350-501 Practice Test 48 — 15 Questions

Question 1

A network engineer is configuring a Cisco router to participate in an MPLS L3VPN. The router is a PE that must exchange VPNv4 routes with other PE routers. Which address family must be activated in BGP to support this?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

VPNv4 address family. For MPLS L3VPN, PE routers exchange VPNv4 routes using BGP. The VPNv4 address family must be activated under BGP to carry the route distinguisher and route target extended communities. Other address families like IPv4 unicast or L2VPN serve different purposes and do not support the necessary attributes for L3VPN.

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IPv4 multicast address family

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L2VPN address family

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IPv4 unicast address family

Question 2

A service provider is implementing MPLS Traffic Engineering (TE) with RSVP-TE in its core network. The network uses OSPF as the IGP. The provider wants to ensure that TE tunnels are established over paths that meet specific bandwidth constraints. Which OSPF LSA type carries the TE information required for path computation?

Accepted Answer

Type 10 Opaque LSA. OSPF Traffic Engineering uses Type 10 Opaque LSAs to distribute TE parameters such as available bandwidth, affinity, and administrative groups. These LSAs are flooded within the OSPF area and are used by the CSPF algorithm to compute paths that satisfy the constraints for RSVP-TE tunnels. The other LSA types do not carry TE information and cannot be used for TE path computation.

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Type 1 Router LSA

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Type 5 AS External LSA

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Type 2 Network LSA

Question 3

A service provider is deploying a BGP-based MPLS L3VPN. The PE routers are configured with VRFs and MP-BGP for VPNv4. A customer reports that routes from one site are not being installed in the VRF of another site, even though the VPNv4 routes are present on the remote PE. Which BGP feature must be configured to allow the PE to import the VPNv4 routes into the correct VRF?

Accepted Answer

Route Target (RT) export and import. Route Targets are used to control the import and export of VPNv4 routes into VRFs. The exporting PE attaches an RT to the route, and the importing PE imports the route into any VRF that has a matching import RT. Without the correct RT import configuration, the route is not installed in the VRF, even though it exists in the BGP table. Therefore, RT import must be configured.

Answer

MP-BGP Capability Negotiation

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Route Distinguisher (RD)

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BGP Extended Communities

Question 4

A service provider is deploying MPLS Traffic Engineering (TE) with RSVP-TE in its core. The network uses OSPF as the IGP. The engineer notices that TE tunnels are not being established because the headend router does not have the TE database populated with link attributes. Which OSPF LSA type is responsible for carrying TE information in this scenario?

Accepted Answer

Type 10 LSA (Area-Local Opaque LSA). OSPF Traffic Engineering uses Type 10 opaque LSAs (area-local) to distribute TE link attributes. These LSAs are generated by routers with MPLS TE enabled and include parameters like maximum bandwidth, reservable bandwidth, and administrative groups. The headend router uses this information to compute constrained paths. Without Type 10 LSAs, the TE database is empty, and RSVP-TE tunnels cannot be established.

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Type 11 LSA (AS-Wide Opaque LSA)

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Type 5 LSA (AS External LSA)

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Type 9 LSA (Link-Local Opaque LSA)

Question 5

A service provider is using Segment Routing with MPLS data plane. The IGP is OSPFv2. An engineer needs to configure a router to advertise its Segment Routing Global Block (SRGB) and prefix-SIDs. Which OSPF configuration is required?

Accepted Answer

Enable segment-routing mpls under the global configuration and configure the SRGB and prefix-SID under the OSPF process.. Segment Routing with MPLS requires enabling segment-routing mpls globally and then configuring the SRGB and prefix-SIDs within the OSPF process. This allows OSPF to advertise the SR capabilities and prefix-SID sub-TLVs to neighbors. Adjacency SIDs are allocated automatically, and BGP is not used for IGP prefix-SID distribution.

Answer

Enable segment-routing mpls under the global configuration and configure adjacency SIDs under the OSPF process.

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Enable segment-routing mpls under the global configuration and configure prefix-sid under each OSPF interface.

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Enable segment-routing mpls under the global configuration and configure the SRGB and prefix-SID under BGP.

Question 6

An engineer is troubleshooting an MPLS L3VPN where a PE router is not importing routes into the correct VRF. The PE receives VPNv4 routes with route target 65000:100, but the VRF 'CUSTOMER_A' is configured with route target 65000:200. What is the most likely result?

Accepted Answer

The routes will not be imported into any VRF and will be discarded.. Route targets control the import and export of VPNv4 routes into VRFs. If the route target on the received route does not match any import target in the VRF, the route is not imported and is discarded. The route distinguisher only ensures uniqueness and does not affect import. Automatic rewriting is not a default behavior.

Answer

The routes will be imported into CUSTOMER_A after the route target is automatically rewritten to 65000:200.

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The routes will be imported into the global routing table.

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The routes will be imported into CUSTOMER_A because the route distinguisher matches.

Question 7

A service provider is deploying BGP in its core network. The design requires fast convergence and high availability. Which two BGP features should be implemented to achieve sub-second failure detection and to minimize traffic loss? (Choose two.)

Accepted Answer

BGP Next-Hop Tracking (NHT) with IGP fast convergence. To achieve sub-second failure detection and minimize traffic loss, BGP Next-Hop Tracking with IGP fast convergence and BGP Prefix Independent Convergence (PIC) are essential. NHT quickly detects next-hop failures and invalidates routes, while PIC precomputes backup paths for immediate failover. Together, they enable rapid reconvergence without waiting for full BGP convergence.

Answer

BGP Graceful Restart

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BGP Route Refresh Capability

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BGP Additional Paths

Question 8

An engineer is configuring MPLS LDP on a Cisco router. The router must only advertise label bindings for prefixes that are in the global routing table and must not allocate labels for prefixes learned from a specific customer VRF. Which LDP feature should be configured?

Accepted Answer

LDP label allocation filter. The LDP label allocation filter is used to control which prefixes are assigned labels. By applying a filter, the router can allocate labels only for prefixes that are in the global routing table and avoid allocating labels for prefixes from a specific VRF. This directly addresses the requirement to restrict label bindings to global prefixes and exclude VRF prefixes.

Answer

LDP IGP synchronization

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LDP session protection

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LDP explicit-null

Question 9

A service provider is deploying Segment Routing over an MPLS core using OSPFv2 as the IGP. The network engineer must configure the routers to support SR-MPLS and ensure that adjacency SIDs are generated for all core links. Which two configuration steps are required on each router? (Choose two.)

Accepted Answer

Enable 'segment-routing mpls' globally.. To enable SR-MPLS with OSPF, you must enable segment routing globally and within the OSPF process. The global command activates SR and allocates SID blocks. The OSPF command enables the advertisement of SIDs via OSPF LSAs. Adjacency SIDs are then automatically generated for links where SR is enabled. LDP and RSVP-TE are not used in this context. A prefix SID for the loopback is important for prefix SIDs but not for adjacency SIDs.

Answer

Configure 'mpls ldp' on all core interfaces.

Answer

Configure a prefix SID for the loopback interface.

Answer

Enable 'mpls traffic-eng tunnels' on all core interfaces.

Question 10

A service provider is using BGP for its MPLS L3VPN service. The network engineer wants to ensure that the PE routers can forward traffic using the correct label stack. Which BGP attribute is used to carry the MPLS label in VPNv4 route advertisements?

Accepted Answer

MP_REACH_NLRI. In BGP VPNv4 route advertisements, the MPLS label is encoded within the NLRI field of the MP_REACH_NLRI attribute. This attribute is used for multiprotocol BGP extensions, including VPNv4. The label is part of the prefix information, allowing the receiving PE to use it for forwarding. Other attributes like EXTENDED_COMMUNITIES, AS_PATH, and LOCAL_PREF serve different purposes and do not carry the label.

Answer

LOCAL_PREF

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AS_PATH

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EXTENDED_COMMUNITIES

Question 11

A service provider is troubleshooting an MPLS L3VPN where a customer reports that traffic from Site A to Site B is being dropped. The provider verifies that the VPNv4 route for Site B's prefix is present on the ingress PE, but the MPLS label stack is missing the VPN label. Which action should be taken to resolve this?

Accepted Answer

Verify that the egress PE has advertised a VPN label for the prefix in the VRF address family.. In MPLS L3VPN, the VPN label is allocated by the egress PE and distributed via MP-BGP. If the ingress PE has the VPNv4 route but no VPN label, the egress PE is not advertising one, which prevents the ingress PE from building the correct label stack. Verifying label allocation and advertisement on the egress PE resolves the issue. LDP, static labels, and PHP do not affect VPN label signaling.

Answer

Enable LDP on the PE-CE interface to distribute labels for the customer prefix.

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Disable penultimate hop popping on the penultimate router to preserve the VPN label.

Answer

Configure a static MPLS label on the ingress PE for the customer prefix.

Question 12

A service provider is deploying RSVP-TE in its MPLS core. An engineer is configuring a TE tunnel from R1 to R4 with a specific bandwidth requirement. The path computation must avoid a specific link due to maintenance. Which RSVP-TE object is used in the Path message to specify the explicit route?

Accepted Answer

ERO (Explicit Route Object). The ERO is the RSVP-TE object that specifies the explicit route for a TE tunnel. It is included in the Path message and contains the list of hops the tunnel must traverse. While XRO can exclude links, it is not used to specify the explicit route; it is used in conjunction with ERO for exclusion.

Answer

SERO (Secondary Explicit Route Object)

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XRO (Exclude Route Object)

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RRO (Record Route Object)

Question 13

A service provider is deploying MPLS L3VPN with BGP route reflectors. The route reflectors are configured with the bgp cluster-id command. What is the primary purpose of this command?

Accepted Answer

To prevent routing loops by identifying the cluster in the CLUSTER_LIST attribute.. The 'bgp cluster-id' command assigns a cluster ID that is inserted into the CLUSTER_LIST attribute of reflected routes. This allows route reflectors to detect and prevent loops by checking if their own cluster ID is already present. It is a loop prevention mechanism, not for session establishment, AS_PATH manipulation, or enabling route reflection.

Answer

To define the autonomous system number used in the AS_PATH.

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To specify the router ID of the route reflector for BGP session establishment.

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To enable route reflection for a specific address family.

Question 14

A service provider network uses OSPF as the IGP. An engineer is troubleshooting a routing issue and notices that a router is not installing a route to a specific network in its routing table, even though the network is advertised by a neighbor. The engineer suspects a filter is applied. Which OSPF feature can be used to filter routes from being installed in the routing table without affecting the link-state database?

Accepted Answer

Distribute-list. Distribute-list is the OSPF feature that filters routes from being installed in the routing table. It can be applied inbound to prevent local installation or outbound to prevent advertisement. It operates on the routing table, not the LSDB, so LSAs are still flooded and the LSDB remains unchanged.

Answer

Area range

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Stub area

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Virtual link

Question 15

A service provider is migrating its MPLS backbone from LDP to Segment Routing (SR) with MPLS data plane. The network currently uses LDP for label distribution. The provider wants to ensure uninterrupted MPLS forwarding during the migration. Which step should be taken first to allow SR and LDP to coexist and avoid traffic disruption?

Accepted Answer

Enable SR and LDP on all routers, allowing them to coexist and advertise labels for the same prefixes.. To migrate from LDP to SR without disruption, the recommended approach is to enable both SR and LDP on all routers in the MPLS domain. This allows routers to maintain label forwarding using LDP while SR is being introduced. Once SR is fully operational and all routers have SR labels, LDP can be gradually disabled. This coexistence phase ensures that traffic is not disrupted due to missing labels. Disabling LDP abruptly or enabling SR only on a subset of routers would cause forwarding breaks.

Answer

Disable LDP on all routers and enable SR simultaneously.

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Configure SR only on the core routers and keep LDP on the edge routers.

Answer

Enable SR globally and configure SRGB to match the existing LDP label range.