Nokia 4A0-116 Exam Dumps & Practice Test Questions

Question 1:

Which of the following statements about MPLS (Multi-Protocol Label Switching) networks is incorrect?

A. MPLS employs signaling protocols to share labels among routers.
B. Label Switching Routers (LSRs) route traffic based on MPLS labels.
C. An MPLS Label Switched Path (LSP) operates as a two-way tunnel for data forwarding.
D. MPLS networks carry data transparently across the path from source to destination.

Correct Answer: C

Explanation:

To identify the incorrect statement regarding MPLS, let’s explore each option in the context of how MPLS works.

Option A states that MPLS uses signaling protocols for label exchange, which is true. Protocols like LDP (Label Distribution Protocol) and RSVP-TE (Resource Reservation Protocol – Traffic Engineering) are used in MPLS networks to advertise and manage labels between routers. This allows for efficient path setup and traffic engineering, key benefits of MPLS.

Option B is also correct. Label Switching Routers (LSRs) are core devices in an MPLS network that forward packets based solely on labels. These labels are inserted at the edge of the network and are used by the core routers to make fast forwarding decisions, avoiding the need for complex IP lookups.

Option C, however, is false and is the correct answer. An LSP in MPLS is not bi-directional by default. It is unidirectional, meaning it only supports data flow in a single direction—from the ingress router to the egress router. If bidirectional communication is required, two separate LSPs must be configured, one in each direction. This distinction is critical in understanding MPLS operations and traffic engineering.

Option D is true. One of the benefits of MPLS is that it enables transparent data transmission across a provider’s network. Once the data enters the MPLS domain, it is transported using labels without altering the original data packet, making the transmission seamless from the end-user’s perspective.

The key misunderstanding in Option C lies in assuming MPLS tunnels are inherently bidirectional. In reality, LSPs are built per direction, and this detail is essential for designing MPLS-based networks. Therefore, the false statement is C, making it the correct answer to this question.

Question 2:

Which of the following statements about Segment Routing SIDs (Segment Identifiers) is inaccurate?

A. A Node-SID is typically tied to a router's loopback or system interface.
B. Adjacency-SIDs are selected from the Segment Routing Global Block (SRGB).
C. A Prefix-SID may be assigned directly as a label or indirectly via an index.
D. Adjacency-SIDs are optional and may not require manual configuration.

Correct Answer: B

Explanation:

Segment Routing (SR) is a modern, scalable approach to traffic engineering that simplifies network operations. It uses SIDs (Segment Identifiers) to define forwarding paths through the network, with various SID types serving distinct roles.

Option A is accurate. A Node-SID uniquely identifies a router and is typically associated with its loopback interface. It represents a specific node in the network, allowing other routers to steer traffic toward that node.

Option B, however, is inaccurate and the correct answer. Adjacency-SIDs are not taken from the SRGB (Segment Routing Global Block). SRGB is a globally reserved pool of label values used for Prefix-SIDs and Node-SIDs. In contrast, Adjacency-SIDs are usually selected from a locally significant label space and are not globally advertised. This allows each router to define its own adjacency labels without relying on global coordination.

Option C is true. Prefix-SIDs can be configured either directly by assigning a specific label or indirectly through an index value that references an entry within the SRGB. This flexibility enables easier automation and scale in Segment Routing environments.

Option D is also valid. Adjacency-SIDs are often auto-generated by the router and do not always need manual configuration. They are used when traffic must follow a specific link between two adjacent nodes, especially in use cases where deterministic paths are essential.

The misconception in Option B is the assumption that Adjacency-SIDs come from the SRGB, when in fact, they use a separate local label pool. Understanding this distinction is vital in SR implementation. Thus, B is the false statement and the correct choice.

Question 3:

Which of the following statements about Segment Routing is incorrect?

A. Segment Routing tunnels do not require any path signaling for setup.
B. Intermediate nodes along the path do not need to store tunnel state information.
C. A link-state IGP distributes Segment Identifiers (SIDs) throughout the network.
D. For traffic-engineered tunnels, a single MPLS label is usually sufficient to define the path.

Correct Answer: D

Explanation:

Segment Routing (SR) introduces a simplified, scalable approach to traffic engineering and network routing, using a concept where the source node determines the path and encodes it directly in the packet as a list of segments. These segments are identified by Segment Identifiers (SIDs) and guide the packet through the network. Unlike traditional MPLS with RSVP-TE or LDP, SR does not depend on complex control plane signaling or per-flow state at each hop.

Let’s assess each option:

Option A: This is true. One of the hallmark advantages of SR is that it eliminates the need for signaling protocols like RSVP-TE or LDP to set up tunnels. The path is determined at the source node and embedded in the packet header using a list of SIDs. This stateless model reduces complexity and improves network scalability.

Option B: This is also true. In SR, intermediate routers do not maintain state for each tunnel or flow. Instead, they forward packets based on the SIDs encoded in the MPLS label stack. This design results in simpler operations and lower memory usage on transit routers.

Option C: True again. In Segment Routing, link-state Interior Gateway Protocols (IGPs) such as OSPF or IS-IS are used to advertise SIDs across the network. These protocols distribute routing and SID information in a way that all routers can understand the network topology and the segment routing information necessary for forwarding.

Option D: This statement is false and thus the correct answer. In the case of traffic engineering (TE)-constrained tunnels, SR does not typically use a single MPLS label. Instead, packets often carry a stack of multiple MPLS labels, each corresponding to a segment in the intended path. This segment list enables granular control over the path taken by a packet, allowing operators to meet specific performance requirements such as latency, bandwidth, or policy compliance.

To summarize, while SR offers many operational benefits by removing signaling and reducing state in the network, it still relies on multiple MPLS labels in traffic-engineered scenarios. This enables SR to deliver fine-tuned TE capabilities without the complexity of traditional MPLS mechanisms.

Question 4:

Which of the following statements about a Segment Routing Node-SID is incorrect?

A. A Node-SID can be directly assigned as an MPLS label.
B. A router advertises its Node-SID as a local SRGB and index only when it’s configured with an index.
C. Routers are not required to use the same Segment Routing Global Block (SRGB).
D. A Node-SID can be configured using an index.

Correct Answer: B

Explanation:

Segment Routing (SR) relies on Segment Identifiers (SIDs) to guide packets through the network. One critical type of SID is the Node-SID, which uniquely represents a specific router (node) in the topology. Node-SIDs are globally significant within the domain and are used to reach the corresponding router directly.

Let’s examine each statement:

Option A: This is correct. A Node-SID can indeed be mapped directly to an MPLS label. Each SID within the SR architecture corresponds to a forwarding instruction, and for MPLS data planes, these SIDs are encoded as labels. This direct mapping simplifies packet forwarding and avoids additional resolution steps.

Option B: This is false and is the correct answer. The Node-SID advertisement does not depend on whether the router is configured with an index. When a router is configured with a Node-SID, it advertises this SID in its IGP updates regardless of how the SID was defined (via index or label). The SID is mapped using the Segment Routing Global Block (SRGB), and this advertisement ensures that all routers in the domain understand how to reach the node. The key point is that advertisement occurs as long as the Node-SID is defined, not only when it’s configured with an index.

Option C: This is true. It is not required that every router in a network uses the same SRGB. While using a consistent SRGB across all routers simplifies label interpretation and troubleshooting, SR supports flexibility by allowing different routers to use different SRGBs. Each router must, however, maintain a consistent internal mapping between index and label.

Option D: This is also true. A Node-SID can be configured as an index value within the SRGB. This index is then used to derive the corresponding label. The index-based configuration is a common method for managing Node-SIDs because it makes label allocation systematic and predictable.

In conclusion, Option B is false because it incorrectly suggests that Node-SID advertisement depends on index configuration. In practice, Node-SIDs are advertised as part of IGP updates whenever they are assigned, regardless of the method used for configuration.

Question 5:

In OSPF-based Segment Routing, each opaque LSA includes a link-state ID where the first byte identifies the type of advertised information. 

Which of the following value-to-purpose mappings is incorrect?

A. Value 1 – Traffic Engineering
B. Value 4 – Router Information
C. Value 7 – SRGB Range
D. Value 8 – Extended Link Information

Correct Answer: C

Explanation:

When OSPF (Open Shortest Path First) is extended to support Segment Routing (SR), it uses opaque LSAs (Link-State Advertisements) to distribute SR-specific information. Each opaque LSA includes a link-state ID, and the first byte of this ID defines the type of information being advertised. These values are standardized and essential for routers to interpret and utilize SR data properly. Let’s analyze what each of these values truly represents.

Option A: Value 1 – Traffic Engineering
This is a valid association. A first-byte value of 1 is indeed used to represent Traffic Engineering (TE) information. This includes critical attributes such as bandwidth, delay, and administrative group values that help routers make intelligent forwarding decisions and optimize path selection.

Option B: Value 4 – Router Information
This is also correct. A value of 4 corresponds to the Router Information (RI) LSA, which advertises details about the originating router. This LSA is essential for distributing flags and capabilities—such as Segment Routing support—within the OSPF network.

Option C: Value 7 – SRGB Range
This is the incorrect association and thus the correct answer to the question. The Segment Routing Global Block (SRGB) is not associated with a first-byte value of 7. In reality, SRGB information is carried using a first-byte value of 3, which is typically encapsulated in the Prefix-SID TLV (Type-Length-Value) under the Prefix Opaque LSA. Therefore, saying that value 7 corresponds to SRGB is false.

Option D: Value 8 – Extended Link Information
This is accurate. The value 8 represents Extended Link Information, which contains more granular link attributes such as adjacency SIDs and link delay—vital for advanced TE and SR implementations.

To conclude, each opaque LSA in OSPF-SR uses a predefined value in the first byte of the link-state ID to indicate its purpose. Misidentifying these values can lead to configuration errors and failed protocol operations. Among the options listed, Option C incorrectly maps the value 7 to SRGB, when the correct value should be 3. Therefore, Option C is the false association.

Question 6:

When setting up IS-IS to enable Segment Routing, which of the following steps is NOT a required part of the configuration process?

A. Reserving an MPLS label range for Segment Routing
B. Enabling MPLS on interfaces participating in Segment Routing
C. Configuring the flooding scope for Segment Routing information
D. Defining the Segment Routing Global Block (SRGB) range

Correct Answer: C

Explanation:

Intermediate System to Intermediate System (IS-IS) is a widely used interior gateway protocol that supports Segment Routing (SR) by distributing segment-related data to all routers within a domain. While configuring IS-IS to operate with SR, administrators must follow certain essential steps to ensure proper label allocation, path computation, and routing behavior. However, not every possible configuration step is mandatory.

Let’s evaluate each of the listed actions.

Option A: Reserving an MPLS label range for Segment Routing
This step is required. Segment Routing depends on MPLS labels to represent segments. You must reserve a block of labels that will be used exclusively for SR-related tasks, typically drawn from the SRGB (Segment Routing Global Block). This allows consistent label interpretation across the network.

Option B: Enabling MPLS on interfaces used for Segment Routing
This is also mandatory. For routers to forward traffic based on SR labels, the participating interfaces must be enabled for MPLS. Without this, segment labels would be meaningless because the routers wouldn't know how to handle them on those interfaces.

Option C: Configuring the flooding scope for Segment Routing information
This is the correct answer because it is not required. While flooding scope controls how widely SR data (like Prefix-SIDs or Adjacency-SIDs) is advertised, it is more of a tuning parameter rather than a strict requirement. By default, SR information is already flooded throughout the IS-IS domain. Customizing the scope can improve scalability or performance in large-scale networks, but it is not essential for basic SR operation.

Option D: Defining the SRGB range
This step is essential. The SRGB defines the label space that routers use to assign and interpret segment IDs. Consistency in this range ensures that when one router assigns a label for a segment, all others interpret it correctly.

In summary, when configuring IS-IS to support Segment Routing, steps like setting the MPLS label range, enabling interfaces, and defining SRGB are critical. However, specifying the flooding scope is optional and does not hinder SR functionality. That makes Option C the right answer to this question.

Question 7:

Which type of OSPF type-10 Opaque LSA is responsible for advertising a router's local Segment Routing Global Block (SRGB)?

A. Extended Prefix Info
B. Router Info
C. Extended Link Info
D. Traffic Engineering Info

Answer: B

Explanation:

OSPF (Open Shortest Path First) is a widely used link-state routing protocol that supports extensions through Opaque LSAs. These Opaque LSAs (Link-State Advertisements) allow OSPF to transport additional information beyond what is required for traditional routing decisions. Type-10 Opaque LSAs, in particular, are link-local scope LSAs used to carry information that applies only to the local router or its direct neighbors.

One of the modern features supported by OSPF is Segment Routing (SR), which simplifies traffic engineering by encoding paths as sequences of segments. Each segment is typically represented by a label or identifier. To support Segment Routing, routers need to share their Segment Routing Global Block (SRGB)—a contiguous block of MPLS labels used for global segment identifiers.

The Router Information (RI) LSA, which is a type-10 Opaque LSA, is specifically designed to convey SR-related capabilities and attributes, including the router's local SRGB. This information helps other routers understand how labels are mapped to segments in the network, ensuring proper forwarding behavior across the domain.

Let’s evaluate the options:

• A. Extended Prefix Info: This is used to advertise detailed prefix-level data, especially in segment routing scenarios, but not the SRGB itself.

• B. Router Info: Correct. This advertisement type carries a router’s local SRGB, among other SR capabilities such as supported SID types and algorithms.

• C. Extended Link Info: While this type of LSA may provide additional link metrics or attributes, it does not convey SRGB details.

• D. Traffic Engineering Info: Typically related to type-9 Opaque LSAs used for traffic engineering extensions in OSPF, but not responsible for SRGB information.

In summary, the Router Information advertisement is used within OSPF type-10 Opaque LSAs to carry the router's local SRGB, along with other segment routing capabilities. This makes B the correct and most appropriate answer.

Question 8:

Which of the following is not something that a router must advertise when participating in Segment Routing?

A. Local Node-SID
B. Adjacency-SIDs
C. Support for SR-MPLS for IPv4 or IPv6, or SRv6
D. SRGB when SRv6 is configured

Answer: C

Explanation:

Segment Routing (SR) is a flexible and scalable method for source-based routing that allows the source of a packet to define its path through the network. It relies on segment identifiers (SIDs), which are distributed throughout the network so that routers can make forwarding decisions based on these SIDs.

When a router participates in SR, it needs to advertise specific types of SIDs and associated data so other routers in the network can route traffic accordingly. This information includes:

• Local Node-SID: This is a unique identifier representing the router itself. It is essential for segment routing operations because it allows routers to route packets to a specific node via the shortest path.

• Adjacency-SIDs: These identifiers represent links to directly connected neighbors. They are critical for precise traffic engineering, enabling routers to control path selection at a granular level.

• SRGB (Segment Routing Global Block): This is a range of labels reserved for segment routing. If a router is configured with SRv6 (Segment Routing using IPv6), it still must advertise its SRGB to define what label range or SID range it supports.

Now consider option C – “Support for SR-MPLS for IPv4 or IPv6, or SRv6”. While it is important for routers to be configured to support one of these segment routing data planes, this capability itself does not need to be advertised explicitly to other routers. What’s advertised is the actual operational data, such as Node-SIDs, Adjacency-SIDs, and SRGB. The support for a particular SR type (MPLS-based or SRv6) is part of configuration and operational capabilities, but not a mandatory advertised parameter.

• A. Local Node-SID: Must be advertised – Required

• B. Adjacency-SIDs: Must be advertised – Required

• C. Support for SR-MPLS for IPv4 or IPv6, or SRv6: Not required to be advertised – This is configuration, not advertised data

• D. SRGB when SRv6 is configured: Must be advertised – Required

Therefore, the correct answer is C, as it is not required to be advertised in the Segment Routing protocol.

Question 9:

Which of the following statements about Segment Routing (SR) tunnels is inaccurate?

A. A tunnel created using a Node-SID in Segment Routing follows the shortest IGP route.
B. Segment Routing tunnels can be built using multiple Node-SIDs.
C. Segment Routing tunnels may consist of both Node-SIDs and Adjacency-SIDs.
D. Intermediate routers in a Segment Routing tunnel always use the best IGP route to forward traffic.

Correct Answer: D

Explanation:

Segment Routing (SR) is an innovative approach to network routing that allows for flexible and programmable path control using a concept known as segments. These segments, encoded in the packet header, guide traffic through the network without requiring each hop to maintain detailed per-flow state. SR operates on top of an IGP such as OSPF or IS-IS and supports both Node-SIDs and Adjacency-SIDs to define forwarding behavior.

Option A is correct. A Node-SID is an identifier that maps to a specific node or router. When used alone in a segment list, it instructs the network to forward packets along the shortest IGP path to that node, based on the current topology and metric calculations. This behavior aligns with standard IGP functionality.

Option B is also correct. Segment Routing allows for the creation of paths using multiple Node-SIDs. This setup is often referred to as source routing, where the ingress router defines an explicit sequence of nodes (via Node-SIDs) through which the packet must traverse. This provides the network operator with more granular traffic steering capabilities.

Option C is accurate as well. Segment Routing supports combining Node-SIDs (which identify routers) and Adjacency-SIDs (which identify specific links between routers). By using both types, operators can achieve precise control over the path, ensuring packets not only reach specific nodes but also traverse specific interfaces or links, which is useful for traffic engineering.

Option D, however, is false and thus the correct answer. The statement that “intermediate routers always forward packets based on the best IGP path” is misleading in the context of Segment Routing. In SR, routers do not rely solely on the best IGP path when forwarding packets. Instead, they use the segment list embedded in the packet to make forwarding decisions. The segment list acts like a pre-defined set of routing instructions that may deviate from the shortest or most optimal IGP path to achieve traffic engineering goals such as load balancing, latency minimization, or avoiding congestion.

Therefore, the false statement is D, because Segment Routing does not require routers to follow the best IGP path—routing is controlled by the segment list provided by the ingress router.

Question 10:

Which of the following is NOT a primary objective of network traffic engineering?

A. Taking advantage of redundant paths within the network.
B. Minimizing the likelihood of traffic congestion across the infrastructure.
C. Designing traffic paths based on constraints like bandwidth or latency.
D. Always using the shortest available path to the destination.

Correct Answer: D

Explanation:

Traffic engineering is a strategic method used by network engineers to optimize how data traverses a network. The goal is to ensure performance, reliability, scalability, and efficient use of resources while accommodating various constraints and service requirements.

Option A reflects a valid goal of traffic engineering. Utilizing redundant links increases fault tolerance by ensuring alternate paths are available in the event of failures. Instead of letting these backup paths sit idle, traffic engineering can use them to balance loads dynamically or during peak demand periods, improving network efficiency.

Option B is another key aim of traffic engineering. Preventing or mitigating congestion is central to maintaining service quality. By monitoring real-time traffic and network utilization, routing decisions can be adjusted proactively to avoid bottlenecks, ensuring smoother and more reliable traffic flows.

Option C is also true. A critical aspect of traffic engineering is to define routes that respect specific constraints, such as required bandwidth, latency, jitter, or even administrative policies. Constraint-based routing is particularly useful in service provider environments where SLAs (Service Level Agreements) must be met.

Option D, on the other hand, is not typically a goal of traffic engineering and is therefore the correct answer. While shortest-path routing is a fundamental principle in traditional IGPs like OSPF or IS-IS, traffic engineering often deliberately chooses non-shortest paths to optimize overall network utilization or meet policy and performance requirements. For example, if the shortest path is congested or doesn’t meet latency guarantees, a longer but more efficient or less congested route might be preferred. Traffic engineering trades off between metrics like path length, bandwidth availability, or redundancy to meet global network objectives.

To summarize, shortest-path routing is a default behavior of routing protocols, but traffic engineering aims for optimized routing rather than shortest routing. Thus, D does not align with the true objectives of traffic engineering.