350-501 Practice Test 19 — 15 Questions

Question 1

A service provider router receives a route with a higher specific prefix length than the same prefix in the routing table. Which route will be preferred?

Accepted Answer

The more specific prefix.. C is correct because a router always prefers the most specific prefix (longest prefix length) when forwarding packets, regardless of administrative distance or metric. This is a fundamental rule of IP routing: the route with the longest subnet mask match is chosen first, as it represents the most precise path to the destination.

Answer

The route with higher administrative distance.

Answer

The route with lower metric.

Answer

The less specific prefix.

Question 2

A service provider operates a large MPLS network with hundreds of PE routers. They have deployed QoS policies to ensure real-time traffic (voice and video) receives priority. The policy uses LLQ with a strict priority queue for voice (DSCP EF) and another for video (DSCP AF41). Each priority queue has a policer to prevent starvation of other classes. Recently, a customer reports that their video calls are experiencing jitter and packet loss. The engineer examines the PE router connected to this customer. The interface is GigabitEthernet0/0/1 with the policy applied in the output direction. Show commands indicate that the video priority queue is frequently dropping packets, while the voice queue has no drops. The police for the video queue is set to 10 Mbps. The customer's contract guarantees 20 Mbps for video traffic. However, the actual video traffic is averaging 15 Mbps with bursts to 18 Mbps. The engineer notes that the video class also has a bandwidth command of 10 Mbps under the priority statement. What is the most likely cause of the video packet loss?

Accepted Answer

The police rate for the video queue is too low; increase it to at least 20 Mbps.. The video priority queue is dropping packets because the police rate (10 Mbps) is lower than the actual traffic rate (15 Mbps average, bursts to 18 Mbps). In LLQ, the priority queue uses a policer to enforce a maximum rate; traffic exceeding the police rate is dropped. The bandwidth command under priority only reserves bandwidth for the queue in the absence of congestion or for shaping purposes, but the policer is the active enforcement mechanism that causes drops. Increasing the police rate to at least 20 Mbps aligns with the customer's guaranteed rate and prevents drops.

Answer

The bandwidth command under priority is too low; increase it to 20 Mbps.

Answer

The video queue is using the wrong queue limit; increase the queue limit to accommodate bursts.

Answer

The video traffic is not being classified correctly; check the class-map match criteria.

Question 3

Which Cisco SP router platform runs IOS XR and is designed for the aggregation layer with high-density 10GE/100GE interfaces?

Accepted Answer

Cisco ASR 9000. The Cisco ASR 9000 series is optimized for the aggregation layer with dense 10GE/100GE ports and runs IOS XR.

Answer

Cisco ISR 4000

Answer

Cisco CRS

Answer

Cisco NCS 5500

Question 4

A network automation engineer needs to retrieve QoS policy statistics from a Cisco IOS XE device using RESTCONF. Which YANG module should be targeted?

Accepted Answer

Cisco-IOS-XE-QoS. The Cisco-IOS-XE-QoS YANG module is the native Cisco module that provides the data model for QoS policy configuration and operational statistics on IOS XE devices. Since the engineer is using RESTCONF to retrieve QoS statistics from a Cisco IOS XE device, this module is the correct target because it is specifically designed for and supported on IOS XE platforms.

Answer

ietf-qos

Answer

Cisco-NX-OS-device

Answer

openconfig-qos

Question 5

An engineer is configuring QoS for voice traffic on a Cisco router. Which marking should be applied to voice packets to ensure proper end-to-end prioritization?

Accepted Answer

DSCP EF. Voice traffic requires low latency, jitter, and packet loss. DSCP EF (Expedited Forwarding, per-hop behavior value 46) is the standard marking for real-time voice payloads, ensuring strict priority queuing (PQ) across the network. RFC 3246 defines EF for this purpose, and Cisco routers use it to map voice to the priority queue.

Answer

DSCP AF41

Answer

DSCP CS3

Answer

IP Precedence 3

Question 6

Which THREE of the following are correct statements about EVPN-VXLAN in a data center fabric? (Select three.)

Accepted Answer

EVPN route type 3 is used for BUM traffic forwarding.. EVPN route type 3 (Inclusive Multicast Ethernet Tag Route) is used to advertise the VTEP addresses that participate in a given broadcast domain (EVI). This enables the underlay to forward BUM (Broadcast, Unknown unicast, Multicast) traffic by building a head-end replication list or by signaling multicast group membership, ensuring that BUM frames are delivered to all remote VTEPs in the same VXLAN segment.

Answer

VXLAN is a Layer 3 overlay that requires an IGP in the overlay.

Answer

VXLAN always requires IP multicast in the underlay for BUM traffic.

Question 7

Which NETCONF operation is used to retrieve the entire running configuration from a network device?

Accepted Answer

get-config. The NETCONF `get-config` operation is specifically designed to retrieve a configuration datastore, such as the running configuration. Unlike the `get` operation, which retrieves both configuration and state data, `get-config` targets only the configuration data, making it the precise operation for fetching the entire running configuration from a network device.

Answer

get

Answer

commit

Answer

edit-config

Question 8

In an SR network, which configuration is required to activate TI-LFA for link protection?

Accepted Answer

fast-reroute per-prefix ti-lfa under the IGP process. TI-LFA (Topology Independent Loop-Free Alternate) is activated under the IGP process using the 'fast-reroute per-prefix ti-lfa' command. This enables segment routing to compute a backup path that provides link protection without relying on the topology of the failure, ensuring 50-msec convergence.

Answer

metric delay interface configuration

Answer

label-preferred under the interface

Answer

mpls traffic-eng auto-tunnel primary

Question 9

An engineer is configuring MPLS on a Cisco router. Which label operation is performed on the ingress LSR when a packet enters the MPLS domain?

Accepted Answer

Push a new label. The ingress LSR pushes a new label onto the stack, encapsulating the original IP packet with an MPLS header.

Answer

Pop the top label

Answer

No label operation

Answer

Swap the top label

Question 10

Which IS-IS metric type is required for traffic engineering and segment routing?

Accepted Answer

Wide metrics. IS-IS wide metrics (TLV 22 and 135) use 24-bit or 32-bit values, allowing higher link costs needed for TE. Narrow metrics are limited to 6 bits.

Answer

Narrow metrics

Answer

Extended metrics

Answer

Default metrics

Question 11

Which BGP attribute is used to influence inbound traffic to an AS by indicating the preferred path into the AS?

Accepted Answer

MED. The MED (Multi-Exit Discriminator) is used to influence inbound traffic from neighboring ASes. It is advertised to eBGP peers and is compared when multiple paths to the same prefix exist from the same neighboring AS.

Answer

AS_PATH

Answer

LOCAL_PREF

Answer

Weight

Question 12

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

Accepted Answer

Shaping buffers excess traffic, while policing drops or re-marks it.. Policing drops or re-marks excess traffic; shaping buffers excess and smooths output.

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 13

A service provider is deploying a point-to-point Layer 2 VPN across an MPLS network using Ethernet over MPLS (EoMPLS) with Martini encapsulation. The customer requires transparent transport of VLAN tags (Q-in-Q) between two sites. The provider configures the attachment circuits on the PE routers as VLAN subinterfaces with dot1q encapsulation. After configuration, the customer reports that only untagged frames pass through the pseudowire; double-tagged frames are dropped at the egress PE. Which action resolves the issue?

Accepted Answer

Change the encapsulation on the PE subinterfaces to dot1q second-dot1q and enable the preservation of the outer VLAN tag at the ingress PE. EoMPLS with Martini encapsulation (RFC 4448) supports Q-in-Q transparent transport only when the ingress PE is configured to preserve the outer VLAN tag. Using 'dot1q second-dot1q' encapsulation on the subinterface tells the PE to treat the outer tag as part of the payload and not strip it, allowing both tags to be carried across the pseudowire. Without this, the default dot1q encapsulation strips the outer tag, causing double-tagged frames to be dropped at the egress PE.

Answer

Replace the attachment circuit with a port-mode Layer 2 interface and disable VLAN tagging on the PE

Answer

Configure the pseudowire to use the 'tag-imposition' keyword to allow double tagging

Answer

Configure the PE routers to use VLAN translation to map both tags to a single tag before encapsulation

Question 14

Which THREE are correct statements about IOS XR process separation? (Choose three.)

Accepted Answer

Processes can be restarted independently without affecting others. IOS XR runs each protocol as a separate process, providing fault isolation and independent restart.

Answer

A failure in one process can crash the entire system

Answer

All processes share a single memory space

Question 15

You are responsible for network assurance for a Tier-1 ISP that has deployed model-driven telemetry using gNMI with ON_CHANGE subscriptions on all core routers. Recently, the NMS team reported that some BGP route flaps are not being captured in the telemetry data, even though the routers' syslogs show the flaps occurred. The telemetry subscription is for the path '/bgp/neighbors/neighbor/state/messages/received'. The NMS is using a gNMI collector that supports both ON_CHANGE and SAMPLE subscriptions. You suspect the issue is with the subscription configuration. Upon reviewing the router configuration, you see that the telemetry subscription uses the SAMPLE mode instead of ON_CHANGE. What is the most appropriate action to ensure all BGP route flap events are captured?

Accepted Answer

Modify the subscription to use ON_CHANGE mode for the BGP neighbor paths.. The gNMI ON_CHANGE subscription mode is designed to stream telemetry updates only when the value of a subscribed path changes. Since the NMS is missing BGP flap events, the subscription must be using SAMPLE mode, which periodically polls the state and can miss transient events between sampling intervals. Changing the subscription to ON_CHANGE ensures that every state transition (e.g., BGP session up/down) is immediately pushed to the collector, capturing all flaps.

Answer

Configure the router to send syslogs to the NMS and parse them for BGP flaps.

Answer

Add a second subscription with ON_CHANGE for the same paths to ensure redundancy.

Answer

Change the subscription to SAMPLE with a 1-second interval to capture flaps more frequently.