JNCIP-ENT Class OF Service Practice Test 1 — 15 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

Question 11

Which TWO conditions must be met when configuring strict priority queuing for a forwarding class in Junos? (Choose two)

Accepted Answer

A shaping rate should be applied to the priority queue to prevent starvation of other queues. Option C is correct because strict priority queuing in Junos is enabled by assigning the queue a high priority level with the 'priority high' statement under the scheduler, which makes the scheduler service that queue before any others. Option B is correct because a shaping rate (or transmit-rate with a shaper) should be applied to the priority queue to cap its bandwidth and prevent it from starving lower-priority queues. Option A is incorrect because behavior aggregate classifiers are used to classify traffic into forwarding classes and are not required to be disabled for strict priority scheduling to work. Option D is incorrect because buffer sizes are not required to be zero; queues still need buffers to hold packets, and setting them to zero would be harmful. Option E is incorrect because a transmit-rate of exactly 100% is not required and would be inappropriate, since strict priority is defined by the priority setting, not by a fixed 100% transmit rate.

Answer

Behavior aggregate classifiers must be disabled on all egress interfaces

Answer

Buffer sizes must be set to zero for all priority queues

Answer

The scheduler must have a transmit-rate percentage of exactly 100%

Question 12

Which THREE components are required to fully configure a custom Class of Service scheme on an MX Series router? (Choose three)

Accepted Answer

schedulers. On an MX Series router, a complete custom Class of Service (CoS) scheme requires three core building blocks: forwarding-classes (option C), which map internal queue numbers to named forwarding classes that traffic can be assigned to; classifiers (option D), which inspect incoming packet headers (e.g., IP DSCP or 802.1p bits) and assign packets to those forwarding classes; and schedulers (option A), which define the transmit rate, buffer, and drop behavior applied to each forwarding class queue. Together these components let you classify traffic, place it into the correct forwarding class, and control how each class is serviced on egress. Option B (dynamic-profiles) is not required — it is an optional Junos feature for subscriber-based dynamic CoS configuration, not a mandatory component of a static custom CoS scheme. Option E (bgp-routes) is unrelated to CoS; BGP routing does not configure classification, queuing, or scheduling behavior.

Answer

dynamic-profiles

Answer

bgp-routes

Question 13

Which TWO statements are correct regarding hierarchical scheduling (H-QoS) on Juniper MX Series routers? (Choose two)

Accepted Answer

Subscriber management frameworks often utilize hierarchical scheduler maps. Hierarchical schedulers allow multi-level bandwidth allocation and tenant sub-rate shaping.

Answer

H-QoS eliminates the need for physical interface drop profiles

Answer

H-QoS is configured exclusively under the system routing-options hierarchy

Answer

H-QoS requires disabling all hardware-based forwarding ASICs

Question 14

Which THREE types of information can be examined using the command 'show class-of-service interface' on a Junos device? (Choose three)

Accepted Answer

Active scheduler maps. The show class-of-service interface command displays assigned scheduler maps, rewrite rules, and active classifiers on the interface.

Answer

Current BGP peer states

Answer

Routing table packet forwarding counts

Question 15

You are configuring a multi-field classifier on an SRX Series device acting as a border router. You need to classify traffic based on the source IP address and the DSCP value in the IP header. Which statement is correct about the order of operations for multi-field classifiers?

Accepted Answer

The multi-field classifier is applied as a firewall filter on the interface, and it can match on multiple fields including source IP and DSCP.. Multi-field classifiers are implemented as firewall filters applied to an interface. They can match on multiple packet header fields, including source IP address and DSCP, and then assign the packet to a forwarding class and loss priority. This provides flexible classification based on the specific requirements of the scenario.

Answer

The multi-field classifier is applied after the behavior aggregate classifier, and its results are ignored if a BA classifier is present.

Answer

The multi-field classifier uses a fixed table that maps DSCP values to forwarding classes and cannot match on source IP.

Answer

The multi-field classifier is applied before the behavior aggregate classifier, and its results override the BA classifier.