JNCIP-ENT Class OF Service — 10 Questions

Question 1

An administrator needs to implement a traffic conditioning profile on a Juniper MX Series router to limit traffic to a specific burst size and drop packets exceeding the rate. Which policing action parameter is required to ensure that exceeding traffic is dropped immediately without coloring?

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

Accepted Answer

discard. A policer in Junos uses policer action statements like loss-priority or discard. To drop non-compliant traffic immediately, the action discard is configured.

Answer

forwarding-class

Answer

transmit

Answer

mark-action

Question 2

An administrator is troubleshooting a multi-field classifier configuration on an MX router. The classifier is failing to match traffic based on Layer 4 ports. What is the most likely cause?

Accepted Answer

Layer 4 headers are encrypted by IPsec and cannot be inspected by standard classifiers. Multi-field classifiers in Junos are implemented using firewall filters with then forwarding-class actions, requiring correct term ordering and matching fields.

Answer

Layer 4 classification requires an explicit forwarding-class map under system services

Answer

Multi-field classifiers do not support TCP ports in Junos

Answer

Layer 4 matching is only supported on ingress CoS rewrite rules

Question 3

You are configuring a Junos device and need to classify incoming traffic based on the IP precedence bits within the IPv3 header. Which classifier type should you select under the class-of-service configuration hierarchy?

Accepted Answer

ip-precedence. IP precedence uses the three most significant bits of the IPv3 Type of Service (ToS) byte. In Junos, the correct classifier type for this is ip-precedence.

Answer

ieee-802.1

Answer

exp

Answer

dscp

Question 4

When configuring a hierarchical policer on a Juniper MX Series router, what is the significance of the logical-interface-policer setting?

Accepted Answer

It shares a single policer bucket across all forwarding classes on the logical interface. A logical-interface-policer applies a single policer instance shared across all queues or forwarding classes on that specific logical interface.

Answer

It separates policing actions strictly for Layer 2 control frames

Answer

It disables hardware-based policing and falls back to RE software rate-limiting

Answer

It applies the policer globally across all physical interfaces on the Routing Engine

Question 5

An administrator configures a scheduler map with a transmit-rate of percent 20 for a queue, but the total sum of transmit-rates in the map equals 110%. How does Junos handle this configuration?

Accepted Answer

The commit fails because the sum of percentage transmit-rates exceeds 100%. In Junos, when configuring a scheduler map with transmit-rate as a percentage, the sum of all transmit-rate percentages across all queues in that map must not exceed 100%. If the total exceeds 100%, the commit operation fails with an error indicating that the sum of transmit rates exceeds 100%. This is a strict validation check performed by the Junos CLI during commit, ensuring that the scheduler map does not over-allocate bandwidth. Therefore, option A is correct.

Answer

Traffic exceeding 100% is dropped by the Routing Engine

Answer

Junos normalizes the percentages proportionally during commit time

Answer

The excess 10% is automatically assigned to the best-effort queue

Question 6

Which command allows you to view the configured drop-profile statistics and monitor packet drop counts on an MX Series router?

Accepted Answer

show class-of-service drop-profile. The show class-of-service drop-profile command displays drop-profile utilization and drop statistics.

Answer

show firewall log

Answer

show interfaces drop-rate

Answer

show system drop-stats

Question 7

What is the default number of forwarding classes available on Juniper MX Series routers equipped with Modular Port Concentrators (MPCs)?

Accepted Answer

64. Junos supports up to 64 forwarding classes on modern MPC-based hardware platforms, though default configurations typically use a subset.

Answer

4

Answer

8

Answer

16

Question 8

You are configuring a policer and want to specify the rate in terms of bits per second. Which keyword is used to define the bandwidth limit in the policer configuration?

Accepted Answer

bandwidth-limit. Policer bandwidth limits in Junos are defined using the bandwidth-limit or burst-size-limit keywords.

Answer

peak-rate

Answer

rate-limit

Answer

transmit-rate

Question 9

Which component of a scheduler configuration determines how memory resources are allocated among different queues?

Accepted Answer

buffer-size. The buffer-size parameter determines memory buffer allocation for each queue in a scheduler configuration.

Answer

drop-profile-map

Answer

transmit-rate

Answer

priority

Question 10

You are configuring traffic shaping on an egress interface and need to ensure that the shaper accounts for Layer 2 framing overhead (such as Ethernet headers and preambles). Which configuration statement achieves this?

Accepted Answer

set class-of-service traffic-control-profiles <profile> shaping-rate ... layer-2-overhead. The explicit specification of accounting for layer 2 overhead in Junos CoS shaping is done via the explicit-tracking or layer-2-overhead options under the traffic-control-profile or scheduler.

Answer

set routing-options forwarding-table l2-accounting

Answer

set firewall family inet filter <filter> overhead-accounting

Answer

set class-of-service interfaces <interface> encapsulation-overhead