Cisco 350-501 Practice Test Questions, Exam Dumps

Practice Exams:

View All

350-501 Cisco Practice Test Questions and Exam Dumps

Question No 1:

Refer to the exhibit. P3 and PE4 are located at the edge of the service provider core and serve as ABR (Area Border Router) routers. The network architecture has aggregation areas on either side of the core. Based on this architecture, which of the following statements is accurate?

A. To ensure seamless MPLS functionality, the BGP route reflector feature should be disabled.
B. If each area operates its own IGP (Interior Gateway Protocol), BGP must facilitate an end-to-end MPLS LSP (Label Switched Path).
C. If each area operates its own IGP, the ABR routers must redistribute the IGP routing table into BGP.
D. To ensure seamless MPLS functionality, TDP (Tag Distribution Protocol) must be utilized as the label distribution protocol.

Answer:

The correct answer is C. If each area operates its own IGP, the ABR routers must redistribute the IGP routing table into BGP.

Explanation:

In the context of a service provider network using MPLS (Multiprotocol Label Switching), understanding how routing between different areas and autonomous systems functions is essential. The network described in the question involves multiple areas with separate IGPs, with the ABR routers (P3 and PE4) serving as the boundary between the aggregation areas and the service provider's core.

Let's break down each option to clarify why C is the correct answer.

Option A: "To support seamless MPLS, the BGP route reflector feature must be disabled."

This statement is incorrect. The BGP route reflector feature does not directly affect the operation of MPLS. MPLS relies on label distribution protocols (LDP or RSVP-TE), not the BGP route reflector mechanism. BGP route reflectors are used to reduce the number of BGP peering sessions in a large network and help maintain route consistency in BGP, but they do not interfere with the seamless operation of MPLS. MPLS can function seamlessly with or without the use of BGP route reflectors.

Thus, this option does not provide the correct answer for supporting seamless MPLS.

Option B: "If each area is running its own IGP, BGP must provide an end-to-end MPLS LSP."

This statement is partially correct but not entirely accurate. The relationship between BGP and MPLS LSPs (Label Switched Paths) is somewhat indirect in this case. While BGP can be used to distribute routes and can facilitate MPLS LSPs, the actual label distribution (and creation of LSPs) is handled by label distribution protocols like LDP or RSVP-TE, not BGP.

In a network where each area uses its own IGP, it is crucial that the IGPs are able to communicate, which can involve the use of BGP, especially when inter-area routing is required. However, BGP's primary role in MPLS is to exchange reachability information, not directly set up LSPs.

Therefore, this option doesn't fully capture the relationship between BGP and MPLS in this scenario.

Option C: "If each area is running its own IGP, the ABR routers must redistribute the IGP routing table into BGP."

This statement is correct. When each area in an MPLS network uses its own IGP (such as OSPF or EIGRP), the ABR routers at the boundary between the areas are responsible for exchanging routing information between the IGPs in the different areas and BGP.

For proper inter-area routing, the ABR routers must redistribute the routing information from the IGP into BGP so that other routers in the network can learn about the routes from the other areas. In the context of MPLS, BGP is often used to provide reachability for MPLS LSPs across the network. The ABR routers must ensure that the routing information from the IGPs in each area is propagated to BGP, allowing the labels to be properly distributed and ensuring that LSPs are established correctly.

This is why option C is the most accurate answer.

Option D: "To support seamless MPLS, TDP must be used as the label protocol."

This statement is incorrect. TDP (Tag Distribution Protocol) was one of the early label distribution protocols used in MPLS networks, but it is not the only option available, nor is it a mandatory protocol for seamless MPLS.

MPLS networks typically use LDP (Label Distribution Protocol) or RSVP-TE (Resource Reservation Protocol-Traffic Engineering) for label distribution. TDP is often used interchangeably with LDP, but LDP has become the more widely used and recommended protocol in modern MPLS networks.

Furthermore, the choice of label distribution protocol does not directly impact the seamless operation of MPLS; both LDP and RSVP-TE are capable of supporting MPLS functionality, depending on the network's specific requirements (such as traffic engineering or simplicity).

Thus, this option is also not the correct answer for ensuring seamless MPLS operation.

Detailed Explanation of Option C

In this network design, the ABR routers (P3 and PE4) are at the edge of the service provider core and serve as the connection points between different areas, with aggregation areas on either side. These ABRs play a crucial role in managing inter-area routing.

When each area uses its own IGP, the ABR routers must redistribute the routing information from the IGP into BGP. This allows BGP to carry routing information across different areas, ensuring that the correct labels are distributed for the MPLS LSPs (Label Switched Paths) to be established.

The redistribution process is necessary because BGP, which operates at the boundary of the areas, needs to be aware of all the available routes from each IGP to forward traffic properly. BGP then ensures that these routes are propagated across the network, allowing MPLS to function seamlessly by providing label distribution for traffic forwarding.

Without this redistribution, the routers in different areas would not be able to communicate effectively, and the MPLS LSPs would not be able to be set up correctly. This would disrupt the flow of data across the network, leading to network inefficiencies.

In summary, for this MPLS architecture to work effectively, the ABR routers must redistribute the IGP routing table into BGP, allowing for the seamless distribution of MPLS labels and ensuring that LSPs are established correctly across the network.

Question No 2:

In the context of EVPN (Ethernet VPN) technology, which component is similar to an EVPN instance?

A. Router Distinguisher
B. MPLS Label
C. IGP Router ID
D. VRF

Answer:

The correct answer is D. VRF (Virtual Routing and Forwarding).

Explanation:

Ethernet VPN (EVPN) is a powerful and scalable technology that provides a mechanism for interconnecting Ethernet segments across a wide area network (WAN). EVPN is often used in MPLS-based networks and is based on BGP (Border Gateway Protocol) to provide Layer 2 and Layer 3 VPN services. One of the key concepts of EVPN is the idea of an "instance" or "VPN instance," which helps in differentiating between multiple network services running on the same physical infrastructure.

To understand the correct answer to this question, we need to explore the concept of an EVPN instance in detail and see how it compares to other components in networking such as router distinguishers, MPLS labels, IGP router IDs, and VRFs.

Option A: Router Distinguisher

A router distinguisher (RD) is used in MPLS VPNs to make the route targets (RTs) unique by distinguishing different routing instances on a router. In an MPLS VPN, the RD is appended to an IP address to create a globally unique VPNv4 address. This ensures that the same IP address can be used in different VPNs without conflict. However, a router distinguisher is primarily used in MPLS VPNs and does not correlate directly with the concept of an EVPN instance, which is more about Layer 2 connectivity and multi-tenancy.

Thus, the router distinguisher is not analogous to an EVPN instance because it does not represent a virtualized forwarding context.

Option B: MPLS Label

An MPLS label is used in MPLS networks for label-based forwarding. MPLS labels are assigned to packets and used to forward them based on pre-established paths in the network. While MPLS labels are an essential component of traffic engineering and forwarding in MPLS networks, they do not serve the same purpose as EVPN instances. EVPN instances are used to define virtual network topologies and services, and MPLS labels help in forwarding packets through the network, but they are not directly related to the segmentation of the virtualized networks provided by EVPN.

Therefore, MPLS labels do not resemble an EVPN instance and are not the correct answer to this question.

Option C: IGP Router ID

The IGP router ID is a unique identifier for a router in an Interior Gateway Protocol (IGP) such as OSPF (Open Shortest Path First) or IS-IS (Intermediate System to Intermediate System). It is used to identify routers in the routing domain for purposes of exchanging routing information. While the IGP router ID is crucial for routing decisions and advertisements in an IGP domain, it does not have a direct analogy to an EVPN instance. An EVPN instance deals with virtualized forwarding and Layer 2 connectivity, whereas the IGP router ID is associated with routing in Layer 3.

Thus, the IGP router ID is not comparable to an EVPN instance.

Option D: VRF (Virtual Routing and Forwarding)

A VRF (Virtual Routing and Forwarding) instance is the most analogous component to an EVPN instance. A VRF is a technology that allows multiple instances of a routing table to exist on the same router, each isolated from the others. VRFs enable a single physical router to maintain separate routing tables for different customer networks or different network segments, which provides the ability to have overlapping IP addresses in each VRF. This is similar to how EVPN instances create separate virtual network environments within a single physical infrastructure.

In an EVPN deployment, each "EVPN instance" represents a virtual network that is independent and isolated from other networks. Just as VRFs isolate routing tables and maintain separation between different networks, EVPN instances perform similar functions by isolating traffic for different tenants or services while running over shared physical infrastructure. Therefore, VRF is the most appropriate comparison to an EVPN instance.

In summary, EVPN instances operate in much the same way as VRFs, offering a method to isolate traffic, maintain separate virtual network environments, and provide a scalable solution for Layer 2 and Layer 3 VPN services. Thus, the correct answer is D. VRF.

Why VRF is the Correct Answer

The EVPN architecture allows service providers to offer multi-tenant Layer 2 and Layer 3 VPNs. Each tenant or customer is typically assigned a virtual network context or instance. This "instance" is similar in concept to the way VRFs work in MPLS VPNs. Just like VRFs allow multiple virtualized routing instances on the same router, EVPN instances provide a similar capability for virtualized Layer 2 and Layer 3 networks within a shared MPLS or IP infrastructure.

The analogy between VRFs and EVPN instances is particularly strong because both serve to logically segment different customers or services in a scalable and efficient manner. For example, in a data center or enterprise network, an EVPN instance might be used to isolate traffic between different tenants or applications, just as a VRF would be used to isolate routing tables for different customer networks in an MPLS VPN scenario.

Both VRFs and EVPN instances are critical for providing scalable, multi-tenant services, making VRF the most appropriate comparison for an EVPN instance in this context.

Question No 3:

Why do Cisco MPLS Traffic Engineering (TE) tunnels require a link-state routing protocol?

A. The link-state database provides segmentation by area, which enhances the path-selection process.
B. The link-state database provides a data repository from which tunnel endpoints can dynamically select a source ID.
C. Link-state routing protocols use SPF (Shortest Path First) calculations that tunnel endpoints leverage to establish the tunnel.
D. The tunnel endpoints use the link-state database to evaluate the entire network topology and determine the best path.

Answer:

The correct answer is D. The tunnel endpoints use the link-state database to evaluate the entire network topology and determine the best path.

Explanation:

MPLS Traffic Engineering (MPLS TE) is a powerful technique used in modern service provider networks to optimize the utilization of network resources. MPLS TE enables the creation of explicit Label Switched Paths (LSPs) between different network nodes, which allows for better traffic management, congestion control, and optimized path selection. One of the critical components for implementing MPLS TE is the use of a link-state routing protocol. Let’s break down why a link-state routing protocol is required for MPLS TE tunnels and why option D is the correct answer.

MPLS TE and Link-State Routing Protocols

MPLS TE relies heavily on the underlying network topology and routing information to establish optimal paths for traffic flows. For effective traffic engineering, the network must have complete visibility of the topology, including link capacities, bandwidth availability, and potential congestion points. Link-state routing protocols like OSPF (Open Shortest Path First) and IS-IS (Intermediate System to Intermediate System) are used to exchange and maintain accurate information about network links.

In MPLS TE, the link-state database (LSDB) maintained by these routing protocols provides an up-to-date, detailed view of the network topology. This database contains information about each router's neighbors, links, link costs, and other relevant data that helps in determining the best paths for LSPs. The link-state protocol allows for the calculation of these paths using algorithms such as SPF (Shortest Path First), which are critical for the establishment of MPLS TE tunnels.

Why a Link-State Routing Protocol is Necessary

The reason a link-state routing protocol is necessary for MPLS TE tunnels is that it allows tunnel endpoints to evaluate the entire network topology and determine the best possible path for traffic. MPLS TE tunnels are not only about selecting the shortest path, but also considering bandwidth constraints, load balancing, and network congestion. The link-state database, which is continually updated, provides tunnel endpoints with all the information required to make intelligent path selections for the LSPs.

Each router in the network uses SPF calculations to determine the best path based on various metrics like link bandwidth and administrative distance. For MPLS TE to effectively manage traffic across the network, these SPF calculations need to be based on a complete and accurate representation of the network topology, which is provided by the link-state routing protocol.

Analysis of the Options

Option A: "The link-state database provides segmentation by area, which enhances the path-selection process."

This option is incorrect because segmentation by area is a characteristic of OSPF areas, and while area segmentation can help in scaling OSPF, it does not directly influence MPLS TE path selection. The path-selection process in MPLS TE is primarily determined by the availability of bandwidth and the topology database, not by segmentation.

Option B: "The link-state database provides a data repository from which tunnel endpoints can dynamically select a source ID."

This statement is misleading. The selection of a source ID for MPLS TE tunnels typically involves the configuration of tunnel endpoints (ingress and egress routers) and not dynamic selection from the link-state database. The link-state database provides topological information, but it is not specifically used to select a source ID for the tunnel.

Option C: "Link-state routing protocols use SPF calculations that the tunnel endpoints leverage to establish the tunnel."

While it is true that SPF calculations are involved, this statement is incomplete and somewhat misleading. SPF calculations are used to determine the best path, but the key point is that tunnel endpoints leverage the link-state database to evaluate the entire topology. This includes considering link bandwidth, congestion, and other metrics beyond just SPF, making option D a more accurate and complete description.

Option D: "The tunnel endpoints use the link-state database to evaluate the entire network topology and determine the best path."

This statement is the most accurate and complete. It correctly describes the role of the link-state database in MPLS TE. By using the full topology information, including link characteristics such as bandwidth and current utilization, MPLS TE can calculate optimal paths for traffic flows, providing better load balancing, efficient use of network resources, and avoidance of network congestion.

How Link-State Protocols Enable Efficient Traffic Engineering

Link-state routing protocols like OSPF and IS-IS provide a comprehensive view of the network topology. This enables routers to calculate the shortest path from one node to another, but also to consider traffic engineering parameters such as available bandwidth, delay, and link utilization. In MPLS TE, this is critical because it allows traffic to be directed along paths that are not only optimal in terms of shortest distance but also take into account the actual state of the network links.

MPLS TE uses constraint-based routing to set up Label Switched Paths (LSPs). The constraints can include bandwidth requirements, maximum delay, and other QoS (Quality of Service) parameters. The link-state database provides the necessary information to meet these constraints and create LSPs that optimize network performance. Without the link-state protocol, the network would not have the complete, real-time topology information necessary to make these informed decisions.

Additionally, the link-state database in MPLS TE ensures that the network can adapt dynamically to changes in topology, such as link failures or congestion. As the network topology changes, the link-state protocol recalculates the SPF and updates the database, allowing for the rapid re-establishment of tunnels and rerouting of traffic to avoid congested or failed paths.

Question No 4:

Refer to the exhibit. BGPsec is implemented on R1, R2, R3, and R4. BGP peering is established between neighboring autonomous systems. Based on this configuration, which of the following statements about the implementation of BGPsec is true?

A. BGP updates from iBGP peers are appended with a community of local-as.
B. BGP updates from all BGP peers are appended with a community of no-export.
C. BGP updates from eBGP peers are appended with an additional AS path value that is statically set by the domain administrator.
D. BGP updates from eBGP peers are appended with a BGPsec attribute sequence that includes a public key hash and digital signature.

Answer:

The correct answer is D. BGP updates from eBGP peers are appended with a BGPsec attribute sequence that includes a public key hash and digital signature.

Explanation:

BGPsec (Border Gateway Protocol Security) is an extension to the standard BGP (Border Gateway Protocol) that introduces cryptographic verification of BGP updates. BGPsec aims to provide a way to ensure the authenticity and integrity of BGP announcements, specifically to prevent attacks such as route hijacking and to verify that the AS path for a given prefix is legitimate. This is achieved by using digital signatures and public key cryptography to secure BGP updates.

Let’s analyze each option in detail to understand why D is the correct answer.

Option A: "BGP updates from iBGP peers are appended with a community of local-as."

This option is incorrect. While BGP updates can include various attributes, including communities, the implementation of BGPsec does not automatically append a "local-as" community to iBGP updates. Communities are typically used in BGP for tagging and controlling routing behavior, but they are not directly tied to the security attributes introduced by BGPsec.

The BGPsec protocol, instead, focuses on securing the integrity of the AS path and ensuring the validity of the BGP route announcements through digital signatures, not on community attributes for local-AS management.

Thus, this option does not reflect the behavior described in the question.

Option B: "BGP updates from all BGP peers are appended with a community of no-export."

This statement is incorrect as well. The "no-export" community in BGP is used to prevent the advertisement of routes to external peers. However, it is not related to the BGPsec protocol or its cryptographic enhancements. BGPsec does not automatically append the "no-export" community to all BGP updates from peers.

BGPsec is concerned with verifying the authenticity of the AS path through digital signatures and public key infrastructure (PKI), rather than using the "no-export" community for controlling route advertisement behavior.

Thus, the use of the "no-export" community does not apply to BGPsec implementations, making this option inaccurate.

Option C: "BGP updates from eBGP peers are appended with an additional AS path value that is statically set by the domain administrator."

This statement is incorrect. While BGP updates from eBGP peers indeed carry an AS path, this option confuses the operation of BGPsec. In BGPsec, the AS path is not statically set by the domain administrator. Instead, the AS path is cryptographically signed to verify its legitimacy.

The BGPsec extension appends security attributes to the BGP update, but these attributes are not related to statically setting the AS path. The AS path is dynamically built as the BGP route is propagated through different ASes, and its validity is verified by the BGPsec signatures.

Thus, this option does not accurately describe BGPsec’s functionality, as BGPsec does not involve statically setting the AS path.

Option D: "BGP updates from eBGP peers are appended with a BGPsec attribute sequence that includes a public key hash and digital signature."

This statement is correct. The key feature of BGPsec is the addition of cryptographic signatures to BGP updates. Specifically, BGPsec adds an attribute known as the "BGPsec Path Attribute" to the BGP update. This attribute contains a sequence of cryptographic data that includes:

A public key hash: This allows peers to verify the identity of the AS that originated the route announcement.
A digital signature: This ensures that the BGP update is authentic and has not been tampered with. The signature is generated using the private key of the AS that is advertising the route.

The use of a public key hash and a digital signature is fundamental to the security enhancements provided by BGPsec. These cryptographic measures allow routers to verify the legitimacy of a BGP update and ensure that it follows a valid and secure AS path. This method prevents malicious actors from injecting fraudulent routes into the network and helps secure the global BGP routing table.

Question No 5:

An engineer is in the process of configuring MPLS Traffic Engineering (MPLS-TE) tunnels within the service provider core network.
The goal is to optimize the traffic flow and ensure bandwidth guarantees across multiple routers.
The engineer must decide how to establish the tunnel paths across the MPLS core.

Which two characteristics accurately describe the methods available for defining the tunnel paths in MPLS-TE configuration?(Choose two.)

A. The dynamic path option is supported only when using IS-IS as the IGP.
B. Tunnel paths can either be dynamically calculated or explicitly defined by the administrator.
C. A tunnel configured with zero bandwidth is not considered a valid or functional option.
D. The bandwidth command on a tunnel interface causes a strict (hard) reservation of bandwidth resources on each link.
E. By default, tunnel interfaces inherit IGP link metrics unless these metrics are manually overridden.

Correct Answers:

B. Tunnel paths can either be dynamically calculated or explicitly defined by the administrator.
E. By default, tunnel interfaces inherit IGP link metrics unless these metrics are manually overridden.

Explanation:

In MPLS Traffic Engineering (MPLS-TE), there are two primary methods for defining the path of a tunnel across the core:

Dynamic Path Computation:
In this method, the router automatically computes the best path using Constraint-Based Shortest Path First (CSPF) calculations. CSPF factors in network constraints such as bandwidth, affinities, and link availability, and selects the optimal path dynamically. Dynamic path calculation works with both OSPF and IS-IS as the Interior Gateway Protocols (IGPs) — not just IS-IS, making Option A incorrect.
Explicit Path Definition:
The engineer can also manually configure an explicit path by listing specific hops (router addresses) the tunnel must follow. This provides deterministic routing through the network but requires manual maintenance if network topology changes.

By default, when a tunnel is configured, its metric is inherited from the underlying IGP link. If needed, the administrator can manually override the tunnel metric to influence path selection — validating Option E.

Regarding other choices:

Zero bandwidth tunnels are valid. They are often used when bandwidth reservations are not necessary but TE functionality (such as fast reroute) is still desired. Therefore, Option C is incorrect.
The bandwidth statement does not create a hard, inflexible reservation immediately. It simply signals the bandwidth requirement, and RSVP (Resource Reservation Protocol) tries to honor it dynamically based on available resources, making Option D incorrect.

In summary, dynamic and explicit path options are both valid, and IGP metric inheritance is the default behavior unless otherwise configured.