350-501 Practice Test 18 — 15 Questions

Question 1

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.)

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

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 2

Which technology allows an IPv6-only customer edge router to connect to an MPLS provider edge router using IPv4 transport, encapsulating IPv6 packets in MPLS with a labeled IPv4 next-hop?

Accepted Answer

6PE. 6PE (IPv6 Provider Edge) uses MP-BGP to exchange IPv6 prefixes with IPv4 next-hop addresses over MPLS. It does not require IPv6 in the core.

Answer

6VPE

Answer

NAT64

Answer

MAP-T

Question 3

A service provider is migrating from OSPF to IS-IS in the core network. They need to support Traffic Engineering and Segment Routing. Which IS-IS TLV must be supported to carry TE information?

Accepted Answer

TLV 22. IS-IS TLV 22 (Extended IS reachability) carries TE metrics and other attributes for traffic engineering. TLVs 128 and 130 are IP reachability TLVs; TLV 135 is for extended IP reachability.

Answer

TLV 130

Answer

TLV 135

Answer

TLV 128

Question 4

In OSPFv3, which statement correctly describes how OSPFv3 differs from OSPFv2 regarding router IDs and adjacencies?

Accepted Answer

OSPFv3 uses a 32-bit Router ID independent of IPv6 addresses.. OSPFv3 uses a 32-bit Router ID independent of IPv6 addresses. Adjacencies are formed with Router IDs, not link-local addresses. OSPFv3 runs per-link rather than per-subnet.

Answer

OSPFv3 uses the same LSA types as OSPFv2.

Answer

OSPFv3 requires both IPv4 and IPv6 addresses on interfaces.

Answer

OSPFv3 uses IPv6 addresses to form adjacencies.

Question 5

In BGP route selection, when comparing two routes with the same LOCAL_PREF, which attribute is considered next?

Accepted Answer

Locally originated routes (prefer routes originated by the local router). After LOCAL_PREF, the next step in BGP best path selection is whether the route was originated locally (via network or aggregate command). Then AS_PATH length is considered.

Answer

MED

Answer

AS_PATH length

Answer

eBGP over iBGP

Question 6

Which BGP attribute is used to influence inbound traffic to a multi-homed AS by indicating the preferred entry point?

Accepted Answer

MED. MED (Multi-Exit Discriminator) is used to influence inbound traffic from neighboring ASes by suggesting the preferred path into the AS.

Answer

AS_PATH

Answer

COMMUNITY

Answer

LOCAL_PREF

Question 7

In an IS-IS network, a service provider wants to achieve fast convergence using Partial Route Computation (PRC). Which of the following events triggers a PRC instead of a full SPF?

Accepted Answer

An IP prefix is withdrawn from a directly connected network. PRC is triggered when an IP prefix changes (addition, removal, or metric change) without a change in the IS-IS topology (i.e., no change in adjacency or reachable IS-IS neighbors). PRC only recalculates the affected prefixes, avoiding full SPF.

Answer

A router's system ID changes

Answer

An LSP with a new fragment arrives

Answer

A new adjacency is formed between two routers

Question 8

A service provider needs to prioritize voice traffic over best-effort data in an MPLS VPN. The PE router uses a QoS policy applied to the ingress interface. Which action ensures that voice packets are marked with the correct DSCP value before entering the MPLS core?

Accepted Answer

Apply a policy-map that matches voice traffic using a class-map and the 'set dscp ef' action.. The question specifies that the PE router must mark voice packets with the correct DSCP value before they enter the MPLS core. The 'set dscp ef' action in a policy-map applied to the ingress interface explicitly sets the DSCP field to EF (46) for voice traffic matched by a class-map, ensuring proper classification and treatment across the MPLS network. This is the standard method for marking IP packets at the edge before MPLS encapsulation.

Answer

Configure the ingress interface with 'mls qos trust dscp' to preserve the customer marking.

Answer

Use a policy-map with the 'set mpls experimental 5' command.

Answer

Apply a police action to drop traffic exceeding the voice bandwidth.

Question 9

Which BGP attribute is used to indicate the preference of a route within an AS and is propagated to iBGP peers but not to eBGP peers by default?

Accepted Answer

LOCAL_PREF. LOCAL_PREF is a well-known discretionary attribute that indicates the degree of preference for a route within an AS. It is sent to iBGP peers but not to eBGP peers by default.

Answer

WEIGHT

Answer

MED

Answer

AS_PATH

Question 10

An SP engineer implements LLQ for VoIP traffic on a DS3 link. The policy-map calls for a priority queue of 500 kbps. The actual VoIP traffic averages 400 kbps with bursts to 600 kbps. What is the expected behavior during bursts?

Accepted Answer

The priority queue drops all traffic above the configured 500 kbps during the burst.. C is correct because the priority queue in a Low Latency Queueing (LLQ) policy is policed at the configured rate (500 kbps). When VoIP traffic bursts exceed this rate, the excess packets are dropped immediately by the policer, not queued or reclassified. This ensures that the priority queue does not starve other queues and maintains low latency for conforming traffic.

Answer

The excess traffic is reclassified to best-effort and placed in the default queue.

Answer

The priority queue uses tail-drop and discards only when the queue is full.

Answer

The excess traffic is queued in the priority queue until bandwidth is available.

Question 11

An SP engineer is troubleshooting IS-IS routing. The network uses wide metrics, and some links have been configured with TE metrics. Which statement correctly describes the relationship between TE metrics and narrow metrics in IS-IS?

Accepted Answer

Wide metrics allow values up to 2^24 - 1, while narrow metrics allow up to 63.. IS-IS supports both narrow (6-bit) and wide (24-bit) style metrics. TE metrics are separate TLVs that carry additional information for MPLS-TE and do not replace the standard metric used for SPF computation.

Answer

Narrow metrics are used only for L1 routes, while TE metrics are used for L2.

Answer

TE metrics override narrow metrics for SPF calculations.

Answer

TE metrics are used by default when metric-style wide is configured.

Question 12

An SP engineer is designing an OSPF network with several remote sites that should not receive external routes but need to reach external destinations via a default route. Which OSPF area type best meets this requirement while also preventing Type 5 LSAs from entering?

Accepted Answer

Totally stubby area. A totally stubby area blocks Type 5 and Type 3 LSAs (except a default route). A stub area blocks Type 5 but allows Type 3 (inter-area routes). An NSSA allows Type 7 LSAs for external routes from the area. A totally stubby area is the correct choice because it blocks both Type 5 and Type 3 (except default), meeting the requirement.

Answer

NSSA

Answer

Backbone area 0

Answer

Stub area

Question 13

In an OSPF network, an area is configured as a Not-So-Stubby Area (NSSA). Which statement about LSA types in this area is correct?

Accepted Answer

Type 7 LSAs are originated by ASBR within the NSSA and converted to Type 5 by the ABR.. NSSA areas allow Type 7 LSAs to carry external routes, which are translated to Type 5 at the ABR. Type 5 LSAs are not allowed within the NSSA, and Type 4 LSAs are also blocked. Type 3 LSAs (summary) are allowed.

Answer

Type 1 and Type 2 LSAs are not allowed in NSSA.

Answer

Type 4 LSAs are used to advertise the ABR to other areas.

Answer

Type 5 LSAs are flooded within the NSSA.

Question 14

Which THREE actions can help mitigate the impact of BGP prefix flapping in a service provider network?

Accepted Answer

Use route summarization.. Route summarization (A) reduces the number of BGP prefixes advertised, which inherently limits the impact of flapping because a single summary prefix represents many more-specific prefixes. If a specific subprefix flaps, the aggregate remains stable, preventing the flapping from propagating to BGP peers. This is a proactive approach to minimize the control-plane churn caused by unstable routes.

Answer

Use BGP peer groups.

Answer

Apply BGP graceful restart.

Question 15

Which THREE factors must be considered when deploying MPLS Layer 3 VPN services to ensure optimal scalability and convergence?

Accepted Answer

Label distribution via LDP or TDP must be consistent across all P routers.. Consistent label distribution across all P (Provider) routers is essential for MPLS L3VPN scalability and convergence. LDP (Label Distribution Protocol) or TDP (Tag Distribution Protocol, Cisco proprietary predecessor) must be uniformly configured to ensure a seamless label-switched path (LSP) from ingress to egress PE. Inconsistent label distribution can cause label binding mismatches, leading to forwarding failures or suboptimal convergence during topology changes.

Answer

All PE routers must be directly connected via eBGP to exchange VPNv4 routes.

Answer

The use of BGP next-hop-self is mandatory to prevent routing blackholes in multi-area IGP environments.