JNCIA Class of Service

Question 1

What is Class of Service (CoS) in the context of Junos networking?

Accepted Answer

A set of mechanisms for differentiating network traffic and providing varying service levels (priority, bandwidth, delay) to different traffic types

Answer

Class of Service (CoS) in Junos enables network operators to prioritize and manage traffic based on its type or application, ensuring critical applications receive appropriate bandwidth and low latency.

Question 2

In Junos CoS, what is a 'forwarding class'?

Accepted Answer

A named group that maps to a specific output queue, determining how packets are buffered and scheduled for transmission

Answer

Forwarding classes in Junos CoS are logical names that map to hardware output queues (typically 0-7). Classifiers assign packets to forwarding classes, and schedulers define service parameters for each class.

Question 3

What does DSCP stand for and what is its role in Junos CoS?

Accepted Answer

Differentiated Services Code Point — a 6-bit field in the IP header used to mark packets for CoS classification

Answer

DSCP is a 6-bit field in the IP header's DSCP/ToS byte that marks packets with their desired service class. Junos uses DSCP values to classify incoming packets into forwarding classes.

Question 4

In Junos CoS, what is a 'scheduler' responsible for?

Accepted Answer

Defining the transmission priority, guaranteed bandwidth percentage, delay buffer size, and drop profile for a specific forwarding class queue

Answer

A Junos CoS scheduler defines how each forwarding class queue is serviced: how much bandwidth it gets, its transmission priority (strict-high, high, medium, low), delay buffer, and congestion drop behavior.

Question 5

What is the purpose of a Junos CoS 'rewrite rule'?

Accepted Answer

To mark or re-mark DSCP/802.1p/MPLS EXP bits in packet headers as they egress an interface, propagating CoS information downstream

Answer

Rewrite rules in Junos CoS modify the DSCP, 802.1p, or MPLS EXP code points in outgoing packet headers based on the packet's forwarding class and loss priority, propagating CoS markings to downstream devices.

JNCIA - Juniper Networks Certified Internet Associate Practice Test

JNCIA - Juniper Networks Certified Internet Associate Practice Test

JNCIA Class of Service