Packet Flow Through The Cos Process; Packet Flow Through The Cos Process Overview - Juniper EX9200 Series Overview Manual

CHAPTER 3

Packet Flow Through the CoS Process

Packet Flow Through the CoS Process Overview

Copyright © 2013, Juniper Networks, Inc.
Packet Flow Through the CoS Process Overview on page 15
Perhaps the best way to understand Junos CoS is to examine how a packet is treated on
its way through the CoS process. This topic includes a description of each step and figures
illustrating the process.
The following steps describe the CoS process:
A logical interface has one or more classifiers of different types applied to it (at the
1.
[edit class-of-service interfaces]
on which part of the incoming packet the classifier examines (for example, EXP bits,
IEEE 802.1p bits, or DSCP bits). You can use a translation table to rewrite the values
of these bits on ingress.
NOTE: You can only rewrite the values of these bits on ingress on the
Juniper Networks M40e, M120, M320 Multiservice Edge Routers, and T
Series Core Routers with IQE PICs. For more information about rewriting
the values of these bits on ingress, see Configuring ToS Translation Tables.
The classifier assigns the packet to a forwarding class and a loss priority (at the
2.
class-of-service classifiers]
Each forwarding class is assigned to a queue (at the
3.
hierarchy level).
forwarding-classes]
Input (and output) policers meter traffic and might change the forwarding class and
4.
loss priority if a traffic flow exceeds its service level.
The physical or logical interface has a scheduler map applied to it (at the
5.
class-of-service interfaces]
At the
[edit class-of-service interfaces]
statements affect the outgoing packets, and the
rewrite-rules
affects the incoming packets.
hierarchy level). The types of classifiers are based
hierarchy level).
[edit class-of-service
hierarchy level).
hierarchy level, the
[edit
[edit
and
scheduler-map
statement
classifiers
15