Junos Cos Components; Cos Overview - Juniper EX9200 Series Overview Manual

Junos CoS Components

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The Juniper Networks Junos
components that you can combine and tune to provide the level of services required by
customers.
The Junos OS CoS components include:
Code-point aliases—A code-point alias assigns a name to a pattern of code-point bits.
You can use this name instead of the bit pattern when you configure other CoS
components, such as classifiers, drop-profile maps, and rewrite rules.
Classifiers—Packet classification refers to the examination of an incoming packet. This
function associates the packet with a particular CoS servicing level. In the Junos OS,
classifiers associate incoming packets with a forwarding class and loss priority and,
based on the associated forwarding class, assign packets to output queues. Two
general types of classifiers are supported:
Behavior aggregate or CoS value traffic classifiers—A behavior aggregate (BA) is a
method of classification that operates on a packet as it enters the routing device.
The CoS value in the packet header is examined, and this single field determines the
CoS settings applied to the packet. BA classifiers allow you to set the forwarding
class and loss priority of a packet based on the Differentiated Services code point
(DSCP) value, DSCP IPv6 value, IP precedence value, MPLS EXP bits, and IEEE 802.1p
value. The default classifier is based on the IP precedence value.
Multifield traffic classifiers—A multifield classifier is a second method for classifying
traffic flows. Unlike a behavior aggregate, a multifield classifier can examine multiple
fields in the packet. Examples of some fields that a multifield classifier can examine
include the source and destination address of the packet as well as the source and
destination port numbers of the packet. With multifield classifiers, you set the
forwarding class and loss priority of a packet based on firewall filter rules.
Forwarding classes—The forwarding classes affect the forwarding, scheduling, and
marking policies applied to packets as they transit a routing device. The forwarding
class plus the loss priority define the per-hop behavior. Four categories of forwarding
classes are supported: best effort, assured forwarding, expedited forwarding, and
network control. For Juniper Networks M Series Multiservice Edge Routers, four
forwarding classes are supported. You can configure up to one each of the four types
of forwarding classes. For M120 and M320 Multiservice Edge Routers, Juniper Networks
MX Series 3D Universal Edge Routers, Juniper Networks T Series Core Routers and EX
Series switches, 16 forwarding classes are supported, so you can classify packets more
granularly. For example, you can configure multiple classes of expedited forwarding
(EF) traffic: EF, EF1, and EF2.
Loss priorities—Loss priorities allow you to set the priority of dropping a packet. Loss
priority affects the scheduling of a packet without affecting the packet's relative
ordering. You can use the packet loss priority (PLP) bit as part of a congestion control
strategy. You can use the loss priority setting to identify packets that have experienced
congestion. Typically you mark packets exceeding some service level with a high loss
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operating system (Junos OS) CoS consists of many
Chapter 1: CoS Overview
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