Juniper EX9200 Series, Features Manual

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your network and provide different levels of service across the network—internal
forwarding and scheduling (queuing) for output—based on the forwarding class
assignments and PLP levels of the individual packets.
NOTE: Forwarding-class or loss-priority assignments performed by a policer
or a stateless firewall filter override any such assignments performed on the
ingress by the CoS default IP precedence classification at all logical interfaces
or by any configured behavior aggregate (BA) classifier that is explicitly
mapped to a logical interface.
Based on CoS configurations, packets of a given forwarding class are transmitted through
a specific output queue, and each output queue is associated with a transmission service
level defined in a
scheduler .
Based on other CoS configurations, when packets in an output queue encounter
congestion, packets with higher loss-priority values are more likely to be dropped by the
random early detection (RED) algorithm. Packet loss priority values affect the scheduling
of a packet without affecting the packet’s relative ordering within the traffic flow.
Policer Application to Traffic
After you have defined and named a policer, it is stored as a template. You can later use
the same policer name to provide the same policer configuration each time you want to
use it. This eliminates the need to define the same policer values more than once.
You can apply a policer to a traffic flow in either of two ways:
•
You can configure a standard stateless firewall filter that specifies the
policer policer-name
nonterminating action or the
three-color-policer (single-rate |
two-rate) policer-name
nonterminating action. When you apply the standard filter to
the input or output at a logical interface, the policer is applied to all packets of the
filter-specific protocol family that match the conditions specified in the filter
configuration.
With this method of applying a policer, you can define specific classes of traffic on an
interface and apply traffic rate-limiting to each class.
• You can apply a policer directly to an interface so that traffic rate-limiting applies to
all traffic on that interface, regardless of protocol family or any match conditions.
You can configure policers at the queue, logical interface, or Layer 2 (MAC) level. Only a
single policer is applied to a packet at the egress queue, and the search for policers occurs
in this order:
• Queue level
• Logical interface level
•
Layer 2 (MAC) level
7 Copyright © 2016, Juniper Networks, Inc.
Chapter 1: Understanding Traffic Policers