350-501 Practice Test 30 — 15 Questions

Question 1

Which TWO commands are most effective to verify that an SR-TE policy is active and forwarding traffic? (Choose two.)

Accepted Answer

show segment-routing traffic-eng policy. Option A, 'show segment-routing traffic-eng policy', is correct because it directly displays the operational state of SR-TE policies, including whether each policy is up/active, its binding SID, and the candidate paths and segment lists in use, which confirms the policy is instantiated and installed. Option C, 'show mpls forwarding-table labels', is correct because it verifies the data plane by showing the incoming label, outgoing label, and next-hop for the policy's binding SID or segment list, proving traffic is actually being forwarded along the SR-TE path. Option B, 'show isis database verbose', only displays IS-IS link-state database contents and does not confirm SR-TE policy state or forwarding. Option D, 'show segment-routing traffic-eng segment-list', shows configured segment lists but not whether a policy is active or forwarding traffic. Option E, 'show bgp labels', displays BGP label bindings and is unrelated to SR-TE policy verification.

Answer

show isis database verbose

Answer

show segment-routing traffic-eng segment-list

Answer

show bgp labels

Question 2

What is the primary difference between traffic policing and traffic shaping?

Accepted Answer

Shaping buffers excess traffic, while policing drops or re-marks it.. Traffic shaping buffers excess packets and delays them to smooth bursts to conform to a rate, while traffic policing drops or re-marks packets that exceed the configured rate. This is the fundamental behavioral difference between the two QoS mechanisms.

Answer

Policing buffers excess traffic, while shaping drops it.

Answer

Policing is only applied inbound, shaping only outbound.

Answer

Both policing and shaping buffer excess traffic.

Question 3

An SP network is migrating from IS-IS narrow metrics to wide metrics. What is a key advantage of using wide metrics?

Accepted Answer

Wide metrics support up to 2^24-1 link cost and TE metrics.. Wide metrics expand the link cost field from the narrow 6-bit value (max 63) to a 24-bit field, allowing costs up to 2^24-1 (16,777,215). This larger range is essential in modern SP networks because it supports Traffic Engineering (TE) metrics and provides enough granularity to differentiate link costs across high-speed interfaces without hitting the narrow metric ceiling.

Answer

Wide metrics are backward compatible with narrow metrics without any configuration.

Answer

Wide metrics reduce SPF computation time.

Answer

Wide metrics enable BFD for faster convergence.

Question 4

In SR-MPLS TE, a headend router is configured with an SR Policy that includes an explicit candidate path with segment list [16001, 16003]. What do these numbers represent?

Accepted Answer

MPLS label values representing Node SIDs or Adjacency SIDs. In SR-MPLS, segment lists are composed of MPLS labels. Node SIDs are typically from the SRGB (e.g., 16001 could be a Node SID for a router). Adjacency SIDs would be link-specific labels. The numbers are labels, not interface indices or metric values.

Answer

Interface indices

Answer

Metric values for path calculation

Answer

IPv4 addresses encoded as numbers

Question 5

An SP is implementing Carrier-Grade NAT (CGNAT) to conserve IPv4 addresses. Which feature must be enabled to support applications that embed IP addresses in the payload, such as SIP or FTP?

Accepted Answer

ALG (Application Layer Gateway). Application Layer Gateway (ALG) is the feature that inspects and rewrites IP addresses and port numbers embedded inside application payloads — such as SIP SDP bodies, FTP PORT/PASV commands, and H.323 — which CGNAT would otherwise break because it only translates IP headers. Without ALG, a SIP client behind CGNAT would advertise its private IP in the SDP, and the remote peer would be unable to route media back. ALG is therefore mandatory for CGNAT deployments supporting such protocols.

Answer

IPSec

Answer

Port forwarding

Answer

NAT traversal

Question 6

A network operator is implementing segment routing (SR-MPLS) using OSPF as the IGP. Which OSPF TLV is used to advertise the Node SID (Prefix SID) for a router's loopback address?

Accepted Answer

Extended Prefix TLV. In OSPFv2 Segment Routing extensions (RFC 8665), the Prefix SID (Node SID) for a router's loopback is advertised inside the OSPF Extended Prefix TLV, which is carried in an OSPF Extended Prefix Opaque LSA (type 7). The Extended Prefix TLV contains the prefix, the prefix length, and the SID/Label sub-TLV that encodes the Node SID index. This is the mechanism that lets other routers in the SR-MPLS domain build the MPLS label stack for the node.

Answer

Router Information TLV

Answer

Traffic Engineering TLV

Answer

Extended Link TLV

Question 7

A service provider is automating QoS policy deployment using Cisco NSO and YANG. During validation, the engineer discovers that the pushed policy is not taking effect. Which three possible causes should be investigated? (Choose three.)

Accepted Answer

The device does not support the YANG model used. Cisco NSO uses YANG models to translate service definitions into device-specific CLI or NETCONF operations. If the target device does not support the YANG model referenced in the service package, the NETCONF or CLI operations will fail silently or produce no effect, as the device cannot interpret the configuration intent. This is a common validation failure when using model-driven orchestration with heterogeneous device populations.

Answer

The device has a feature license missing for QoS

Answer

The policy-map name conflicts with an existing one

Question 8

A service provider is planning to offer L2VPN services using MPLS. Which TWO statements are true regarding Ethernet over MPLS (EoMPLS) and Virtual Private LAN Service (VPLS)?

Accepted Answer

EoMPLS provides a point-to-point pseudowire between two PE routers.. Option A is correct because Ethernet over MPLS (EoMPLS) in its basic form establishes a point-to-point pseudowire (a virtual circuit, often signaled via LDP or BGP) between two PE routers, carrying Ethernet frames across the MPLS core. Option D is correct because VPLS (Virtual Private LAN Service) emulates a multipoint-to-multipoint Ethernet LAN over the MPLS network, allowing multiple sites to appear as if connected to the same Ethernet segment. Option B is wrong because VPLS does not require all PE routers to be in the same VLAN; it uses VPLS instances and MPLS labels to separate customer traffic, not a shared VLAN. Option C is wrong because VPLS uses a full-mesh of pseudowires between PE routers (or a hierarchical/ H-VPLS variant), not a hub-and-spoke topology. Option E is wrong because MAC address learning between sites is a characteristic of VPLS (multipoint), whereas basic EoMPLS point-to-point pseudowires do not perform MAC learning across multiple sites.

Answer

VPLS requires all PE routers to be in the same VLAN.

Answer

VPLS uses a hub-and-spoke topology to interconnect multiple sites.

Answer

EoMPLS supports MAC address learning between sites.

Question 9

In an MPLS L3VPN network, a route reflector (RR) is used to distribute VPNv4 routes between PE routers. After a new PE router (PE4) is added, some VPN routes are not being received by other PEs. Which TWO actions should be investigated to resolve the issue? (Choose two.)

Accepted Answer

Ensure the VRF route-target import/export values are correctly configured on the new PE.. Option A is correct because in an MPLS L3VPN, a PE only imports a VPNv4 route into a VRF when the route's route-target extended community matches the VRF's import route-target; if PE4's VRF import/export values are wrong, routes will not be installed or advertised correctly, so the RT configuration must be verified. Option C is correct because VPNv4 routes are exchanged over the BGP session between PE4 and the RR; if the BGP VPNv4 neighbor relationship (address-family vpnv4 unicast) is not Established, PE4 will neither send nor receive VPNv4 prefixes, which directly explains missing routes. Option B is not appropriate because OSPF is an IGP used for reachability inside the provider core, not for redistributing VPNv4 routes; adding it would not fix VPNv4 route distribution. Option D is less relevant because although physical/IGP reachability is needed for the BGP session, the scenario already implies the RR is functioning and the specific issue is VPN route propagation, making the BGP VPNv4 session and RT configuration the direct checks. Option E is not the right action because a route refresh only re-requests advertisements over an existing session and does not fix a missing or misconfigured VPNv4 session or incorrect route-targets.

Answer

Configure OSPF as an additional IGP to redistribute VPN routes.

Answer

Check physical connectivity and IGP adjacency between the new PE and the RR.

Answer

Issue a 'clear ip bgp * refresh' on the RR.

Question 10

A service provider is using LISP to provide host mobility. Which LISP component is responsible for storing the mapping of EID to RLOC?

Accepted Answer

Map-Server. In LISP (RFC 6830), the Map-Server (MS) is the central repository that stores the mapping of Endpoint Identifiers (EIDs) to Routing Locators (RLOCs). When an Ingress Tunnel Router (ITR) needs to forward traffic to a destination EID, it queries the Map-Resolver, which in turn contacts the Map-Server to retrieve the authoritative mapping. The Map-Server also accepts registration from Egress Tunnel Routers (ETRs) on behalf of their EID prefixes, making it the definitive source for EID-to-RLOC bindings.

Answer

Altitude

Answer

Tunnel Router

Answer

Map-Resolver

Question 11

A service provider is implementing hierarchical QoS on an edge router. The goal is to shape the aggregate traffic to 100 Mbps and then apply different queuing policies for voice and data within that shaped pipe. Which configuration approach is correct?

Accepted Answer

Configure a parent policy-map with shape and a child policy-map with queuing, then apply the child under the parent's class.. Hierarchical QoS in Cisco IOS uses a nested policy-map structure: the parent policy-map contains the shaping action (e.g., shape average 100000000) and references a child policy-map via the 'service-policy' command inside the class. The child policy-map contains the queuing actions (e.g., priority for voice, bandwidth for data). This creates a shaper with a nested queuing hierarchy, which is the correct way to shape aggregate traffic and then queue within the shaped pipe.

Answer

Apply shaping on the interface and queuing on a subinterface separate from the policy-map.

Answer

Use a child policy-map for shaping and a parent policy-map for queuing.

Answer

Apply a single policy-map with both shape and queue commands under the same class.

Question 12

A large SP network uses Segment Routing (SR) with MPLS data plane. They want to enforce a strict path for certain traffic flows across the core while using shortest-path for others. Which technique should be used?

Accepted Answer

SR-TE with explicit path using segment list. SR-TE with an explicit path using a segment list allows the operator to define a strict, ordered list of MPLS labels (segments) that the traffic must follow, overriding the default IGP shortest-path behavior. This is the correct technique for enforcing a strict path across the core while leaving other traffic to use shortest-path forwarding.

Answer

Using TI-LFA

Answer

Configuring bandwidth reservation on all links

Answer

Using SR policies with color extended community based on BGP

Question 13

Match each MPLS VPN technology to its description.

Accepted Answer

MPLS Layer 3 VPN: Uses BGP to distribute customer routes between PE routers. MPLS provides multiple VPN services: Layer 3 VPNs use BGP for route exchange, Layer 2 VPNs emulate L2 circuits, TE controls traffic paths, and Inter-AS extends connectivity across providers. Common confusions involve swapping the L2 and L3 definitions.

Answer

MPLS Layer 3 VPN: Provides transparent transport of Layer 2 frames

Answer

MPLS Layer 2 VPN: Uses BGP to distribute customer routes between PE routers

Question 14

Refer to the exhibit. The output shows an MPLS forwarding entry with FRR protection. What is the purpose of the backup path shown?

Accepted Answer

To forward traffic if the primary outgoing interface fails.. The backup path in an MPLS Fast Reroute (FRR) configuration is precomputed and installed in the forwarding table to provide sub-50ms protection against link or node failures. When the primary outgoing interface fails, traffic is immediately switched to the backup path without waiting for IGP convergence, ensuring minimal packet loss.

Answer

To handle penultimate hop popping for the primary path.

Answer

To provide a load-balancing alternative for the primary path.

Answer

To carry the VPN label separately.

Question 15

Which three components are part of NSO (Network Services Orchestrator) architecture? (Choose three.)

Accepted Answer

YANG models for service definitions. YANG models are the foundation for service definitions in NSO because they define the data structures and constraints for network services using a standardized modeling language (RFC 6020/7950). NSO uses YANG to model both the service layer (customer-facing services) and the device layer (native device configurations), enabling service abstraction and multi-vendor orchestration.

Answer

RADIUS server

Answer

PCEP (Path Computation Element Protocol)