across this link? (Select two.)

Select all that apply

Show answer & explanation

Answer: Frames generated by hosts in VLAN 30 on Switch-A are transmitted across the trunk link without an 802.1Q header tag.; Untagged frames arriving at Switch-B from Switch-A will be placed into VLAN 1, resulting in cross-VLAN traffic leakage.

Answer

Frames originating from VLAN 30 on Switch-A are transmitted without an 802.1Q tag, and Switch-B associates incoming untagged frames with its own native VLAN (VLAN 1).
Under IEEE 802.1Q specifications, traffic matching the native VLAN of the transmitting switch interface is sent without an 802.1Q header. Because Switch-A has a native VLAN of 30, it sends VLAN 30 frames untagged. Upon receiving untagged frames, Switch-B associates them with its own native VLAN (VLAN 1). This results in unexpected cross-VLAN communication between VLAN 30 on Switch-A and VLAN 1 on Switch-B.

Step-by-Step Solution

1
Identify the egress frame tagging behavior on Switch-A.
Because VLAN 30 is designated as the native VLAN on Switch-A, frames belonging to VLAN 30 are forwarded across the trunk without an 802.1Q tag.
Under 802.1Q trunking rules, frames matching the local native VLAN of the transmitting port are sent untagged.
2
Identify the ingress frame processing behavior on Switch-B.
Switch-B receives the untagged frame and assigns it to its configured native VLAN, which is VLAN 1.
Receiving switches process all incoming untagged Ethernet frames within whatever VLAN is locally configured as native on that receiving trunk port.

Key Concept

802.1Q Native VLAN Tagging Mechanics and Mismatch Behavior
Question 153Question →

A network administrator needs to create a new VLAN named 'VOICE' with ID 20 on a fresh Cisco Catalyst switch and manually assign interface FastEthernet 0/1 as an active access port belonging to this VLAN. Place the Cisco IOS CLI commands in the exact correct sequence required to perform this complete configuration from privileged EXEC mode.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct operational order begins by entering global configuration mode (configure terminal), creating the VLAN (vlan 20), naming the VLAN (name VOICE), entering interface mode (interface fastethernet 0/1), explicitly setting the link to access mode (switchport mode access), and finally binding the port to the VLAN (switchport access vlan 20).
Cisco IOS configuration follows a strict modal hierarchy. The administrator must first enter global configuration mode (`configure terminal`), instantiate VLAN 20 (`vlan 20`), name it while in `config-vlan` sub-mode (`name VOICE`), navigate to the desired interface (`interface fastethernet 0/1`), set the operational mode (`switchport mode access`), and assign the access VLAN (`switchport access vlan 20`).

Step-by-Step Solution

1
Enter Global Configuration mode
Switch prompt changes to Switch(config)#
CLI context must be in global configuration mode to create network-wide objects such as VLANs or navigate to specific interfaces.
2
Create VLAN 20
Switch prompt changes to Switch(config-vlan)#
Executing 'vlan 20' creates the L2 broadcast domain in the VLAN database and shifts context to VLAN configuration mode.
3
Assign the VLAN Name
VLAN 20 is named 'VOICE'
Sub-commands like 'name' must be issued while in Config-VLAN mode directly following VLAN creation.
4
Navigate to target switchport interface
Switch prompt changes to Switch(config-if)#
Interface commands require entering interface configuration mode for FastEthernet 0/1.
5
Set port operational mode to access
DTP dynamic negotiation is disabled or overridden to static access mode
Best security and operational practice requires explicitly defining 'switchport mode access' before or alongside VLAN assignment.
6
Assign interface to VLAN 20
Interface FastEthernet 0/1 actively forwards untagged traffic for VLAN 20
Executing 'switchport access vlan 20' under interface configuration mode completes the access port assignment.

Key Concept

Cisco IOS CLI Configuration Hierarchy for VLAN Creation and Access Port Binding
Question 154Question →

A network engineer is troubleshooting trunk connectivity between two switches and executes the following command on Switch-A:

Switch-A# show interfaces gigabitEthernet 1/0/2 trunk

Port Mode Encapsulation Status Native vlan
Gi1/0/2 auto n-802.1q trunking 99

Port VLANs allowed on trunk
Gi1/0/2 1-1005

Port VLANs allowed and active in management domain
Gi1/0/2 1,10,20,99

Port VLANs in spanning tree forwarding state and not pruned
Gi1/0/2 1,10,20

CDP emits periodic syslog messages warning of a native VLAN mismatch with the remote neighbor switch. Which statement accurately explains why VLAN 99 is absent from the spanning tree forwarding list and how untagged frames sent from Switch-A across this link are handled?

Show answer & explanation

Answer: Spanning Tree Protocol placed VLAN 99 into a PVID-inconsistency blocked state because the remote switch uses a different native VLAN, while Switch-A transmits VLAN 99 frames across the trunk without an 802.1Q tag.

Answer

Spanning Tree Protocol placed VLAN 99 into a PVID-inconsistency blocked state because the remote switch uses a different native VLAN, while Switch-A transmits VLAN 99 frames across the trunk without an 802.1Q tag.
On an IEEE 802.1Q trunk, traffic belonging to the configured native VLAN is transmitted untagged. When connected switches have mismatched native VLAN configurations, Cisco Per-VLAN Spanning Tree (PVST+/Rapid PVST+) detects a Port VLAN ID (PVID) inconsistency through BPDUs. To prevent Layer 2 bridging loops and unauthorized traffic leaking between different VLANs, STP blocks the mismatched native VLAN on the trunk interface, omitting it from the 'VLANs in spanning tree forwarding state' list.

Step-by-Step Solution

1
Analyze the 'show interfaces trunk' output fields.
Interface Gi1/0/2 has negotiated 802.1Q trunking (mode auto, status trunking) with Native VLAN 99. VLAN 99 is listed under allowed VLANs and active management domain VLANs.
Confirms that VLAN 99 exists in the local VLAN database and is permitted on the trunk allowed list.
2
Compare active management VLANs against spanning tree forwarding VLANs.
VLAN 99 is present in the active management domain (1, 10, 20, 99) but missing from the spanning tree forwarding state list (1, 10, 20).
Identifies that Spanning Tree Protocol (STP) has placed VLAN 99 into a blocked state.
3
Evaluate the impact of the CDP native VLAN mismatch warning on 802.1Q trunk operations.
When native VLANs differ across an 802.1Q trunk link, PVST+/Rapid PVST+ detects a PVID inconsistency via BPDUs and puts the native VLAN into a PVID-inconsistency blocking state. Per IEEE 802.1Q standards, frames originating from the local native VLAN (VLAN 99) are transmitted without an 802.1Q tag.
Connects the symptoms of the syslog warning to STP blocking mechanics and 802.1Q tagging behavior.

Key Concept

802.1Q Native VLAN Untagged Framing and STP PVID Inconsistency Blocking
Question 155Question →

An engineer is evaluating Layer 2 discovery protocol operations on a Cisco Catalyst switch connected to multi-vendor infrastructure. The switch is running the following active configuration:

text lldp run ! interface GigabitEthernet1/0/12 description Link to Non-Cisco Switch no cdp enable lldp transmit lldp receive ! interface GigabitEthernet1/0/24 description Link to VoIP Phone cdp enable no lldp transmit

During a network audit, the engineer issues the command `show lldp neighbors detail` and receives the following partial CLI output:

text ------------------------------------------------ Local Interface: Gi1/0/12 Chassis id: 0021.a012.3456 Port id: Eth1/1 Port Description: Ethernet1/1 System Name: SW-CORE-NEXUS System Description: Cisco Nexus Operating System (NX-OS) Software Time remaining: 105 seconds System Capabilities: Bridge, Router Enabled Capabilities: Bridge Management Addresses: IP: 10.1.100.2 Auto Negotiation: supported, enabled Physical media capabilities: 1000baseT(FD) Media Attachment Unit Type: 30 VLAN ID: 10

Which two conclusions accurately describe the protocol behavior and neighbor state for this switch based on the configuration and command output?

Select all that apply

Show answer & explanation

Answer: The local interface GigabitEthernet1/0/12 is successfully processing IEEE 802.1AB Type-Length-Value (TLV) data frames from the remote neighbor SW-CORE-NEXUS.; Interface GigabitEthernet1/0/24 will fail to transmit LLDP Data Units (LLDPDUs) to the connected VoIP phone, but it will continue sending CDP advertisements.

Answer

The local interface GigabitEthernet1/0/12 is processing IEEE 802.1AB Type-Length-Value (TLV) frames, and interface GigabitEthernet1/0/24 will refrain from transmitting outbound LLDP frames while retaining active CDP transmission.
LLDP relies on IEEE 802.1AB standard TLVs to exchange information between multi-vendor devices, which is demonstrated by the detailed attributes shown for SW-CORE-NEXUS on GigabitEthernet1/0/12. Furthermore, interface GigabitEthernet1/0/24 explicitly disables LLDP transmissions via 'no lldp transmit' while keeping CDP active via 'cdp enable'.

Step-by-Step Solution

1
Analyze interface GigabitEthernet1/0/12 configuration and protocol standard.
Interface Gi1/0/12 has CDP disabled and LLDP enabled ('lldp transmit' and 'lldp receive'). LLDP operates under IEEE 802.1AB using TLVs.
Verify standard protocol characteristics for LLDP neighbor discovery.
2
Evaluate interface GigabitEthernet1/0/24 interface commands.
'no lldp transmit' suppresses outgoing LLDP messages on Gi1/0/24, while 'cdp enable' maintains active CDP outbound frames.
Determine granular protocol control per interface.
3
Compare default CDP vs. LLDP holdtime timers against the CLI output.
CDP default holdtime is 180 seconds, while LLDP default holdtime is 120 seconds. Output shows 'Time remaining: 105 seconds', confirming a 120-second starting value for LLDP.
Differentiate default timer parameters between CDP and LLDP.

Key Concept

Layer 2 Discovery Protocol (CDP and LLDP) Operation, IEEE 802.1AB TLV Structure, and Per-Interface Control
Question 156Question →

Two Cisco Catalyst switches, SW1 and SW2, are connected via their GigabitEthernet0/1 interfaces. SW1 is configured with `switchport mode dynamic desirable`, `switchport trunk native vlan 20`, and `switchport trunk allowed vlan 10,20,30`. SW2 is configured with default DTP settings (`switchport mode dynamic auto`), `switchport trunk native vlan 1`, and `switchport trunk allowed vlan 10,20,40`. Which of the following statements accurately describe the operational status and traffic behavior across this interswitch link? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: The link operational state becomes an 802.1Q trunk because Dynamic Trunking Protocol (DTP) dynamic desirable mode on SW1 successfully negotiates with dynamic auto mode on SW2.; Traffic transmitted across the link for VLAN 10 is tagged with an explicit 4-byte 802.1Q header containing VLAN ID 10.

Answer

The operational state becomes an 802.1Q trunk due to successful DTP negotiation between dynamic desirable and dynamic auto modes, and traffic for VLAN 10 will carry a standard 4-byte 802.1Q tag header across the trunk link.
The combination of dynamic desirable on one end and dynamic auto on the other causes DTP to successfully negotiate an operational 802.1Q trunk. For any tagged VLAN allowed across the link that is not designated as native (such as VLAN 10), 802.1Q inserts a standard 4-byte field into the Ethernet frame header.

Step-by-Step Solution

1
Analyze Dynamic Trunking Protocol (DTP) operational mode interaction.
SW1 (dynamic desirable) actively sends DTP frames to negotiate trunking. SW2 (dynamic auto) listens and agrees to trunk, resulting in an operational trunk link.
Dynamic desirable + dynamic auto always yields an operational trunk link.
2
Evaluate IEEE 802.1Q tagging behavior for non-native allowed VLANs.
VLAN 10 is allowed on both sides and is non-native for both switches. Frames belonging to VLAN 10 are inserted with an explicit 4-byte 802.1Q header containing the VLAN ID.
Standard 802.1Q trunking tags all non-native VLAN traffic.
3
Evaluate native VLAN processing during mismatches.
SW1 sends VLAN 20 untagged (its native VLAN), while SW2 expects VLAN 1 untagged. Neither switch automatically tags its native VLAN unless globally configured via 'vlan dot1q tag native'. Mismatched native VLAN configuration leads to STP PVID inconsistencies, but does not alter local untagged frame generation.
Native VLAN configuration dictates local untagged frame transmission rules independently on each side.

Key Concept

802.1Q Interswitch Trunking Negotiation and Frame Tagging Mechanics
Estimated Time:2m 0s
Question 157Question →

A network administrator configures a Cisco Catalyst switch with a new VLAN and assigns an access port using the following command sequence:

Switch(config)# vlan 50
Switch(config-vlan)# name HR_Data
Switch(config-vlan)# exit
Switch(config)# interface fastEthernet 0/15
Switch(config-if)# switchport mode access
Switch(config-if)# switchport access vlan 50

Several weeks later, another engineer executes the command 'no vlan 50' in global configuration mode to remove VLAN 50 from the switch. What is the immediate operational state and forwarding behavior of port FastEthernet 0/15 after VLAN 50 is deleted?

Show answer & explanation

Answer: The port remains configured for VLAN 50, but becomes inactive and drops all incoming and outgoing frames.

Answer

The port remains configured for VLAN 50, but becomes inactive and drops all incoming and outgoing frames.
When a VLAN is deleted from a Cisco switch using the global configuration command 'no vlan <id>', the switch does not modify interface-level configuration commands. Interfaces previously assigned to that VLAN retain their 'switchport access vlan <id>' setting. However, because the target VLAN no longer exists in the Layer 2 VLAN table, the switchport becomes inactive and cannot forward frames until the VLAN is re-created globally or the port is reassigned to an existing active VLAN.

Step-by-Step Solution

1
Analyze interface configuration retention upon VLAN deletion in Cisco IOS.
Removing a VLAN globally with 'no vlan <id>' removes the VLAN entry from the VLAN database (vlan.dat), but does not alter the running configuration of interfaces configured with 'switchport access vlan <id>'.
Interface configuration commands and global VLAN database definitions operate independently.
2
Determine the operational forwarding state of an interface assigned to a non-existent VLAN.
Because the assigned access VLAN no longer exists in Layer 2 forwarding tables, the switchport becomes inactive and fails to forward ingress or egress traffic for attached hosts.
A switchport cannot forward Layer 2 frames unless its configured access VLAN actively exists in the switch's VLAN database.

Key Concept

Access Port Behavior upon VLAN Deletion
Question 158Question →

An engineer executes the `show interfaces trunk` command on a Cisco Catalyst switch interface GigabitEthernet0/2 and observes the following output:

text
Port Vlans allowed on trunk
Gi0/2 10,20,30

Port Vlans allowed and active in management domain
Gi0/2 10,20

Port Vlans in spanning tree forwarding state and not pruned
Gi0/2 10

Which condition explains why VLAN 30 is listed as allowed on the trunk, but is missing from the list of active VLANs in the management domain?

Show answer & explanation

Answer: VLAN 30 has not been created in the local VLAN database of the switch.

Answer

VLAN 30 has not been created in the local VLAN database of the switch.
In Cisco IOS, `show interfaces trunk` divides VLAN status into three operational categories. The first list shows administratively allowed VLANs (`switchport trunk allowed vlan`). The second list shows VLANs that are both administratively allowed AND present in the local switch VLAN database (`vlan <id>`). Because VLAN 30 appears in the first list but not the second, VLAN 30 has not been defined globally in the local switch VLAN database.

Step-by-Step Solution

1
Analyze the 'Vlans allowed on trunk' output section
VLANs 10, 20, and 30 are configured under the interface `switchport trunk allowed vlan` command.
This section displays the administrative list of allowed VLANs configured on the interface.
2
Analyze the 'Vlans allowed and active in management domain' section
VLAN 30 is absent from this list.
To be active in the management domain, a VLAN must exist in the switch's local VLAN database (`vlan 30`) and not be in a suspended state.
3
Deduce the root cause of the missing VLAN entry
VLAN 30 has not been created using the `vlan 30` global configuration command on the local switch.
Configuring a VLAN in the interface allowed list without creating the VLAN in global configuration prevents the switch from tagging or forwarding frames for that VLAN.

Key Concept

802.1Q Trunk Allowed vs Active VLAN Operation
Question 159Question →

Which two statements correctly describe IEEE 802.1Q trunking operational behavior on Cisco Catalyst switches? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: By default, Ethernet frames belonging to the configured native VLAN are transmitted across the trunk link without an 802.1Q header tag.; An 802.1Q header inserts 4 bytes into the Ethernet frame, which includes a 12-bit field dedicated to identifying the VLAN ID.

Answer

IEEE 802.1Q sends native VLAN traffic untagged across trunk links by default, and encapsulates tagged frames using a 4-byte header containing a 12-bit VLAN ID field.
IEEE 802.1Q trunking forwards native VLAN frames untagged by default. For all other VLANs, it inserts a 4-byte tag into the Ethernet header which incorporates a 12-bit VLAN Identifier.

Step-by-Step Solution

1
Identify standard 802.1Q frame structure and tagging rules.
Tagged frames receive a 4-byte tag containing a 12-bit VLAN ID, while frames on the native VLAN are forwarded untagged across the link by default.
802.1Q specifies untagged frame delivery for native VLAN traffic to ensure compatibility.
2
Examine the impact of configuring PortFast on switch-to-switch links.
PortFast skips STP listening and learning states, which can cause temporary Layer 2 loops if configured on interswitch trunk ports.
PortFast is designed strictly for access ports connected to end-user devices.
3
Analyze switch behavior when a native VLAN mismatch occurs across a trunk.
Traffic leaks across VLAN boundaries and CDP/STP generates warning logs, but the switch keeps the trunk operational rather than disabling the port.
Cisco switches flag PVID inconsistencies without automatically placing the interface into an err-disabled state.

Key Concept

802.1Q Frame Tagging and Trunk Operations
Estimated Time:1m 0s
Question 160Question →

An engineer captures traffic on a point-to-point trunk link between two switches. Switch-1 is configured with `switchport trunk native vlan 10`, while Switch-2 is configured with `switchport trunk native vlan 20`. When Switch-1 transmits untagged frames originating from VLAN 10 across the trunk link, how does Switch-2 process these frames upon ingress, and what operational issue occurs?

Show answer & explanation

Answer: Switch-2 assigns the received untagged frames to VLAN 20, resulting in cross-VLAN traffic leakage, while CDP continuously reports a native VLAN mismatch.

Answer

Switch-2 assigns the received untagged frames to VLAN 20, resulting in cross-VLAN traffic leakage, while CDP continuously reports a native VLAN mismatch.
Under 802.1Q trunking rules, native VLAN frames are transmitted untagged. When Switch-1 forwards VLAN 10 frames across the trunk without an 802.1Q tag, Switch-2 accepts the untagged frames and assigns them to its own configured native VLAN (VLAN 20). This leads to unintended cross-VLAN traffic leakage between VLAN 10 and VLAN 20. Additionally, CDP detects this discrepancy by exchanging native VLAN details in TLVs and regularly issues syslog warnings.

Step-by-Step Solution

1
Analyze Switch-1 egress processing for native VLAN 10
Frames originating from VLAN 10 are transmitted untagged across the 802.1Q trunk because VLAN 10 matches Switch-1's native VLAN configuration.
According to IEEE 802.1Q specifications, frames belonging to the configured native VLAN are sent across a trunk link without inserting a 4-byte VLAN tag header.
2
Analyze Switch-2 ingress processing for untagged frames
Switch-2 receives the untagged frames and maps them directly into its own native VLAN, which is VLAN 20.
When an 802.1Q trunk interface receives an untagged frame, it automatically assigns that frame to whichever VLAN is designated as native on that local receiving interface.
3
Determine operational impact and diagnostic behavior
Cross-VLAN traffic leakage occurs between VLAN 10 on Switch-1 and VLAN 20 on Switch-2, and CDP logs native VLAN mismatch notifications.
A native VLAN mismatch breaks logical isolation between different VLANs and triggers warning messages via CDP native VLAN TLV exchange.

Key Concept

802.1Q Native VLAN Ingress Processing and Mismatch Behavior
Estimated Time:2m 0s
PreviousPage 8 / 20Next
Network Access Practice Questions — Cisco CCNA — Page 8 | Examkin