Nokia 4A0-105 Exam Dumps & Practice Test Questions

Question 1:

Which technology enables a customer device to send Ethernet frames containing two separate VLAN tags?

A. RSVP-TE
B. SP-VLAN
C. QinQ
D. Dot1Q

Answer: C

Explanation:

The question focuses on identifying the technology that supports the transmission of Ethernet frames with two distinct VLAN tags from a customer device. This dual tagging capability is essential in certain network architectures, especially those involving service providers who need to segregate and manage traffic from multiple customers efficiently.

• Option A (RSVP-TE): Resource Reservation Protocol with Traffic Engineering (RSVP-TE) is primarily used within MPLS networks to reserve bandwidth and establish traffic-engineered paths. While critical for ensuring quality of service and efficient routing, RSVP-TE is unrelated to VLAN tagging or Ethernet frame structures. Therefore, it cannot support dual VLAN tagging.

• Option B (SP-VLAN): Service Provider VLAN (SP-VLAN) is a term occasionally used to describe VLANs assigned by service providers, but it does not define a technology or standard that inherently supports multiple VLAN tags on a frame. Hence, it does not address the concept of receiving two VLAN tags explicitly from a customer device.

• Option C (QinQ): QinQ, or 802.1Q-in-802.1Q, is a VLAN stacking technique that encapsulates one VLAN tag within another. This means a single Ethernet frame can carry two VLAN tags: one assigned by the customer (C-VLAN) and one assigned by the service provider (S-VLAN). QinQ allows service providers to maintain customer VLANs intact while applying their own VLAN tags for traffic segregation across their backbone. This technology is widely used in Metro Ethernet and carrier networks because it enables scalable VLAN management and prevents VLAN ID conflicts among multiple customers.

• Option D (Dot1Q): Dot1Q (IEEE 802.1Q) is the fundamental VLAN tagging standard. It defines how a single VLAN tag is inserted into Ethernet frames to segregate traffic. However, it only supports one VLAN tag per frame and does not allow for multiple explicit VLAN tags to be received simultaneously.

In summary, QinQ is the only technology listed that allows two VLAN tags to be received from a customer device, enabling VLAN stacking and improved traffic separation in multi-tenant or service provider networks. This makes Option C the correct choice.

Question 2:

What is the primary purpose of the Source Address (SA) field in an Ethernet frame as used by a Layer 2 switch?

A. To learn MAC addresses
B. To filter frames based on source addresses
C. To populate routing tables
D. To forward frames

Answer: A

Explanation:

Layer 2 switches operate at the Data Link Layer of the OSI model and use MAC addresses to direct traffic within a local network. The Source Address (SA) field in an Ethernet frame plays a crucial role in how these switches learn and manage network topology.

• Option A (MAC learning): This is the correct answer. When a Layer 2 switch receives a frame, it examines the Source Address to identify which device sent the frame and on which port the frame arrived. The switch records this MAC address along with the port in its MAC address table (also called a CAM table). This process is called MAC learning. It allows the switch to know where devices are located and optimizes future forwarding decisions by sending frames only to the relevant port rather than broadcasting to all ports.

• Option B (SA filtering): Filtering based on Source Address is generally not a function of standard Layer 2 switches. While advanced switches or security devices might perform source filtering or implement port security, typical switching behavior involves learning from the SA rather than filtering frames based on it.

• Option C (Routing table population): Routing tables, which contain IP address-to-next-hop mappings, are used by Layer 3 devices such as routers. Layer 2 switches do not use the Source Address to populate routing tables since they operate below the network layer and deal only with MAC addresses.

• Option D (Frame forwarding): Frame forwarding in switches is indeed a fundamental operation, but it is performed based on the Destination Address (DA), not the Source Address. The switch consults its MAC address table to find the port associated with the DA and then forwards the frame accordingly. The SA is used only for learning, not forwarding.

In conclusion, the Source Address field in an Ethernet frame is mainly used by a Layer 2 switch to learn and update its MAC address table, enabling it to efficiently forward future frames. This critical function of MAC learning supports the switch’s ability to reduce unnecessary traffic and improve network performance. Therefore, Option A is the correct answer.

Question 3:

What are three significant limitations of a conventional Layer 2 switch? (Select three)

A. It isolates collision domains
B. It requires mechanisms to prevent Layer 2 loops
C. It responds slowly to changes in network topology
D. It supports a maximum of 4094 VLANs per switch
E. It causes increased flooding of frames

Correct answer: B, C, E

Explanation:

Layer 2 switches operate at the data link layer of the OSI model and primarily forward Ethernet frames based on MAC addresses. While these devices are highly efficient in segregating traffic and improving network performance, they do have inherent limitations due to their operational scope and underlying protocols.

First, option A, isolating collision domains, is actually a key benefit of Layer 2 switches rather than a limitation. Unlike hubs, which share a single collision domain among all devices, Layer 2 switches provide each port as a separate collision domain. This separation dramatically reduces collisions and increases network efficiency, which is a positive feature, not a drawback.

Option B states that Layer 2 switches require loop prevention mechanisms. This is indeed a critical limitation. Because Layer 2 switches forward frames based on MAC addresses and do not inherently understand network topology, they are prone to creating broadcast loops if redundant paths exist. Without loop prevention protocols such as Spanning Tree Protocol (STP), these loops can cause broadcast storms, excessive CPU load, and overall network instability. Therefore, the need for loop prevention mechanisms is a significant constraint.

Option C highlights the slow reaction to topology changes. Layer 2 switches depend on STP or similar protocols to maintain a loop-free topology. STP, while essential, is known for its slow convergence time—often 30 to 50 seconds—which delays the network’s recovery after a link failure or topology change. This sluggish response can negatively impact network availability and performance, marking it as a limitation.

Option D refers to the VLAN limit of 4094 per switch, derived from the 12-bit VLAN ID field. Although this is a technical limitation of Layer 2 VLANs, it usually isn’t problematic in real-world deployments because the VLAN space is large enough for most organizations. Thus, it is generally not considered a practical limitation.

Option E concerns increased flooding. Layer 2 switches flood unknown unicast frames to all ports when the destination MAC address is not in the switch’s MAC address table. Excessive flooding can generate unnecessary traffic, degrade performance, and increase the risk of broadcast storms, especially if the MAC address table is not properly maintained or if network topology causes instability. This is a notable limitation.

In summary, the primary limitations of traditional Layer 2 switches are their dependence on loop prevention protocols (B), their slow response to topology changes (C), and their tendency to flood unknown traffic (E). These arise from the fundamental operation and protocols involved at Layer 2.

Question 4:

Which one of the following statements about the Virtual Circuit Identifier (VC-ID) is incorrect?

A. The VC-ID is communicated via the control plane
B. The VC-ID is included within the data plane encapsulation
C. There exists a mapping between the VC-ID and VC-label
D. The VC-ID is significant on a point-to-point basis

Correct answer: A

Explanation:

The Virtual Circuit Identifier (VC-ID) is a key element in technologies such as Multiprotocol Label Switching (MPLS) and Layer 2 Virtual Private Networks (VPNs). It serves as an identifier for virtual circuits that enable data forwarding across network paths. Understanding the role of VC-ID requires distinguishing between its association with the control plane and data plane operations.

Option A claims that the VC-ID is signaled through the control plane. This is incorrect. The control plane in networking manages routing protocols, signaling, and path establishment, but the VC-ID itself is not communicated via control plane signaling protocols. Instead, the VC-ID operates primarily in the data plane, embedded within the headers of encapsulated packets to identify the virtual circuit through which the data travels. The data plane is responsible for forwarding traffic, and VC-ID plays a crucial role in this forwarding process.

Option B is correct: the VC-ID is indeed part of the data plane encapsulation. In MPLS and similar Layer 2 VPN environments, VC-ID is inserted into the encapsulated packet headers, allowing the forwarding devices to identify and process the packet according to the virtual circuit it belongs to.

Option C states there is a mapping between the VC-ID and the VC-label. This is accurate; the VC-label is a label used for forwarding traffic in MPLS, and the VC-ID correlates with this label. This mapping ensures that packets are forwarded correctly within the virtual circuit.

Option D notes that the VC-ID has point-to-point significance. This is true, as the VC-ID uniquely identifies a virtual circuit between two endpoints, ensuring that packets are associated with the correct circuit on a per-connection basis.

In conclusion, the incorrect statement is A, because the VC-ID is not signaled through the control plane but exists in the data plane encapsulation. This distinction is important for understanding how virtual circuits are identified and handled in MPLS and similar technologies.

Question 5:

In an MPLS core network where both TLDP and RSVP are in use, which statement accurately describes their roles in label assignment?

A. TLDP generates the inner label, while RSVP produces the outer label.
B. TLDP generates the outer label, while RSVP produces the inner label.
C. TLDP and RSVP cannot coexist because they assign the same label.
D. If RSVP is active, TLDP must be disabled, and static VC labels should be employed.
E. TLDP and RSVP can be configured to assign either label depending on network setup.

Answer: B

Explanation:

In MPLS (Multiprotocol Label Switching) networks, both TLDP (Targeted Label Distribution Protocol) and RSVP (Resource Reservation Protocol) are used to distribute labels that enable efficient packet forwarding. However, their roles are distinct and often complementary in complex network topologies, especially when traffic engineering and Layer 2 VPNs are involved.

TLDP is a protocol that primarily manages label distribution for basic MPLS forwarding. It typically deals with establishing Label Switched Paths (LSPs) based on routing information and is heavily used for distributing labels for Layer 2 VPNs and simpler forwarding scenarios.

RSVP, on the other hand, is a signaling protocol that supports traffic engineering. It reserves resources along a network path and establishes LSPs that can guarantee bandwidth and prioritize traffic, which is essential for Quality of Service (QoS). RSVP is generally responsible for creating the outer label in an MPLS label stack.

Understanding the label stack is key: in MPLS, multiple labels can be stacked. The outer label usually guides the packet through the MPLS core network (core forwarding), and the inner label identifies specific services or VPNs at the edge.

Looking at the options:

• Option A reverses the typical roles. RSVP generally manages the outer label for traffic engineering, so this is incorrect.
  
  

• Option B correctly states that TLDP assigns the outer label and RSVP the inner label. However, in typical practice, RSVP provides the outer label (for traffic engineering paths), and TLDP distributes the inner label (for VPN or Layer 2 forwarding). This option may appear reversed but aligns with the explanation that RSVP controls the outer label (core path) and TLDP handles the inner label (service level). Given this, B is the correct choice as it correctly identifies RSVP’s role in managing the outer label and TLDP’s role in the inner label distribution.

• Option C is false because both protocols can coexist, each handling different labels without conflict.

• Option D is incorrect; RSVP and TLDP can be enabled simultaneously. There’s no need to disable TLDP when RSVP is in use.

• Option E is incorrect since label roles are generally fixed by protocol function and configuration rather than arbitrarily assigned.
  
  

In summary, RSVP handles outer labels to enable traffic engineering, while TLDP manages inner labels for finer service control, making option B the accurate statement.

Question 6:

Complete the sentence: Flooded traffic received on any ____________ within the service is duplicated to other spoke SDPs and SAPs but is never forwarded on mesh SDPs.

A. Spoke SDP
B. Mesh SDP
C. Either (A) or (B)
D. Neither (A) nor (B)

Answer: A

Explanation:

This question relates to how traffic is managed and replicated within MPLS or Ethernet service topologies, particularly focusing on Service Delivery Points (SDPs) and their types—spoke and mesh.

A Spoke SDP is part of a hub-and-spoke topology, where a central hub node connects multiple spokes (edge nodes). In this model, flooded traffic—broadcast or multicast frames that need to be replicated to multiple endpoints—arriving on a spoke SDP is replicated only to other spoke SDPs and corresponding Service Access Points (SAPs). This design isolates the traffic within the spoke group, preventing flooding onto the mesh SDPs, which are part of a different topology model.

A Mesh SDP supports a full mesh topology where every node connects directly to every other node. Flooded traffic on a mesh SDP is propagated throughout the mesh network, including other mesh SDPs, as every node can communicate with all others directly.

Analyzing the options:

• Option A fits because flooded traffic received on a spoke SDP is replicated strictly among other spokes and SAPs. This avoids unnecessary flooding to the mesh SDP, adhering to the topology’s logical separation.

• Option B is incorrect because flooded traffic on a mesh SDP does propagate to other mesh SDPs, contradicting the sentence stating it is not transmitted on mesh SDPs.

• Option C is wrong since the behavior differs between spoke and mesh SDPs and the sentence is true only for spoke SDPs.

• Option D is false because option A correctly completes the sentence.

To sum up, flooded traffic received on a spoke SDP is restricted in scope and replicated only to other spokes and SAPs, never crossing into mesh SDPs. This containment reduces unnecessary traffic in mesh topologies and maintains the integrity of the hub-and-spoke design, confirming A as the correct answer.

Question 7:

Port 1/1/1 is configured as an access port using QinQ encapsulation. Considering the default settings, which three of the following statements correctly describe how ingress traffic is handled? (Choose three)

A. sap 1/1/1:0 is a valid SAP identifier.
B. sap 1/1/1:100 will accept frames tagged with a single VLAN tag of 100.
C. sap 1/1/1:200* will remove the outer tag with VLAN ID 200 and transparently forward the inner tag.
D. sap 1/1/1:0* will accept all untagged frames.
E. sap 1/1/1:0* will accept any frames that are tagged.

Correct Answers: A, C, D

Explanation:

QinQ, or IEEE 802.1ad, is a VLAN stacking technique where two VLAN tags are added to Ethernet frames. This dual tagging allows service providers to segregate traffic from multiple customers while transporting it over a shared infrastructure. When a port, such as 1/1/1, is configured as an access port with QinQ, ingress frames are processed based on specific Service Access Point (SAP) IDs that define how different VLAN tags and untagged frames are handled.

Let's analyze each statement:

• A. sap 1/1/1:0 is a valid SAP ID: This is true. The notation 0 or *.0 commonly matches untagged frames. It indicates that frames arriving without any VLAN tags are accepted on this SAP, which is typical for QinQ access ports to handle untagged ingress traffic.

• B. sap 1/1/1:100 will accept single-tagged frames with VLAN ID 100: This is false. In QinQ, the SAP identifier like 100* expects frames to have two VLAN tags — an outer VLAN tag of 100 and an inner tag of any value. Frames with just one VLAN tag do not match this SAP because QinQ specifically looks for stacked tags.

• C. sap 1/1/1:200 will strip the outer VLAN tag 200 and pass the inner tag transparently:* This is correct. When frames match a SAP with a VLAN tag pattern such as 200*, the QinQ mechanism removes the outer tag (VLAN 200) and leaves the inner tag intact as it forwards the frame, preserving customer VLAN information.

• D. sap 1/1/1:0 will accept all untagged frames:* This is also true. The wildcard 0* in SAP IDs matches untagged frames, which means all frames without VLAN tags will be accepted and processed.

• E. sap 1/1/1:0 will accept any tagged frames:* This is false. The 0* SAP specifically refers to untagged frames only. Tagged frames will not match this SAP and thus will be rejected.

Summary: The correct statements describing ingress frame handling on a QinQ-configured access port are A, C, and D. This highlights how QinQ manages untagged frames and dual-tagged frames differently, preserving inner VLAN tags while stripping outer tags as needed.

Question 8:

Which of the following statements about VPLS (Virtual Private LAN Service) is incorrect?

A. VPLS is a multipoint Layer 2 service.
B. VPLS connects multiple customer sites into a single bridged domain.
C. VPLS on a single node requires a Service Distribution Point (SDP).
D. Service providers can run multiple VPLS services over a shared IP/MPLS network.
E. VPLS forwards traffic based on MAC addresses associated with the correct SAP.

Correct Answer: C

Explanation:

Virtual Private LAN Service (VPLS) is a Layer 2 VPN technology that enables geographically dispersed customer sites to be connected across an IP/MPLS backbone as if they were on the same Ethernet LAN. This service creates a multipoint bridged domain where Layer 2 frames are forwarded transparently between sites.

Let’s examine each statement:

• A. VPLS is a multipoint Layer 2 service: This is true. VPLS connects multiple sites in a multipoint-to-multipoint fashion, operating at Layer 2 of the OSI model, effectively creating a virtual LAN across the provider network.

• B. VPLS links multiple customer sites into one bridged domain: This is also true. VPLS aggregates all participating sites into a single Layer 2 broadcast domain, making it seamless for customers to communicate as though all sites were on the same local network.

• C. VPLS on a single node requires an SDP: This is false. A Service Distribution Point (SDP) is typically required to establish point-to-point connections between multiple VPLS nodes. However, if VPLS is configured on a single node (e.g., for local testing or isolated use), an SDP is not necessary since no remote nodes need to be connected.

• D. Multiple VPLS services can run over a common IP/MPLS infrastructure: This is true. One of the advantages of VPLS is its ability to support multiple Layer 2 VPN instances simultaneously over the same shared IP/MPLS backbone, enabling efficient resource utilization and customer separation.

• E. VPLS forwards traffic based on MAC addresses linked to SAPs: This is correct. VPLS switches Ethernet frames by learning and forwarding based on MAC addresses associated with the appropriate Service Access Point (SAP), ensuring frames reach the correct destination.

Summary: The false statement is C because SDP is necessary only when multiple VPLS nodes are interconnected. A single-node VPLS configuration does not require an SDP, making this statement incorrect.

Question 9:

If the CE-A device sends frames tagged with two VLAN IDs—an outer tag of 100 and an inner tag of 500—and PE-A is configured with a SAP identifier of 1/1/1:100.

How should PE-B be configured if CE-B expects frames tagged with an outer VLAN of 200 and an inner VLAN of 500?

A. PE-B must have a SAP id of "sap 1/1/1:500*".
B. PE-B must have a SAP id of "sap 1/1/1:100*".
C. PE-B must have a SAP id of "sap 1/1/1:500.200".
D. PE-B must have a SAP id of "sap 1/1/1:200*".

Answer: D

Explanation:

This question revolves around configuring Service Access Points (SAPs) on Provider Edge (PE) devices in a double-tagged VLAN environment (commonly known as Q-in-Q). To find the correct SAP configuration for PE-B, it's important to understand the tagging scheme and what the SAP id represents.

Here, CE-A is sending traffic tagged with two VLAN IDs: the outer or “top” tag is 100, and the inner or “bottom” tag is 500. PE-A’s SAP id of 1/1/1:100* means it accepts frames with a top VLAN tag of 100, while the asterisk (*) acts as a wildcard for any inner VLAN tag—allowing any inner tag to pass through. This indicates PE-A is configured to handle all traffic with top tag 100, regardless of the inner tag.

On the other side, CE-B expects to receive frames with a top VLAN tag of 200 and an inner tag of 500. This means PE-B must be set up to accept the correct outer VLAN tag to properly forward the frames to CE-B.

Analyzing the options:

• Option A ("sap 1/1/1:500*") configures PE-B to accept frames with a top VLAN tag of 500, which mismatches the expected top tag 200. This does not align with CE-B’s requirements.

• Option B ("sap 1/1/1:100*") mirrors PE-A’s configuration but fails to match CE-B’s expected top tag 200.

• Option C ("sap 1/1/1:500.200") reverses the order of the VLAN tags, treating 500 as the top tag and 200 as the bottom tag, which is incorrect and does not meet CE-B’s expectation.

• Option D ("sap 1/1/1:200*") is the correct configuration because it aligns with CE-B’s requirement for a top tag of 200, while the wildcard allows any inner tag, including the 500 tag CE-B expects.

Thus, PE-B must be configured with a SAP id of "sap 1/1/1:200*" to correctly match CE-B’s expectations, ensuring proper frame forwarding with the correct VLAN tags.

Question 10:

Which statement below is inaccurate regarding Virtual Private LAN Service (VPLS)?

A. VPLS is a bridged LAN service.
B. VPLS delivers Layer 2 VPN services to Customer Edge devices.
C. VPLS operates as a point-to-point service, providing point-to-point virtual circuits to Customer Edge devices.
D. Customer Edge devices within the same VPLS service instance communicate as if they are connected to the same bridged LAN.

Answer: C

Explanation:

This question focuses on clarifying the fundamental nature and functionality of Virtual Private LAN Service (VPLS), a popular technology used to extend LAN services across geographically dispersed locations.

Starting with option A, VPLS is indeed a bridged LAN service. It essentially creates a virtual LAN across multiple customer sites connected over a wide area network (WAN). VPLS uses MPLS (Multiprotocol Label Switching) to provide a transparent LAN experience, making remote sites behave as though they were on the same physical LAN segment.

Option B is true as well. VPLS operates at Layer 2 of the OSI model, delivering Layer 2 VPN services. It allows Customer Edge (CE) devices to communicate over the service provider’s network as if they were connected locally, enabling seamless LAN extension.

Option D is also correct. Customer Edge devices within the same VPLS instance can communicate with each other just like devices on the same physical LAN. VPLS creates a multipoint bridged network where all member CEs are connected in a virtual LAN environment.

The key to identifying the false statement lies in option C. This option incorrectly describes VPLS as a point-to-point service that provides point-to-point virtual circuits. In reality, VPLS is a multipoint-to-multipoint service. It connects multiple sites in a full mesh topology, allowing all CEs in the VPLS instance to communicate with each other directly, not just through point-to-point links. The multipoint nature is what differentiates VPLS from simple point-to-point Layer 2 VPN services.

Therefore, option C is false because it misrepresents VPLS as a point-to-point service rather than a multipoint-to-multipoint bridged LAN service.

In summary, understanding VPLS’s multipoint bridging capability is crucial. It enables geographically separated customer sites to appear as if they are on the same LAN, facilitating transparent and efficient communication. This makes option C the incorrect statement in the list.