Cisco 300-515 Exam Dumps & Practice Test Questions
Question No 1:
When setting up EVPN using native configuration on a router that supports both EVPN and L2VPN modes,
Which parameter must be identical in both configurations to guarantee proper alignment between the control and data planes?
A. Interface
B. Address Family
C. Bridge Domain
D. Ethernet VPN Instance (EVI)
Correct Answer: D. Ethernet VPN Instance (EVI)
Explanation:
Ethernet VPN (EVPN) is a protocol designed to deliver scalable Layer 2 and Layer 3 VPN services over an IP or MPLS core using BGP for signaling. On platforms where EVPN is configured in conjunction with L2VPN settings, it’s essential that specific identifiers are synchronized to ensure cohesive service delivery.
One such critical identifier is the Ethernet VPN Instance (EVI). The EVI acts as the logical tag that uniquely identifies each EVPN service instance. It links the EVPN BGP control plane—which manages MAC advertisement and label signaling—with the local forwarding infrastructure defined in L2VPN, such as bridge domains and access circuits.
For seamless operation, the same EVI value must be defined in both EVPN and L2VPN configuration contexts. If there's a mismatch, the control and data planes will be disconnected, leading to MAC learning issues, failed route propagation, or even a breakdown of the VPN service.
While Interface, Address Family, and Bridge Domain are relevant to configuring EVPN and L2VPN individually, they do not serve as the vital binding element between the two. Only the EVI ensures proper mapping between BGP announcements and the Layer 2 forwarding path. Therefore, maintaining consistency in EVI across both configurations is essential for EVPN to function correctly.
Question No 2:
While configuring Any Transport over MPLS (AToM) on a Cisco IOS XE router, an engineer encounters an error after entering the xconnect command under an interface.
This issue usually points to a missing prerequisite step. Which configuration must be applied on the interface before using the xconnect command?
A. encapsulation mpls
B. encapsulation l2tpv3
C. protocol l2tpv3
D. protocol none
Correct Answer: A. encapsulation mpls
Explanation:
AToM (Any Transport over MPLS) is a Cisco-specific solution that facilitates Layer 2 VPN connectivity over an MPLS infrastructure. It encapsulates Layer 2 frames in MPLS and transports them between edge routers. When implementing this feature, the interface designated for Layer 2 transport must support the required encapsulation type.
The encapsulation mpls command is essential because it enables the interface to handle MPLS-tagged frames—without it, the router won't recognize or forward Layer 2 VPN traffic through the MPLS core. The xconnect command binds this MPLS-capable interface to a remote PE (Provider Edge) router, allowing Layer 2 frames to be tunneled point-to-point.
If encapsulation mpls is not applied, the router cannot process the AToM configuration properly, and issuing the xconnect command will result in an error. Alternative encapsulation types like encapsulation l2tpv3 or protocol l2tpv3 are used in a different transport model—L2TPv3—and are not compatible with AToM, which relies strictly on MPLS encapsulation. Similarly, protocol none provides no encapsulation and is unsuitable for any transport scenario requiring tunneling.
Thus, configuring encapsulation mpls is a mandatory step when preparing the interface for AToM tunneling.
Question No 3:
A network engineer is working to resolve an issue with an EoMPLS (Ethernet over MPLS) circuit on a Cisco IOS XR router. The goal is to remove a VLAN from the distribution layer.
Which of the following configurations will accomplish this?
A.
interface GigabitEthernet 0/10.l2transport
encapsulation dot1q 10
rewrite ingress tag pop 1 symmetric
l2vpn xconnect group 103588 p2p 103588
interface GigabitEthernet 0/10.10
neighbor ipv4 10.10.10.2 pw-id 103588
B.
interface GigabitEthernet 0/10.10
encapsulation dot1q 10
rewrite ingress tag pop 1 symmetric
l2vpn xconnect group 103588 p2p 103588
interface GigabitEthernet 0/10.10
neighbor ipv4 10.10.10.2 pw-id 103588
C.
interface GigabitEthernet 0/10.10 l2transport
encapsulation dot1q 10
l2vpn xconnect group 103588 p2p 103588
interface GigabitEthernet 2/10.10
neighbor ipv4 10.10.10.2 pw-id 103588
D.
interface GigabitEthernet 0/10.10 l2transport
encapsulation dot1q 10
rewrite ingress tag translate 1-to-1 dot1ad 10 symmetric
l2vpn xconnect group 103588 p2p 103588
interface GigabitEthernet 0/10.10
neighbor ipv4 10.10.10.2 pw-id 103588
Correct Answer:
A. interface GigabitEthernet 0/10.l2transport
encapsulation dot1q 10
rewrite ingress tag pop 1 symmetric
l2vpn xconnect group 103588 p2p 103588
interface GigabitEthernet 0/10.10
neighbor ipv4 10.10.10.2 pw-id 103588
Explanation:
EoMPLS enables the transport of Ethernet frames over an MPLS network, extending Layer 2 connectivity between distant locations. The task involves removing a VLAN as traffic enters the router. The command rewrite ingress tag pop 1 symmetric removes the VLAN tag from the incoming frame, ensuring it is not carried over the MPLS core. This process is essential for transporting traffic across an MPLS backbone without retaining VLAN identifiers.
Option A is correct because it uses the l2transport mode required for EoMPLS and includes the necessary encapsulation and tag rewrite commands. The symmetric keyword ensures proper bidirectional behavior. The l2vpn xconnect section then sets up the point-to-point connection using a specific pseudowire ID.
Option B is incorrect as it lacks the l2transport keyword.
Option C does not include the tag pop operation, failing to remove the VLAN as required.
Option D incorrectly applies a translate 1-to-1 dot1ad tag rewrite, which is meant for 802.1ad (QinQ) and not standard dot1q VLAN removal.
Question No 4:
While deploying Layer 3 MPLS VPN services on Cisco IOS or IOS XE Provider Edge (PE) routers, a network engineer needs to configure routing protocols for PE-to-CE connectivity.
Which routing protocol specifically mandates a separate routing process for each VRF instance configured on the PE router?
A. RIPv2
B. OSPF
C. BGP
D. EIGRP
Correct Answer: B. OSPF
Explanation:
In a Layer 3 MPLS VPN architecture, PE routers rely on Virtual Routing and Forwarding (VRF) instances to isolate each customer’s routing information. These VRFs act as virtual routers, each maintaining an independent routing table. Routing protocols are used between the PE and CE (Customer Edge) routers to exchange route information for each customer network. The integration of these protocols into VRFs varies in complexity depending on the protocol.
OSPF (Open Shortest Path First) is unique among the commonly used routing protocols in this context because it does not natively support multi-VRF operation under a single OSPF process. Instead, it requires that each VRF be configured with a distinct OSPF process. This design choice ensures that OSPF maintains complete isolation between customer routing domains. Consequently, for every VRF that leverages OSPF as the PE-to-CE routing protocol, a separate OSPF process ID must be defined and managed.
On the other hand, protocols like RIPv2, BGP, and EIGRP are more flexible. RIPv2 can be configured within multiple VRFs using a single process and proper interface bindings. BGP, widely used in MPLS VPNs for exchanging VPNv4 routes between PEs, is inherently VRF-aware. It uses address families and route distinguishers to manage customer route separation and can handle multiple VRFs using a single BGP process. EIGRP, although proprietary to Cisco, also supports VRF-aware functionality and allows a single EIGRP instance to service multiple VRFs by associating each interface with the corresponding VRF context.
In summary, while most protocols offer multi-VRF support within a single process, OSPF stands out as requiring a unique process per VRF. This makes configuration more granular and potentially more complex to manage, but it also ensures strict isolation between customers’ routing information. Therefore, OSPF is the correct answer.
Question No 5:
In order to correctly implement Carrier-Supporting Carrier (CSC) functionality within an MPLS-based network, which technical requirement must be met to ensure the CSC-PE and CSC-CE devices interact appropriately?
A. The CSC-PE and CSC-CE must each be able to ping a global interface.
B. Both CSC-PE and CSC-CE must have full support for IPv6.
C. The CSC-PE and CSC-CE must exchange MPLS labels via BGP.
D. The CSC-CE must be capable of running OSPFv3.
Correct Answer: C. The CSC-PE and CSC-CE must exchange MPLS labels via BGP
Explanation:
Carrier-Supporting Carrier (CSC) is a specialized deployment model within MPLS architectures where a provider’s provider is responsible for routing and label switching for another service provider (the customer). This design enhances scalability and simplifies the management of complex, hierarchical MPLS environments, typically found in inter-carrier or multi-tiered provider networks.
For CSC to function correctly, the exchange of MPLS labels between the Carrier Supporting Carrier’s Provider Edge (CSC-PE) and the Customer Carrier’s Edge (CSC-CE) is mandatory. This label exchange is achieved using Multiprotocol BGP (MP-BGP), specifically the Labeled Unicast (LU) address family. Through this mechanism, labels are distributed along with routing information, allowing the CSC-PE to establish end-to-end MPLS paths for the VPN or Internet routes advertised by the CSC-CE.
This approach ensures traffic is properly label-switched across the core of the backbone carrier without requiring visibility into the customer carrier’s entire routing table. It provides both operational abstraction and administrative separation, which are essential in service provider environments.
Other answer options, while technically related to broader networking concepts, do not fulfill the core requirement of label exchange for CSC. For instance:
Option A, the ability to ping, only confirms basic IP reachability and does not pertain to MPLS label distribution.
Option B, support for IPv6, is unrelated to CSC’s core function, which operates over MPLS irrespective of IP version.
Option D, OSPFv3, is a routing protocol used internally but not necessary for CSC label dissemination.
Thus, for CSC to operate effectively, the CSC-PE and CSC-CE must support BGP-based MPLS label exchange, making Option C the correct and essential requirement.
Question No 6:
In a Layer 3 MPLS VPN environment, what is the most likely cause of certain VPNv4 routes failing to propagate between Provider Edge (PE) routers?
A. Route Distinguisher (RD) mismatch between PE routers
B. Misconfiguration in Route Target (RT) export and import
C. Inconsistent VRF names on PE routers
D. Misconfiguration in RD export and import
Correct Answer: B. Misconfiguration in Route Target (RT) export and import
Explanation:
In Layer 3 MPLS VPN deployments, the interaction between VPNv4 routes across Provider Edge (PE) routers is central to routing and traffic forwarding within the MPLS backbone. A VPNv4 route is identified by two key elements: the Route Distinguisher (RD) and the Route Target (RT). These attributes play a crucial role in route separation, identification, and propagation.
Route Distinguisher (RD):
The RD is used to maintain route uniqueness across different VPNs by appending a unique identifier to the IP address, effectively ensuring that routes from different VPNs, even if they have overlapping IP address spaces, are treated as distinct.Route Target (RT):
The RT, on the other hand, dictates which VPNs (Virtual Routing and Forwarding instances, or VRFs) should share routes with one another across PE routers. The RT is the key element that determines whether a VPNv4 route can be imported into the correct VRF on a PE router.
In the case of VPNv4 routes failing to propagate, the most likely cause is a misconfiguration in Route Target (RT) export and import. If a PE router exports a route with a specific RT that is not being imported on the receiving PE router, the route will not be seen by the receiving router. This RT misalignment prevents the propagation of routes between PE routers and can disrupt connectivity within the VPN.
Now, let’s explore why the other options are less likely to be the root cause:
Option A (RD mismatch):
The RD’s purpose is to ensure unique identification of routes; it does not influence route propagation. As such, a mismatch in RD values between PE routers would not cause failure in route propagation. Even with different RDs, the routes would still propagate, assuming the RTs are correctly configured.Option C (Inconsistent VRF names):
While inconsistent VRF names can lead to confusion and potential misconfigurations, they do not directly impact route propagation. As long as the RTs are configured correctly and match across the PE routers, routes should propagate regardless of VRF name inconsistencies. The names themselves are used for identification but do not affect the actual route exchange mechanism.Option D (Misconfiguration in RD export/import):
There is no concept of RD export or import in the MPLS VPN configuration. The RD is simply applied to each VPNv4 route to differentiate them. It does not need to be exchanged between routers, and therefore, a misconfiguration in RD export/import would not prevent route propagation.
Therefore, the most accurate answer is Option B: Misconfiguration in Route Target (RT) export and import, as it directly impacts the ability of PE routers to share VPNv4 routes. Properly configuring the RTs on both the exporting and importing PE routers is essential for correct VPN route propagation in MPLS environments.
Question No 7:
In a Layer 3 MPLS VPN configuration on Cisco IOS XR PE routers, which configuration mode is used to assign an interface to a VRF using the vrf command?
A. RP/0/RP0/CPU0:PE(config-bgp)#
B. RP/0/RP0/CPU0:PE(config-if)#
C. RP/0/RP0/CPU0:PE(config-bgp-af)#
D. RP/0/RP0/CPU0:PE(config-vrf)#
Correct Answer: B. RP/0/RP0/CPU0:PE(config-if)#
Explanation:
In Layer 3 MPLS VPN deployments, VRFs (Virtual Routing and Forwarding instances) are used to separate customer traffic on a shared infrastructure. Cisco IOS XR PE routers enable virtual network segmentation using VRFs, and assigning interfaces to these VRFs is essential for directing traffic based on the respective routing instances.
The vrf command used to link an interface to a specific VRF must be executed in interface configuration mode. This is because VRF binding is a per-interface configuration, ensuring that traffic on each interface is handled within the context of the appropriate VRF.
To assign an interface to a VRF, the user navigates to interface configuration mode. For example:
This command links the interface to the Customer_A VRF, so all traffic received is routed based on the Customer_A VRF table.
Why other options are incorrect:
A (config-bgp) is used for BGP protocol settings, not for interface-VRF assignments.
C (config-bgp-af) is used for address-family specific BGP configuration, not interface-related VRF binding.
D (config-vrf) defines the VRF instance itself but doesn’t associate interfaces to it.
Question No 8:
When configuring a Layer 3 MPLS VPN, which feature must be enabled on the PE routers to transform customer IPv4 prefixes into distinct 96-bit addresses for VRF-based forwarding?
A. RT (Route Target)
B. VC ID (Virtual Circuit Identifier)
C. RD (Route Distinguisher)
D. PW ID (Pseudowire ID)
Correct Answer: C. RD (Route Distinguisher)
Explanation:
In a Layer 3 MPLS VPN setup, customer networks may use overlapping IP address ranges. To distinguish between them within the MPLS backbone, PE routers generate unique 96-bit prefixes using Route Distinguishers (RDs). An RD is a 64-bit value that, when prepended to a 32-bit IPv4 prefix, produces a globally unique VPNv4 route.
This extended route identifier enables the MPLS network to maintain separation between identical IP prefixes from different customers, ensuring accurate routing and traffic segregation across the provider’s core.
Why other options are incorrect:
A RT (Route Target) manages VPN route import/export policies but does not create unique identifiers for prefixes.
B VC ID is relevant for Layer 2 VPNs and pseudowire identification, not VRF-based IP address translation.
D PW ID, like VC ID, is specific to Layer 2 MPLS VPNs and has no role in creating VPNv4 addresses.
Only the RD enables the transformation of overlapping IPv4 customer addresses into globally unique VPNv4 prefixes required for Layer 3 MPLS VPN routing.
Question No 9:
A network engineer is diagnosing connectivity within an MPLS infrastructure and needs to determine whether a Label Switched Path (LSP) between two routers is functioning as intended.
Which diagnostic utility should be employed to accurately test this path?
A. uRPF
B. MPLS LSP ping
C. Logging
D. RSVP
Answer: B. MPLS LSP ping
Explanation:
In a Multiprotocol Label Switching (MPLS) network, ensuring the health and operational accuracy of Label Switched Paths (LSPs) is vital for the efficient delivery of traffic. LSPs are the predetermined forwarding paths established through the MPLS domain, and any disruption or misconfiguration along these paths can lead to significant service degradation or loss.
To verify the integrity and reachability of an LSP, the most effective tool available is the MPLS LSP ping. This mechanism functions similarly to the conventional ICMP ping but is specialized for MPLS environments. It sends labeled echo request packets through the LSP towards a target router, where each hop processes the label and forwards the packet accordingly. The destination router then returns an echo reply, allowing the originating router to confirm whether the LSP is intact and functional.
This diagnostic procedure helps pinpoint issues like incorrect label assignments, broken forwarding paths, or inconsistent routing behavior within the MPLS core. Since the packets follow the same label-switched path that real traffic would take, the results reflect actual forwarding conditions, providing high diagnostic value.
By contrast, uRPF (Unicast Reverse Path Forwarding) is a security measure used to mitigate spoofed IP addresses by ensuring that packets arrive on the correct interface based on routing tables. It does not serve any role in validating MPLS path operations. Logging is a passive tool meant for recording events and system messages, useful for auditing or historical analysis, but not for active testing. RSVP (Resource Reservation Protocol) is responsible for reserving bandwidth for MPLS TE (Traffic Engineering) tunnels, but it does not actively test LSPs.
Thus, to directly assess the performance and status of an LSP, MPLS LSP ping is the most appropriate and specialized tool.
Question No 10:
While deploying a Layer 2 VPN on a Cisco IOS XE router, a network engineer attempts to apply the xconnect command. However, the router returns an error indicating that the cross-connect cannot be established.
Which configuration is most likely missing from the involved interface?
A. encapsulation mpls
B. encapsulation l2tpv3
C. protocol l2tpv3
D. protocol none
Correct Answer: A. encapsulation mpls
Explanation:
The xconnect command is used in Cisco IOS XE to build point-to-point Layer 2 VPN connections across a service provider’s backbone. This technology, often referred to as AToM (Any Transport over MPLS), requires specific configurations on the participating interfaces. One of the most essential is the definition of the correct encapsulation method.
When using MPLS as the transport method, the interface on which the xconnect command is applied must be explicitly configured with encapsulation mpls. This setting prepares the interface to handle Layer 2 frames by wrapping them in MPLS labels, enabling the data to traverse the MPLS core appropriately. Without this encapsulation, the router lacks the instructions to interpret or forward Layer 2 frames over the MPLS infrastructure, which results in errors such as failed xconnect sessions.
Option B (encapsulation l2tpv3) and C (protocol l2tpv3) are relevant only when deploying Layer 2 VPNs using L2TPv3 over IP, not MPLS. If the intention were to use IP-based transport, these settings would be necessary instead of MPLS-related ones. Option D (protocol none) signifies that no protocol is selected on the interface, which renders the xconnect configuration incomplete and unusable.
Therefore, when deploying an MPLS-based Layer 2 VPN using xconnect, omitting encapsulation mpls on the interface will prevent the session from forming. Ensuring the encapsulation matches the intended transport technology is fundamental for successful VPN service deployment in Cisco-based service provider networks.
