Default Cos Behavior On Ex Series Switches - Juniper JUNOS OS 10.3 - SOFTWARE Manual

Default CoS Behavior on EX Series Switches

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the edges of the network might be required to alter the CoS settings of the packets that
enter the network to classify the packets into the appropriate service groups.
Figure 80 on page 3147 represents the network scenario of an enterprise. Switch A is
receiving traffic from various network nodes such as desktop computers, servers,
surveillance cameras, and VoIP telephones. As each packet enters, Switch A examines
the packet's CoS settings and classifies the traffic into one of the groupings defined by
the enterprise. This definition allows Switch A to prioritize resources for servicing the
traffic streams it receives. Switch A might alter the CoS settings of the packets to better
match the enterprise's traffic groups.
When Switch B receives the packets, it examines the CoS settings, determines the
appropriate traffic groups, and processes the packets according to those settings. It then
transmits the packets to Switch C, which performs the same actions. Switch D also
examines the packets and determines the appropriate groups. Because Switch D sits at
the far end of the network, it can rewrite the CoS bits of the packets before transmitting
them.
Figure 80: Packet Flow Across the Network
If you do not configure any CoS settings on the switch, the software performs some CoS
functions to ensure that user traffic and protocol packets are forwarded with minimum
delay when the network is experiencing congestion. Some CoS settings, such as classifiers,
are automatically applied to each logical interface that you configure. Other settings,
such as rewrite rules, are applied only if you explicitly associate them with an interface.
Understanding Junos OS CoS Components for EX Series Switches on page 3148
Understanding Junos OS EZQoS for CoS Configurations on EX Series Switches on
page 3166
Example: Configuring CoS on EX Series Switches on page 3173
Example: Combining CoS with MPLS on EX Series Switches on page 3188
Chapter 107: Class of Service (CoS)—Overview
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