JNCIP-ENT Class OF Service Practice Test 3 — 15 Questions

Question 1

You want to map three loss priorities (low, medium-low, high) to different drop profiles within a specific forwarding class. Which statement should you use inside the scheduler configuration?

Accepted Answer

drop-profile-map. In Junos scheduler configurations, drop-profile-map associates a loss priority and forwarding class with a specific drop profile.

Answer

classifier-map

Answer

loss-priority-mapping

Answer

queue-drop-profile

Question 2

Which TWO parameters can be configured within a Junos scheduler definition? (Choose two)

Accepted Answer

transmit-rate. Schedulers include parameters such as transmit-rate, buffer-size, priority, and drop-profile-map.

Answer

rewrite-rule

Answer

bandwidth-limit

Answer

policer-action

Question 3

In Junos CoS architecture, what role does a forwarding class play?

Accepted Answer

It represents an internal queue abstraction used to group and process packets. Forwarding classes act as internal labels used by the router to group traffic into specific queues for scheduling and drop treatment.

Answer

It specifies the egress interface physical speed

Answer

It provides static IP routing table entries

Answer

It defines the physical queue index directly on the ASIC

Question 4

Which THREE types of classifiers are natively supported in Junos Class of Service? (Choose three)

Accepted Answer

exp. Junos CoS natively supports three fixed classifier types: exp, dscp, and ieee-802.1. Option A (exp) is correct because the MPLS EXP classifier maps the 3-bit EXP field in the MPLS shim header to forwarding classes and loss priorities. Option B (dscp) is correct because the DSCP classifier examines the 6-bit Differentiated Services Code Point in the IP ToS byte for IP traffic. Option C (ieee-802.1) is correct because the IEEE 802.1 classifier inspects the 3-bit User Priority field in the 802.1Q VLAN tag for Layer 2 traffic. Options D (tcp-port) and E (mac-address) are not native Junos CoS classifier types; Junos classifiers operate on CoS marking fields such as EXP, DSCP, and 802.1p, not on TCP port numbers or MAC addresses.

Answer

tcp-port

Answer

mac-address

Question 5

Which TWO statements are correct regarding the behavior of policers in Junos? (Choose two)

Accepted Answer

Policers can mark the loss priority of exceeding packets. Policers can drop traffic or mark loss priority, and they operate based on token bucket algorithms.

Answer

Policers buffer exceeding packets in temporal memory queues until transmission capacity opens

Answer

Policers are always applied to egress interfaces only

Answer

Policers guarantee a minimum bandwidth allocation for best-effort traffic

Question 6

You are troubleshooting a scenario where multi-field classifiers and behavior aggregate classifiers are both configured on the same ingress interface. In what order does Junos process classification?

Accepted Answer

Behavior aggregate classification is evaluated first, and multi-field classification can override the result. Junos processes Behavior Aggregate (BA) classification first, followed by Multi-Field (MF) classification which can override the BA result.

Answer

Junos rejects configurations where both BA and MF classifiers are applied to the same interface

Answer

Both classifiers are executed simultaneously in hardware without precedence

Answer

Multi-field classification is evaluated first, followed by behavior aggregate classification

Question 7

Which THREE methods are valid for marking packet headers using CoS rewrite rules in Junos? (Choose three)

Accepted Answer

exp. In Junos CoS rewrite rules, the valid header fields you can rewrite are the EXP bits (for MPLS), IEEE 802.1p (for Layer 2 CoS), and DSCP (for IP ToS). Option A (exp) is correct because MPLS EXP bits are rewritten via the exp rewrite rule. Option B (ieee-802.1) is correct because 802.1p priority bits in VLAN tags are rewritten via the ieee-802.1 rewrite rule. Option C (dscp) is correct because IP DSCP values are rewritten via the dscp rewrite rule. Options D (vlan-id) and E (mpls-ttl) are not valid rewrite-rule match/rewrite fields; vlan-id is a VLAN identifier, not a CoS marking, and MPLS TTL is a forwarding/hop-limit field, not a CoS rewrite target.

Answer

vlan-id

Answer

mpls-ttl

Question 8

Which THREE actions can be executed by a firewall filter policer when traffic exceeds the specified rate? (Choose three)

Accepted Answer

discard. In Junos firewall filter policers, the three valid actions that can be configured when traffic exceeds the specified rate are discard, loss-priority high, and forward. Option A (discard) is correct because the policer can simply drop out-of-profile packets, which is the most common bandwidth-limiting behavior. Option B (loss-priority high) is correct because the policer can mark excess packets with a high loss priority so downstream congestion-management (RED/WRED) drops them preferentially instead of dropping them immediately. Option D (forward) is correct because the policer can pass out-of-profile packets through while optionally setting a loss priority, allowing later devices or schedulers to handle them. Option C (reroute-lsp) is not a policer action; it is an MPLS routing action used in routing policies or forwarding-adjacency contexts, not in a policer's then statement. Option E (queue-switch) is not a valid policer action either; queue selection is handled by forwarding classes and schedulers, not by policers.

Answer

reroute-lsp

Answer

queue-switch

Question 9

Which TWO statements describe the characteristics of Random Early Detection (RED) and drop profiles in Junos? (Choose two)

Accepted Answer

Drop profile curves plot drop probability against queue buffer fill level. Drop profiles define drop probability against fill level, helping prevent TCP global synchronization.

Answer

Drop profiles are configured under the forwarding-classes hierarchy

Answer

Drop profiles drop 100% of packets immediately once the queue fill level reaches the start point

Answer

Drop profiles operate exclusively on Layer 2 control frames

Question 10

Which TWO statements are true regarding traffic shapers versus policers in Junos? (Choose two)

Accepted Answer

Shapers are typically implemented on egress interfaces. Shapers buffer excess traffic to smooth out bursts, whereas policers drop or mark exceeding traffic immediately.

Answer

Policers are primarily configured on egress interfaces for shaping purposes

Answer

Policers buffer exceeding traffic in dedicated memory queues

Answer

Shapers operate without drop profiles or buffer allocation

Question 11

An enterprise WAN edge router running Junos OS has a single 1 Gbps uplink. The design requires that when total egress congestion occurs, the queue carrying business-critical database replication traffic must be guaranteed a minimum of 400 Mbps, while the queue carrying guest internet traffic must never consume more than 200 Mbps even if bandwidth is idle. Which CoS configuration accomplishes this requirement?

Accepted Answer

Apply a transmit-rate of 400m to the critical queue and a shaping-rate of 200m to the guest queue in the scheduler.. Guaranteeing a minimum and enforcing a maximum are distinct scheduler behaviors. A transmit-rate provides the guaranteed minimum share during congestion, whereas a shaping-rate imposes a hard ceiling on how much a queue can transmit even when bandwidth is available. The critical queue needs the guarantee and the guest queue needs the cap, so pairing transmit-rate with shaping-rate matches the design intent.

Answer

Apply a transmit-rate of 400m to the critical queue and a transmit-rate of 200m to the guest queue in the scheduler.

Answer

Apply a shaping-rate of 400m to the critical queue and a transmit-rate of 200m to the guest queue in the scheduler.

Answer

Apply a transmit-rate of 400m with exact to the critical queue and a transmit-rate of 200m with exact to the guest queue in the scheduler.

Question 12

You are configuring Class of Service on an MX Series router. You want to ensure that the best-effort forwarding class receives at least 10 Mbps of bandwidth during congestion on a 1 Gbps interface, but you also want to allow it to use additional bandwidth if other queues are idle. Which scheduler configuration should you apply?

Accepted Answer

transmit-rate 10m;. The scheduler transmit-rate statement with a specific value like 10m sets a guaranteed minimum bandwidth for the queue. When other queues are not using their allocated bandwidth, the scheduler allows this queue to exceed its minimum, up to the interface or shaping rate. This provides both a guaranteed floor and the ability to burst, which matches the scenario requirements.

Answer

transmit-rate percent 1;

Answer

transmit-rate remainder;

Answer

shaping-rate 10m;

Question 13

You are deploying a Junos EX Series switch in a campus network. Voice packets arrive untagged from IP phones on access ports, while a trunk uplink carries traffic already marked with DSCP values from the core. You need to ensure that all ingress traffic on the uplink is classified into forwarding classes based solely on the existing DSCP bits without inspecting Layer 3 or Layer 4 headers. Which classifier type should you apply to the uplink interface?

Accepted Answer

Behavior aggregate classifier. Because the incoming packets on the uplink already carry DSCP markings from the core and the goal is to classify them without deeper header inspection, a behavior aggregate classifier is the correct mechanism. BA classifiers map a single CoS field such as DSCP directly to a forwarding class and loss priority, providing efficient, marking-based classification at ingress.

Answer

Fixed classifier

Answer

Multifield classifier

Answer

EXP classifier

Question 14

You are deploying a Junos EX Series switch in a campus network. Voice traffic arrives untagged and must be placed into the expedited-forwarding forwarding class based solely on the Differentiated Services Code Point (DSCP) value carried in the IP header. No firewall filter is allowed on the ingress interface. Which classifier type should you apply to the interface?

Accepted Answer

A behavior aggregate (BA) classifier applied to the ingress interface. A behavior aggregate classifier examines a single CoS field, such as the DSCP bits, and assigns the packet to a forwarding class and loss priority. Since the requirement is to classify untagged voice traffic purely by DSCP with no firewall filter, a BA classifier bound to the ingress interface is the correct and simplest solution.

Answer

A multi-field (MF) classifier applied to the ingress interface

Answer

An egress rewrite rule applied to the interface

Answer

A fixed classifier applied to the ingress interface

Question 15

A network engineer notices that on a Junos EX Series switch, the voice queue is configured with strict-high priority, but during periods of congestion, data traffic is being dropped while voice traffic is unaffected. The engineer wants to ensure that voice traffic is not only prioritized but also limited so it cannot consume all interface bandwidth. Which scheduler property should be added to the voice queue to cap its maximum transmission rate?

Accepted Answer

shaping-rate. A strict-high priority queue can consume all available bandwidth during congestion, starving lower-priority queues. To prevent this while preserving priority servicing, the shaping-rate property must be configured on the voice queue to enforce a maximum transmission rate. This caps the voice queue's consumption and protects other traffic.

Answer

transmit-rate

Answer

buffer-size

Answer

excess-rate