350-501 Practice Test 31 — 15 Questions

Question 1

A service provider needs to offer L3VPN services with customer isolation. Which technology is used to maintain separate routing tables for different customers on a single PE router?

Accepted Answer

VRF. A VRF (Virtual Routing and Forwarding) instance creates a separate virtual routing table on the PE router, allowing multiple customers to share the same physical device while keeping their routing information completely isolated. Each VRF maintains its own RIB and FIB, so overlapping IP address spaces between customers do not conflict. This is the foundational mechanism for L3VPN customer isolation on a single PE.

Answer

VLAN

Answer

Route distinguisher (RD)

Answer

MPLS labels

Question 2

In an MPLS-TE tunnel configuration, which RSVP message carries the Explicit Route Object (ERO) that specifies the explicit path the tunnel must follow?

Accepted Answer

PATH message. In MPLS-TE with RSVP-TE, the PATH message is sent downstream from the ingress LER toward the egress and carries the Explicit Route Object (ERO) that lists the hops the tunnel must traverse. The RESV message is sent back upstream to reserve resources and carries the Label Request/RRO, not the ERO.

Answer

RSVP_TEAR message

Answer

RSVP_ERR message

Answer

RESV message

Question 3

A network engineer needs to ensure that a specific customer's traffic is not adversely affected by other customers' traffic in a shared MPLS core. Which technology should be used?

Accepted Answer

QoS policies on PE routers with shaping and policing. QoS policies on PE routers with shaping and policing allow the service provider to enforce traffic contracts per customer, ensuring that one customer's traffic does not consume bandwidth allocated to another. This is achieved by applying ingress policing to limit customer traffic to the Committed Information Rate (CIR) and egress shaping to smooth bursts, preventing congestion in the MPLS core from affecting other customers.

Answer

iBGP route reflectors

Answer

MPLS Traffic Engineering

Answer

802.1Q VLANs

Question 4

Which two protocols are commonly used for label exchange in an MPLS network? (Choose two.)

Accepted Answer

LDP. LDP (Label Distribution Protocol) is correct because it is the standard protocol designed specifically to distribute MPLS labels between adjacent Label Switch Routers, binding a label to each FEC so that LSRs can forward packets along label-switched paths. BGP is also correct because BGP, when extended with the labeled-unicast address family (RFC 3107), can distribute MPLS labels along with prefixes, which is essential for inter-AS MPLS and BGP-based MPLS VPNs (e.g., VPNv4/VPNv6 with route targets). OSPF and IS-IS are link-state routing protocols that distribute IP reachability information and can carry MPLS TE extensions (opaque LSAs/TLVs) for traffic engineering, but they do not themselves exchange MPLS labels. PIM is a multicast routing protocol used to build multicast distribution trees and has no role in label distribution.

Answer

OSPF

Answer

PIM

Answer

IS-IS

Question 5

Which TWO statements about model-driven telemetry compared to SNMP are correct? (Choose two.)

Accepted Answer

Model-driven telemetry can stream data at sub-second intervals.. Model-driven telemetry (MDT) uses a push model where the network device streams structured data (e.g., YANG-modeled) to a collector, enabling sub-second intervals for real-time monitoring. This contrasts with SNMP's pull model, where the manager polls the device at intervals limited by CPU and network overhead, making sub-second polling impractical.

Answer

Model-driven telemetry uses UDP for transport by default.

Answer

Model-driven telemetry only sends data on change (event-driven).

Answer

Model-driven telemetry uses MIBs to define data structures.

Question 6

Which protocol is used by a BNG to authenticate and authorize subscribers?

Accepted Answer

RADIUS. RADIUS (Remote Authentication Dial-In User Service) is the standard AAA protocol used by Broadband Network Gateways (BNGs) to authenticate and authorize subscribers, typically via PPPoE or IPoE sessions. The BNG acts as a RADIUS client, sending Access-Request messages to a RADIUS server that returns Access-Accept with attributes such as Framed-IP-Address, Session-Timeout, and QoS profiles. This is the canonical deployment in carrier broadband networks.

Answer

DIAMETER

Answer

LDAP

Answer

TACACS+

Question 7

A network engineer is troubleshooting an OSPF adjacency issue between two routers connected via a serial link. The routers are configured with point-to-point network type. The adjacency stays in EXSTART state. What is the most likely cause?

Accepted Answer

Mismatched MTU.. On a point-to-point OSPF link, the EXSTART state indicates that the routers have formed a bidirectional communication (2WAY) and are now negotiating the master/slave relationship for database description (DBD) packet exchange. A mismatched MTU between the two interfaces causes the DBD packets to be dropped or rejected, preventing the adjacency from progressing beyond EXSTART. This is a common issue on serial links where one side may have a different MTU configured.

Answer

Mismatched OSPF area ID.

Answer

Mismatched hello/dead intervals.

Answer

Duplicate router IDs.

Question 8

A metro Ethernet provider needs to scale customer VLANs beyond the 4,096 limit by encapsulating customer VLAN tags with an outer service provider tag. Which IEEE standard is used?

Accepted Answer

802.1ad (Q-in-Q). IEEE 802.1ad, commonly known as Q-in-Q or provider bridging, defines the encapsulation of customer VLAN tags (C-TAGs) with an outer service provider VLAN tag (S-TAG). This allows a provider to scale beyond the 4,096 VLAN limit by using the outer tag to identify customer traffic while preserving the inner customer VLAN tag.

Answer

802.1ah (Provider Backbone Bridging)

Answer

802.1Q

Answer

802.1ak

Question 9

An engineer is troubleshooting a QoS policy on a Cisco router. The policy is intended to mark voice traffic with DSCP EF and video traffic with DSCP AF41. After applying the policy, voice traffic is correctly marked, but video traffic is marked as DSCP 0. What is the most likely cause?

Accepted Answer

The class map for video traffic does not match the traffic correctly.. The most common reason for video traffic being marked as DSCP 0 (default) while voice traffic is correctly marked is that the class map for video traffic fails to match the intended packets. This could be due to an incorrect match statement (e.g., using the wrong ACL, protocol, or DSCP value) or a misconfigured match criterion that does not capture the video flows. Since voice traffic is marked correctly, the policy itself is applied and functional, isolating the issue to the video class map's matching logic.

Answer

The video traffic is being policed and dropped.

Answer

The trust boundary is set to 'trust dscp' and the incoming video traffic is not marked.

Answer

The policy is not applied to the correct interface direction.

Question 10

A service provider has deployed QoS on its MPLS backbone to offer different classes of service. The provider notices that EF (Expedited Forwarding) traffic sometimes experiences high jitter during congestion. Following recommended practices, which action is MOST likely to reduce jitter for EF traffic?

Accepted Answer

Use priority queuing (LLQ) for EF traffic with a policer. Priority queuing (LLQ) with a policer ensures EF traffic is served strictly before other queues, reducing jitter, while the policer prevents EF traffic from monopolizing bandwidth. Option B is wrong because traffic shaping smooths bursts but does not provide priority treatment during congestion, so jitter can still occur. Option C is wrong because changing DSCP to AF41 would reclassify EF traffic to a lower priority class, potentially increasing jitter and delay. Option D is wrong because WRED is a congestion avoidance mechanism that drops packets randomly, which can cause jitter for EF traffic; EF should be exempt from WRED.

Answer

Apply traffic shaping on all EF packets at the edge

Answer

Change the DSCP value of EF traffic to AF41 to reduce drops

Answer

Apply weighted random early detection (WRED) on the EF queue

Question 11

Which EVPN component ensures that only one of the multi-homed PEs forwards traffic to the CE for a given Ethernet segment?

Accepted Answer

DF Election. Designated Forwarder (DF) Election is the EVPN mechanism defined in RFC 7432 that elects one PE per Ethernet Segment (identified by ESI) to forward broadcast, unknown unicast, and multicast (BUM) traffic toward the CE. This prevents duplicate frame delivery to a multi-homed CE when multiple PEs are attached to the same segment. The election is based on a deterministic algorithm using the ESI and PE addresses, and the DF role can be per-VLAN or per-EVI.

Answer

Split Horizon

Answer

Aliasing

Answer

ESI (Ethernet Segment Identifier)

Question 12

In BGP, an SP router receives multiple routes to the same prefix. The first route has a weight of 100, LOCAL_PREF of 200, AS_PATH length 3, and is learned via eBGP. The second route has weight 50, LOCAL_PREF 150, AS_PATH length 2, and is learned via iBGP. According to BGP route selection, which route will be preferred?

Accepted Answer

The first route (weight 100). BGP selection order: highest weight first. Route 1 has weight 100, Route 2 has weight 50, so Route 1 is preferred regardless of other attributes.

Answer

The second route (AS_PATH length 2)

Answer

The first route (eBGP learned)

Answer

The second route (LOCAL_PREF 150)

Question 13

A service provider plans to deploy automation using Cisco NSO. Which two benefits does NSO provide for service lifecycle management? (Choose two.)

Accepted Answer

Automatic rollback on failed deployment.. Option A is correct because Cisco NSO maintains a transactional configuration model and, when a service deployment or commit fails, it can automatically roll back to the previous known-good configuration state, which is a core benefit for reliable service lifecycle management. Option B is correct because NSO uses Network Element Drivers (NEDs) to support multi-vendor devices, communicating via protocols such as NETCONF, CLI, RESTCONF, and SNMP, enabling a single automation platform across heterogeneous networks. Option C is not correct because NSO is an orchestration platform that runs externally and does not provide an on-device scripting engine. Option D is not correct because real-time traffic monitoring is not a primary NSO service lifecycle management benefit; that is typically handled by telemetry or monitoring tools. Option E is not correct because while compliance can be implemented through NSO services and policies, built-in configuration compliance checks are not one of the two primary benefits listed for service lifecycle management in this context.

Answer

On-device scripting engine.

Answer

Real-time traffic monitoring.

Answer

Built-in configuration compliance checks.

Question 14

In a service provider network, the access layer connects end customers. Which technology is commonly used for fibre-based access in GPON deployments?

Accepted Answer

GPON. GPON (Gigabit Passive Optical Network) is a fibre-based access technology standardized by ITU-T.

Answer

DSL

Answer

MPLS

Answer

Metro Ethernet

Question 15

An SP network engineer is designing a new segment routing traffic engineering deployment within a single IGP area. The network consists of 50 core routers running IS-IS and MPLS. The engineer needs to steer traffic from Router A to Router D over a path that avoids high latency links. Which technology should be used to define and instantiate the explicit path?

Accepted Answer

Configure an SR-TE policy with an explicit path using segment lists.. Segment Routing Traffic Engineering (SR-TE) policies allow an explicit path to be defined as an ordered list of segments (SIDs), which the headend router instantiates as a label stack. This steers traffic from Router A to Router D along a chosen path that avoids high-latency links, within a single IS-IS/MPLS domain. SR-TE is the purpose-built mechanism for explicit path steering in an SR deployment.

Answer

Use LDP to distribute labels and rely on IGP shortest path.

Answer

Set up a Path Computation Element (PCE) and delegate path computation.

Answer

Implement BGP LU to create an explicit path via local policies.