Cisco 300-515 Exam Dumps & Practice Test Questions

Question 1:

Which tool is used to verify and validate a Label Switched Path (LSP) in an MPLS network?

A. uRPF
B. MPLS LSP ping
C. logging
D. RSVP

Correct Answer: B

Explanation:

In an MPLS (Multiprotocol Label Switching) environment, it is crucial to ensure that Label Switched Paths (LSPs) are functioning correctly and forwarding traffic as intended. The specialized utility designed for this purpose is the MPLS LSP ping. This tool operates similarly to the traditional ping utility but is enhanced to work within MPLS networks. It sends test packets along the specific LSP, allowing network administrators to confirm the continuity and integrity of the path. This ensures that the labels assigned in the MPLS network properly guide the packets through the network nodes to their destination.

The MPLS LSP ping can help detect issues such as label misconfigurations, unreachable nodes along the path, or incorrect label assignments. It is a vital troubleshooting and validation tool for network engineers managing MPLS infrastructures.

Other options do not serve this specific purpose:

• uRPF (Unicast Reverse Path Forwarding) is a security feature that helps prevent IP spoofing by verifying that incoming packets have valid source addresses according to routing tables. It is unrelated to validating MPLS LSPs.

• Logging is a generic monitoring method to record events and errors on network devices but does not actively test or verify MPLS paths.

• RSVP (Resource Reservation Protocol) is a signaling protocol used to establish and reserve resources for LSPs, helping create and maintain paths rather than validate them after creation.

Thus, MPLS LSP ping is the dedicated tool for validating MPLS LSPs, making option B the correct choice.

Question 2:

What is the main purpose of implementing Virtual Routing and Forwarding (VRF) on a router?

A. To enable the router to maintain multiple independent routing tables, allowing it to manage overlapping IP addresses.
B. To allow the router to run both BGP and a distance-vector routing protocol simultaneously and serve as a VPN endpoint.
C. To locally configure VLANs on the router for network segregation.
D. To speed up switching by using labels to identify input and output interfaces on neighboring routers.

Correct Answer: A

Explanation:

The core function of Virtual Routing and Forwarding (VRF) on a router is to provide multiple, isolated routing tables on the same physical device. This capability allows the router to support overlapping IP address spaces by segregating network traffic logically across different VRFs. Each VRF acts like a separate virtual router, with its own routing table and forwarding decisions. This logical partitioning is particularly valuable in environments such as service provider networks, where multiple customers might share the same physical infrastructure but require isolated networks with potentially overlapping IP subnets.

By maintaining distinct routing tables, VRF ensures that packets belonging to different virtual networks do not mix, providing a layer of security and traffic separation while optimizing hardware use.

The other options misrepresent the primary role of VRF:

• Option B refers to running multiple routing protocols simultaneously (e.g., BGP and a distance-vector protocol). While a router can do this, it is unrelated to VRF's main feature of multiple routing tables. VRF enables isolation, not protocol multiplexing.

• Option C describes VLAN configuration, which is a Layer 2 segmentation method and is unrelated to VRF’s Layer 3 routing separation.

• Option D describes MPLS functionality where labels accelerate packet forwarding, which is separate from VRF’s logical routing table isolation.

Therefore, option A is the correct answer as VRF’s primary role is to enable multiple virtual routing instances that can handle overlapping IP spaces while logically separating networks on the same router.

Question 3:

Which two statements correctly explain the main differences between MPLS Layer 2 VPNs and Layer 3 VPNs? (Select two.)

A. Layer 2 VPNs use IPsec tunneling, whereas Layer 3 VPNs use L2TPv3 tunneling.
B. Layer 2 VPNs rely on AToM technology, while Layer 3 VPNs use MPLS combined with BGP.
C. Layer 2 VPNs utilize BGP for routing, but Layer 3 VPNs implement VPLS.
D. Layer 2 VPNs use L2TPv3 tunneling, and Layer 3 VPNs employ GRE tunnels.
E. Layer 2 VPNs make use of IPsec tunneling, whereas Layer 3 VPNs utilize pseudowires for tunneling.

Correct Answers: B, E

Explanation:

MPLS VPN technology enables private networking over shared infrastructure, but Layer 2 VPNs (L2VPNs) and Layer 3 VPNs (L3VPNs) differ significantly in their operation, protocols, and encapsulation methods.

Option B highlights a key difference: Layer 2 VPNs generally use AToM (Any Transport over MPLS) to transport Layer 2 frames, such as Ethernet, ATM, or Frame Relay, over an MPLS backbone. This method provides point-to-point connectivity at the data link layer. Conversely, Layer 3 VPNs use MPLS combined with BGP (Border Gateway Protocol) to route IP packets between customer sites. BGP manages the routing tables for each customer’s VPN, facilitating IP-level routing and scalability across the provider network.

Option E also correctly distinguishes the two types by tunneling approach. Layer 2 VPNs often employ IPsec tunneling to secure Layer 2 traffic, especially when it traverses untrusted or public networks, maintaining Layer 2 connectivity with encryption. Layer 3 VPNs, however, utilize pseudowires, virtual point-to-point links over MPLS that forward Layer 3 packets transparently while preserving routing functions without relying on IPsec.

The other options contain inaccuracies:

• Option A misattributes IPsec to Layer 2 VPNs and L2TPv3 to Layer 3 VPNs, which is reversed or incorrect.

• Option C incorrectly states Layer 2 VPNs use BGP; they typically use VPLS or AToM for Layer 2 connectivity, while Layer 3 VPNs employ BGP.

• Option D incorrectly associates GRE tunneling with Layer 3 MPLS VPNs, which primarily use MPLS/BGP, not GRE.

In summary, B and E correctly identify the fundamental differences in technology and tunneling mechanisms between MPLS Layer 2 and Layer 3 VPNs.

Question 4:

Given the exhibit, a network engineer is tasked with configuring four PE routers to enable seamless communication among their connected CE devices. Upon beginning, connectivity issues arise. 

Which two steps should the engineer take first to properly start the configuration? (Select two.)

A. Configure PE3 to export route-targets 100:1 and 200:2.
B. Configure PE3 to import route-targets 100:1 and 200:2.
C. Configure PE4 to import route-targets 101:1 and 202:2.
D. Configure PE2 to export route-targets 300:3 and 400:4.
E. Configure PE1 to import route-targets 300:3 and 400:4.

Correct Answers: B, C

Explanation:

In MPLS VPN architectures, route-targets are critical extended BGP community attributes used to control the import and export of VPN routes between Provider Edge (PE) routers. Proper configuration of these route-targets is essential for the exchange of routing information that enables customer devices (CEs) to communicate across the service provider’s network.

The question describes a scenario where the engineer faces connectivity problems after starting PE configuration. To resolve this, focus should be on ensuring that the PE devices import the correct route-targets corresponding to the VPNs they need to communicate with.

• Option B is correct because configuring PE3 to import route-targets 100:1 and 200:2 enables it to receive routing updates from the VPNs associated with those route-targets. This import action ensures PE3 knows about the routes from its peers and can forward traffic accordingly.

• Option C is also correct. PE4 must be configured to import route-targets 101:1 and 202:2 to gain knowledge of routes from other VPN sites, facilitating end-to-end communication.

The other options are less critical at this initial stage:

• Option A involves exporting route-targets from PE3, which is important but secondary to ensuring the correct import configuration to fix connectivity issues.

• Option D deals with PE2 exporting route-targets, but until imports are correct, this export is not the immediate cause of the connectivity problem.

• Option E references PE1’s import settings, which may be correct eventually but does not directly address the current connectivity issue involving PE3 and PE4.

In summary, the priority for resolving such connectivity issues is ensuring that PE routers are importing the correct route-targets, making B and C the appropriate first steps.

Question 5:

Based on the given configuration and assuming both devices are functioning properly, which two conclusions can be drawn? (Select two.)

A. CE1 is required to use OSPF to form a neighbor relationship with PE1.
B. PE1 assigns the route-target 222:2 to routes learned from CE1 and shares them with its VPNv4 peers.
C. PE1 tags routes it receives from CE1 with route-target 111:1 and advertises them to its VPNv4 peers.
D. The PE and CE devices exchange routes using OSPF.
E. CE1 supports Customer Service Configuration (CSC).

Correct Answers: C, D

Explanation:

In this scenario, the two devices involved, PE1 (Provider Edge) and CE1 (Customer Edge), are part of an MPLS VPN setup where PE1 connects with other VPNv4 peers to exchange routes, and CE1 exchanges routing information with PE1.

Option C is correct because in MPLS VPN architectures, PE routers tag routes learned from CE devices with specific route-targets. These route-targets are used to control the import and export of routes between VPN sites. The tag 111:1 mentioned here represents the route-target applied by PE1, which it uses to share these routes with its VPNv4 peers. This is a common mechanism for route distribution in MPLS VPNs.

Option D is also correct because it identifies the routing protocol used between PE1 and CE1. OSPF is a popular interior gateway protocol (IGP) used for exchanging routes in many provider-customer setups. It suggests that the PE-CE route exchange is conducted using OSPF.

Option A is incorrect. While OSPF is commonly used for PE-CE routing, the configuration does not mandate that CE1 must use OSPF. Other routing protocols like BGP or EIGRP could also be configured depending on the deployment.

Option B is incorrect because it mentions a different route-target (222:2), which is not consistent with the shown configuration. The route-target must match the one configured to identify the VPN correctly.

Option E is not supported by the provided configuration details. There is no indication that CE1 supports CSC, and it is irrelevant to this MPLS VPN setup.

In summary, the correct conclusions are that PE1 tags routes from CE1 with 111:1 and advertises them to VPNv4 peers, and that OSPF is used for route exchange between PE and CE.

Question 6:

Which two types of frames can be configured on an Ethernet flow point? (Select two.)

A. Frames belonging to a specific VLAN
B. Frames with varying Type of Service (ToS) values
C. Frames with identical Type of Service (ToS) values
D. Frames with different Class of Service (CoS) values
E. Untagged frames (no VLAN tags)

Correct Answers: A, C

Explanation:

Ethernet flow points are important for managing and controlling traffic flows on a network, particularly concerning Quality of Service (QoS) and VLAN handling. They enable administrators to apply policies or prioritize traffic based on certain frame characteristics.

Option A is correct because an Ethernet flow point can be configured to handle traffic tied to a specific VLAN. VLAN tagging segregates traffic logically within the same physical infrastructure, and managing frames of a specific VLAN helps ensure the proper routing and application of QoS policies for that segment.

Option C is also correct because Ethernet flow points can manage traffic flows where frames have identical Type of Service (ToS) values. The ToS field in the IP header (or DSCP in more modern terms) indicates packet priority and helps in traffic classification and prioritization across the network.

Option B is incorrect. Although ToS values can be used to differentiate traffic priorities, configuring a flow point to handle multiple different ToS values simultaneously is not typical. Instead, network-wide QoS policies or classifiers are used to handle varying ToS values rather than configuring the flow point itself.

Option D is incorrect because Class of Service (CoS) relates to layer 2 frame priority, often used within VLAN tags, but configuring flow points with multiple differing CoS values would generally require more advanced QoS configurations and isn’t standard at a basic flow point level.

Option E is incorrect because untagged frames (frames without VLAN tags) are normal Ethernet frames but flow points are usually intended to manage tagged traffic flows where VLAN or QoS information is present.

In summary, Ethernet flow points are configured to control traffic either associated with a specific VLAN or with uniform ToS values, enabling efficient traffic segregation and QoS enforcement.

Question 7:

Within an Ethernet Virtual Circuit setup, what limitation applies to bridge domains when Spanning Tree Protocol (STP) is enabled?

A. The STP mode must be Rapid Spanning Tree Protocol (RSTP) or Per VLAN Spanning Tree Plus (PVST+)
B. Each bridge domain must be assigned to a distinct VLAN
C. The STP mode must be Multiple Spanning Tree Protocol (MSTP)
D. Bridge domains are required to belong to different MST instances

Correct Answer: C

Explanation:

In environments utilizing Ethernet Virtual Circuits, the Spanning Tree Protocol (STP) ensures loop-free Layer 2 topologies. When STP operates in these networks that involve multiple bridge domains, the specific STP mode required is Multiple Spanning Tree Protocol (MSTP).

MSTP is designed to enhance scalability and efficiency by allowing multiple VLANs to be mapped into a single spanning tree instance. This reduces the overhead compared to running a separate spanning tree for every VLAN, which is the case with protocols like PVST+. Since bridge domains are typically aligned with VLANs, MSTP enables grouping several VLANs and their bridge domains under fewer spanning tree instances. This capability makes MSTP especially suited for complex Ethernet Virtual Circuit environments where multiple bridge domains coexist.

Option A is incorrect because RSTP and PVST+ do not efficiently handle multiple VLANs and bridge domains in such environments. RSTP is faster than traditional STP but does not offer the VLAN-instance mapping capabilities of MSTP, and PVST+ runs one spanning tree per VLAN, which is less scalable.

Option B mentions mapping bridge domains to different VLANs, which is common practice but not an STP-related limitation or requirement under STP operation.

Option D suggests that bridge domains must belong to different MST instances. However, MSTP allows multiple bridge domains to exist within the same MST instance, so this is not a mandatory restriction.

In summary, MSTP is the required STP mode in Ethernet Virtual Circuit setups with multiple bridge domains, making C the correct answer.

Question 8:

In an MPLS Point-to-Multipoint (P2MP) Traffic Engineering (TE) deployment, which router role can function both as an intermediate (midpoint) and as a final (tailend) router?

A. Headend router
B. Source router
C. Transit router
D. Bud router

Correct Answer: D

Explanation:

In an MPLS Point-to-Multipoint (P2MP) Traffic Engineering network, routers have specific roles that determine how traffic flows from the source to multiple destinations. The bud router is unique in that it can act as both an intermediate (midpoint) router and a final (tailend) router in the P2MP TE topology.

The bud router is named for its function resembling a “branching point” (or “bud”) where traffic from the headend or source router splits to multiple downstream paths. It receives traffic from the headend and forwards it along to other routers downstream. Additionally, the bud router can be the endpoint for some traffic streams, acting as the destination for others. This dual role distinguishes it from other router types in the MPLS P2MP environment.

Let's review the other options:

• The headend router is the starting point of the P2MP traffic, responsible for originating and sending traffic into the network. It does not serve as a midpoint or tailend router.

• The source router is effectively the same as the headend—it initiates traffic flow but does not serve mid-network or destination roles.

• Transit routers simply forward traffic along the established path and do not serve as endpoints or branching points; they are purely forwarding devices without destination responsibilities.

Because the bud router both relays traffic and can terminate some branches, it is the only router role capable of functioning as both a midpoint and tailend router in an MPLS P2MP TE network, confirming D as the correct choice.

Question 9:

While troubleshooting an EVPN traffic flow problem, which type of traffic should be permitted within an EVPN Tree Service to resolve the issue?

A. Known unicast traffic sent from one leaf node to another leaf node
B. Unknown unicast traffic sent from one leaf node to another leaf node
C. Multicast traffic sent from one leaf node to another leaf node
D. Known unicast traffic sent from one root node to another root node

Correct Answer: B

Explanation:

In an EVPN (Ethernet Virtual Private Network) architecture, the way different types of traffic are handled between nodes—especially leaf nodes—is critical for proper network operation. EVPN separates traffic types into known unicast, unknown unicast, multicast, and broadcast. Understanding these distinctions helps pinpoint where traffic flow issues might arise.

Known unicast traffic refers to packets addressed to a destination MAC address that the network already knows and has learned through the control plane. Typically, this traffic flows smoothly once the MAC addresses are advertised and installed in the forwarding tables. However, problems with known unicast traffic are less common unless MAC learning is flawed.

Unknown unicast traffic consists of packets sent to destinations whose MAC addresses are not yet known by the network. EVPN handles this type of traffic by flooding it across a multicast distribution tree. This flooding ensures the packet reaches all potential receivers, allowing devices to learn the MAC addresses dynamically. If multicast forwarding or flooding of unknown unicast traffic is blocked or misconfigured, traffic flow between leaves can break, causing communication failures.

Multicast traffic in EVPN is designed for efficient delivery to multiple receivers, but multicast issues generally affect group communication rather than direct unicast flows between leaf nodes. Therefore, multicast traffic is not the primary concern when dealing with unknown unicast forwarding problems.

Known unicast from root to root usually involves communication between central nodes managing the network, and is less likely to be the cause of leaf-to-leaf traffic issues.

The most common root cause for EVPN leaf traffic flow problems is improper handling of unknown unicast traffic. Enabling and properly configuring the multicast distribution tree to allow unknown unicast traffic ensures packets are flooded correctly, enabling MAC address learning and restoring connectivity. Hence, option B is the correct answer.

Question 10:

Which command should an engineer run on a Cisco IOS XE device to view the Label Forwarding Information Base (LFIB) when diagnosing an MPLS LDP problem?

A. show mpls forwarding-table
B. show mpls ldp neighbors
C. show mpls ldp labels
D. show mpls ldp bindings

Correct Answer: A

Explanation:

In an MPLS (Multiprotocol Label Switching) network, the Label Forwarding Information Base (LFIB) is essential for packet forwarding. The LFIB contains information that maps incoming MPLS labels to outgoing labels and corresponding outgoing interfaces. This allows the device to forward labeled packets correctly through the MPLS network based on label switching rather than traditional IP routing.

When troubleshooting MPLS Label Distribution Protocol (LDP) issues, the engineer needs to verify how labels are being forwarded by the device. The command show mpls forwarding-table displays the contents of the LFIB, listing all label-switched paths with their associated incoming and outgoing labels and interfaces. This output is crucial for understanding the actual forwarding behavior and identifying misconfigurations or missing label bindings.

Option B (show mpls ldp neighbors) provides information about LDP peer adjacencies but does not show forwarding details. It helps verify neighbor relationships but not the label forwarding state.

Option C (show mpls ldp labels) shows the labels assigned by LDP for various Forwarding Equivalence Classes (FECs) but does not include the forwarding mappings that the LFIB provides.

Option D (show mpls ldp bindings) lists label bindings learned or advertised by LDP but again does not display the actual LFIB entries used for forwarding decisions.

In summary, the LFIB represents the MPLS forwarding plane’s actual forwarding decisions. To inspect it, the correct command is show mpls forwarding-table, which corresponds to option A. This command helps the engineer diagnose label forwarding problems by revealing how the device processes MPLS-labeled packets internally.