350-501 Practice Test 6 — 10 Questions

Question 1

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'

Question 2

In an MPLS network, which field in the MPLS label header is used to carry QoS information between LSRs?

Accepted Answer

EXP bits. In MPLS, the EXP (Experimental) bits, also known as the Traffic Class (TC) field per RFC 5462, are 3 bits in the MPLS label header used to carry Quality of Service (QoS) information between Label Switch Routers (LSRs). These bits allow LSRs to apply per-hop behaviors (PHBs) such as queuing and scheduling based on the packet's QoS class, enabling differentiated services across the MPLS network.

Answer

ToS

Answer

IP Precedence

Answer

DSCP

Question 3

Which congestion avoidance technique drops packets probabilistically before the queue becomes full?

Accepted Answer

WRED. WRED (Weighted Random Early Detection) is a congestion avoidance mechanism that monitors the average queue depth and, when it exceeds a configured threshold, begins dropping packets probabilistically before the queue becomes completely full. This proactive dropping signals TCP senders to reduce their transmission rates, thereby preventing tail drop and global synchronization.

Answer

FIFO

Answer

Priority Queuing

Answer

Custom Queuing

Question 4

Which TWO conditions cause a router to drop packets when a police action is configured?

Accepted Answer

exceed action is drop. When a police action is configured, the router uses a token bucket model to meter traffic. If traffic exceeds the committed information rate (CIR) and burst size, it falls into the 'exceed' or 'violate' category depending on the configured conform and exceed burst parameters. The 'drop' action for exceed or violate conditions explicitly instructs the router to discard those packets, enforcing traffic shaping or policing at the hardware or software level.

Answer

conform action is drop

Answer

no bandwidth is reserved

Answer

queue is full

Question 5

Which THREE QoS mechanisms can be used for traffic policing?

Accepted Answer

dual-rate three-color. Traffic policing uses token bucket mechanisms to measure and enforce traffic rates. Dual-rate three-color (RFC 2698) uses two token buckets (CIR/PIR) to mark packets as green, yellow, or red, allowing separate policing of committed and peak rates. Single-rate two-color (RFC 2697) uses one token bucket to mark packets as either conforming (green) or exceeding (red). Both are standard policing implementations.

Answer

WRED

Answer

shaping

Question 6

A customer has a 100 Mbps access link and wants to limit traffic to 95 Mbps with burst allowance up to 100 Mbps. Which QoS action should be applied on the egress interface?

Accepted Answer

police. Police is the correct QoS action because it allows you to enforce a maximum traffic rate (95 Mbps) while permitting bursts up to 100 Mbps, dropping or remarking excess traffic. Unlike shaping, policing does not buffer traffic, so it can enforce a hard limit on egress without introducing delay, which matches the requirement to limit traffic with a burst allowance.

Answer

shape

Answer

priority

Answer

bandwidth

Question 7

An enterprise uses IPsec VPN to connect branch offices. They apply QoS policies on the tunnel interface but notice that original DSCP markings are not preserved after encryption. Which feature should be enabled to maintain end-to-end QoS?

Accepted Answer

QoS pre-classify. When IPsec encrypts a packet, the original IP header (including DSCP markings) is hidden inside the tunnel payload. The tunnel interface then applies a new outer IP header, and QoS policies applied to the tunnel interface classify based on the outer header's DSCP, which defaults to 0. Enabling 'qos pre-classify' on the crypto map or tunnel interface copies the original DSCP value to the outer IP header before encryption, preserving end-to-end QoS markings across the IPsec tunnel.

Answer

AutoQoS

Answer

MPLS TE

Answer

NBAR

Question 8

A large enterprise recently implemented centralized QoS policies using Cisco DNA Center. The policies are pushed via RESTCONF to the branch routers. After the deployment, the branch office reports that critical business applications (like ERP) are being delayed. The network team verifies that the QoS policy is applied correctly on the WAN interface (Serial0/0/0) with a shape of 10 Mbps. The policy-map has a class for 'critical-data' with bandwidth 5 Mbps and another class for 'transactional-data' with bandwidth 3 Mbps. The remaining traffic is in class-default with fair-queue. The branch router's CPU utilization is normal. The interface output shows that the queue for critical-data is rarely full, but packets are experiencing high latency. The engineer pings from the branch server to the central site and sees 200 ms RTT normally, but up to 500 ms during peak hours. What is the most likely cause of the high latency for critical-data?

Accepted Answer

The shape rate is too low; increase it to match the access link speed (e.g., 20 Mbps).. The correct answer is A because the shape rate of 10 Mbps is the bottleneck. Even though the critical-data class has a bandwidth guarantee of 5 Mbps, the overall interface is shaped to 10 Mbps. During peak hours, when the sum of all traffic (critical, transactional, and default) exceeds 10 Mbps, packets are queued at the shaper. This queueing introduces additional delay (up to 500 ms) for all classes, including critical-data, because the shaper enforces a single token bucket for the entire interface. Increasing the shape rate to match the actual access link speed (e.g., 20 Mbps) would reduce the queuing delay by allowing more traffic to be transmitted immediately.

Answer

The critical-data class needs a priority command to reduce latency.

Answer

The queue-limit for critical-data is too high; reduce it to force early drops.

Answer

The bandwidth command in critical-data should be increased above 5 Mbps.

Question 9

A service provider is configuring BGP community propagation in an MPLS VPN network. Which two actions are necessary to ensure that communities are passed from CE to remote PE?

Accepted Answer

Configure send-community on the CE-to-PE BGP session. B is correct because the `send-community` command must be configured on the CE-to-PE BGP session to allow standard BGP communities (e.g., NO_EXPORT) to be propagated from the CE router into the MPLS VPN network. Without this, the PE router will strip communities from incoming BGP updates, preventing them from reaching the remote PE.

Answer

Configure no bgp default community-mode

Answer

Configure vrf forwarding with route-target both

Answer

Configure route-map to filter communities

Question 10

A network operator uses gRPC Network Management Interface (gNMI) to collect telemetry data from routers. They notice that some updates are missing. Which gNMI mode should be used to ensure that all state changes are captured?

Accepted Answer

ON_CHANGE. ON_CHANGE mode in gNMI ensures that the target device sends a telemetry update immediately whenever a state change occurs, guaranteeing that no updates are missed. This is in contrast to SAMPLE mode, which only sends periodic snapshots and can miss transient changes between intervals. Therefore, to capture all state changes, ON_CHANGE is the correct subscription mode.

Answer

TARGET_DEFINED

Answer

POLL

Answer

SAMPLE