350-501 Practice Test 4 — 25 Questions

Question 1

An SP engineer configures a QoS policy on an IOS XR router to re-mark DSCP from AF11 to AF22 for traffic matching a specific ACL. The policy compiles successfully but traffic is not re-marked. What is a likely reason?

Accepted Answer

The interface does not have the 'qos' feature enabled, or the policy-map is not attached.. Option C is correct because on IOS XR routers, QoS policies require explicit feature enablement via the 'qos' command under the interface configuration, and the policy-map must be attached in the correct direction. Without the 'qos' feature enabled, the router will compile the policy but silently ignore it, resulting in no re-marking of DSCP from AF11 to AF22.

Answer

The ACL cannot match on DSCP values.

Answer

The ACL is applied to the wrong interface.

Answer

The policy is applied in the output direction; marking can only be done on ingress.

Question 2

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 3

A service provider is experiencing suboptimal routing due to BGP route reflection. To improve path selection while maintaining IBGP scalability, which feature should be implemented?

Accepted Answer

BGP optimal route reflection (ORR). BGP optimal route reflection (ORR) improves path selection by allowing the route reflector to calculate the best path based on the IGP metric to the client's location, rather than using its own BGP table. This overcomes the suboptimal routing caused by standard route reflection, where the RR's best path may not be optimal for all clients, while still maintaining IBGP scalability by avoiding a full mesh.

Answer

BGP deterministic med

Answer

BGP next-hop-self

Answer

BGP add-path

Question 4

An SP is using NETCONF with YANG to automate VRF provisioning. The engineer notices that the NETCONF session is established but configuration changes are not applied. Which issue is most likely?

Accepted Answer

The NETCONF capability :candidate is not advertised. NETCONF uses datastores to manage configuration. The `:candidate` capability allows changes to be made to a candidate configuration before committing them. If this capability is not advertised, the device defaults to the `:writable-running` capability, which requires changes to be applied directly to the running datastore. Since the engineer is likely using a candidate-based workflow (e.g., `edit-config` with target `candidate`), the session establishes but changes are silently ignored or rejected because the device does not support a separate candidate datastore.

Answer

The YANG model does not support the target configuration datastore

Answer

The device does not support :url capability

Answer

The user does not have write access to the candidate datastore

Question 5

Which TWO are essential components for deploying EVPN in a service provider network?

Accepted Answer

Overlay tunnel encapsulation such as VXLAN or MPLS. A is correct because EVPN requires an overlay tunnel encapsulation to transport Layer 2 frames across the IP/MPLS underlay. VXLAN (RFC 7348) and MPLS (RFC 7432) are the two primary encapsulations used to carry Ethernet frames over the overlay, enabling MAC address learning and forwarding in the EVPN control plane.

Answer

OSPF as the underlay routing protocol

Answer

PIM-SM for multicast replication

Answer

RSVP-TE for path computation

Question 6

A service provider is implementing MPLS L3VPN for a customer. The customer requires that routes from two different VPNs be imported into a single VRF. Which feature should be used?

Accepted Answer

Route Target (RT) import/export. Route Target (RT) import/export is the correct feature because it controls which routes from which VPNs are imported into a given VRF. By configuring multiple RT import statements on a single VRF, the provider can selectively import routes from two different VPNs, enabling inter-VPN route sharing without merging the VPNs themselves.

Answer

Route Reflector

Answer

Route Distinguisher (RD)

Answer

BGP extended community

Question 7

A service provider is implementing Segment Routing (SR) with MPLS. Which three statements are true regarding SR-MPLS? (Choose three.)

Accepted Answer

SR-MPLS does not require LDP or RSVP-TE. B is correct because SR-MPLS uses the MPLS data plane but replaces the control plane protocols LDP and RSVP-TE with IGP extensions (IS-IS or OSPF) to distribute segment information. This eliminates the need for these traditional label distribution protocols, simplifying network operations and reducing protocol overhead.

Answer

SR-MPLS supports traffic engineering only with a central controller

Answer

Adjacency SIDs are advertised via BGP-LS

Question 8

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 9

Refer to the exhibit. A PE router configuration for VRF CUST1 is shown. What is the most likely result when a CE sends a route with RT 100:100?

Accepted Answer

The route is received but not imported into VRF. The VRF CUST1 configuration does not include a route-target import statement for RT 100:100. Without a matching import RT, the PE router will receive the route from the CE but will not import it into the VRF. The route is received (BGP update is accepted) but not installed in the VRF routing table, making option D correct.

Answer

The route causes a BGP session reset

Answer

The route is imported and installed in VRF

Answer

The route is imported but not advertised to other CEs

Question 10

A network engineer notices that voice traffic is being dropped during congestion. The traffic is marked with DSCP EF. After reviewing the QoS policy, it is discovered that the voice traffic is not being placed into a priority queue. Which configuration change would ensure voice traffic receives priority treatment?

Accepted Answer

Add the 'priority' command under the voice class in the policy map. DSCP EF (Expedited Forwarding, per RFC 3246) requires strict priority queuing to guarantee low latency and jitter for voice traffic. The 'priority' command under the voice class in a policy map places the traffic into a strict priority queue (LLQ), ensuring it is serviced before any other queue during congestion. Without this command, the voice traffic is treated as a regular class, subject to bandwidth constraints and potential drops.

Answer

Increase the queue limit to 1000 packets

Answer

Increase the bandwidth percentage for the voice class

Answer

Enable WRED on the voice class

Question 11

Refer to the exhibit. Based on the exhibit, what is the most likely reason for no label bindings?

Accepted Answer

The remote peer has label filtering applied. Option D is correct because the exhibit shows that the local router has received label bindings from the remote peer (as seen in the 'show mpls ldp bindings' output), but the local router has not installed any labels in its forwarding table. This indicates that the remote peer is advertising labels, but the local router is filtering those labels from being used, typically via an inbound label filtering policy. Label filtering can be applied using 'mpls ldp neighbor [neighbor-id] label-filter' or 'mpls ldp label-filter' to accept or reject specific label bindings, which matches the scenario where bindings are received but not used.

Answer

The local router has disabled label advertisements

Answer

The IGP routes are not present in the routing table

Answer

The LDP session is not fully established

Question 12

In a multicast environment, a PE router is not receiving multicast traffic from a source behind a CE. The PIM neighbors are established. The RP is reachable. What is the most likely issue?

Accepted Answer

The PE does not have the multicast VRF enabled. The most likely issue is that the PE router does not have the multicast VRF enabled. In a multicast VPN (MVPN) environment, even if PIM neighbors are established and the RP is reachable, the PE must have multicast routing explicitly enabled within the VRF using the 'ip multicast-routing vrf <name>' command. Without this, the PE will not process multicast traffic for that VRF, causing it to drop or ignore multicast packets from the source behind the CE.

Answer

The CE is not sending IGMP joins

Answer

The source address is not in the VRF

Answer

The RP is not configured in the VRF

Question 13

An OSPF network uses point-to-point links. The engineer notices that LSAs are being flooded every 30 minutes even when no topology changes occur. What is the most likely reason?

Accepted Answer

The LSA refresh interval has expired.. In OSPF, LSAs have a default refresh interval of 30 minutes (1800 seconds). When this timer expires, the router that originated the LSA re-floods it to maintain database synchronization, even if no topology changes have occurred. This is normal OSPF behavior defined in RFC 2328, and it explains why LSAs are flooded every 30 minutes.

Answer

The routers are using LSU packets incorrectly.

Answer

There is a flapping interface on the network.

Answer

The dead timer is set too low.

Question 14

A service provider is troubleshooting an L2VPN where a CE is unable to ping the remote CE. The PE-CE interfaces are up, and the pseudowire status shows 'up'. Which two actions should be taken to further isolate the issue? (Choose two.)

Accepted Answer

Verify the VC ID match on both PEs. Option D is correct because the VC ID (Virtual Circuit ID) must match on both PEs for the pseudowire to be established correctly. If the VC IDs are mismatched, the pseudowire status may show as 'up' due to local signaling, but traffic will not be forwarded between the CEs because the pseudowire endpoints are not logically connected. Verifying the VC ID ensures that the L2VPN circuit is properly configured end-to-end.

Answer

Check the MAC address table on the CE

Answer

Check the LDP session between PEs

Answer

Verify the VFI configuration on the PE

Question 15

An SP has configured MPLS TE tunnels for traffic engineering. To verify the status of the TE tunnels, which command provides the most relevant information?

Accepted Answer

show mpls traffic-eng tunnels brief. The 'show mpls traffic-eng tunnels brief' command directly displays the status, state (up/down), and key parameters (e.g., bandwidth, path) of all configured MPLS TE tunnels, making it the most relevant command for verifying TE tunnel status. It provides a concise view of tunnel endpoints, admin/operational states, and signaled bandwidth, which is essential for traffic engineering verification.

Answer

show mpls forwarding-table

Answer

show mpls ldp tunnels

Answer

show ip rsvp reservation

Question 16

A network engineer is designing a new MPLS core. Which three of the following are recommended best practices for MPLS LDP configuration? (Choose three.)

Accepted Answer

Enable LDP authentication using MD5. C is correct because enabling LDP authentication using MD5 protects the LDP session from spoofing and tampering by verifying the integrity of TCP segments exchanged between LDP peers. This is a recommended security best practice in MPLS networks to prevent unauthorized label distribution and route hijacking.

Answer

Use explicit null label for BGP prefixes

Answer

Set the LDP session holdtime to 180 seconds

Question 17

In a carrier network using VRF-lite for customer isolation, which issue arises if route-target values are not correctly configured?

Accepted Answer

Customer routes leak into other VRFs.. In VRF-lite, route-target (RT) values control the import and export of routes between VRFs. If RTs are misconfigured, a VRF may import routes intended for another VRF, causing customer routes to leak across VRFs. This violates isolation because the VRF table incorrectly accepts routes based on mismatched RT import statements.

Answer

Customer routes are not installed in the global table.

Answer

BGP sessions between PEs flap.

Answer

The PE-CE routing protocol fails.

Question 18

Refer to the exhibit. An engineer has configured an SR-TE policy. What is required for this policy to be used for traffic steering?

Accepted Answer

BGP with color extended community. Option C is correct because an SR-TE policy uses a color extended community to identify the policy's color and its associated endpoint. BGP distributes these color extended communities, enabling headend routers to match traffic to the correct SR-TE policy for steering. Without BGP carrying the color extended community, the policy cannot be dynamically selected for traffic engineering.

Answer

Static routing

Answer

IGP with segment routing

Answer

OSPF with opaque LSA

Question 19

When configuring EVPN VPWS, which TWO parameters must match between the two endpoints of the pseudowire?

Accepted Answer

EVI (Ethernet VPN Instance). In EVPN VPWS (Virtual Private Wire Service), the EVI (Ethernet VPN Instance) must match between endpoints because it uniquely identifies the EVPN instance and is used to derive the Route Distinguisher (RD) and control-plane context for the pseudowire. The ESI (Ethernet Segment Identifier) must also match because it identifies the local Ethernet segment and is used for split-horizon filtering and DF election; mismatched ESI values will cause the pseudowire to fail to come up.

Answer

Route-target

Answer

VLAN ID of the attachment circuit

Answer

IMET group address

Question 20

A customer is using a Cisco ASR 9000 router with hierarchical QoS (HQoS) on a subscriber interface. The parent policy sets a shape rate of 10 Mbps, but the observed traffic rate is only 8 Mbps. What is a common misconfiguration that would cause this?

Accepted Answer

The child policy includes a police command that is limiting traffic below the parent shaper rate. In hierarchical QoS (HQoS) on a Cisco ASR 9000, the parent policy shapes traffic to a specified rate, but if the child policy includes a police command, that policer can independently drop or mark down traffic before it reaches the parent shaper. This causes the observed traffic rate to be lower than the parent shape rate, as the child policer is the actual bottleneck. The correct answer is A because the police command in the child policy is limiting traffic below the 10 Mbps parent shaper, resulting in only 8 Mbps observed.

Answer

The child policy uses 'bandwidth remaining' instead of 'bandwidth'

Answer

The child policy includes a bandwidth command that exceeds the parent shaper rate

Answer

The parent shaper uses 'shape peak' instead of 'shape average'