Dell PowerConnect J-8216 Software Guide for JUNOS version 10.3 - Page 2948

Dell PowerConnect J-Series Ethernet Switch Complete Software Guide for Junos OS Understanding CoS Two-Color Marking Networks police traffic by limiting the input or output transmission rate of a class of traffic on the basis of user-defined criteria. Policing traffic allows you to control the maximum rate of traffic sent or received on an interface and to partition a network into multiple priority levels or classes of service. Policers require you to apply limits to the traffic flow and set a consequence for packets that exceed these limits-usually a higher loss priority, so that packets exceeding the policer limits are discarded first. J-EX Series Switches support a single-rate two-color marking type of policer, which is a simplified version of Single-Rate-Three-Color marking, defined in RFC 2697, A Single Rate Three Color Marker. This type of policer meters traffic based on the configured committed information rate (CIR) and committed burst size (CBS). The single-rate two-color marker meters traffic and marks incoming packets depending on whether they are smaller than the committed burst size (CBS)-marked green-or exceed it- marked red. The single-rate two-color marking policer operates in color-blind mode. In this mode, the policer's actions are not affected by any previous marking or metering of the examined packets. In other words, the policer is "blind? to any previous coloring a packet might have had. Related • Understanding Junos OS CoS Components for J-EX Series Switches on page 2862 Documentation • Understanding the Use of Policers in Firewall Filters on page 2752 • Configuring Policers to Control Traffic Rates (CLI Procedure) on page 2788 Understanding CoS Rewrite Rules As packets enter or exit a network, edge switches might be required to alter the class-of-service (CoS) settings of the packets. This topic describes how to use rewrite rules to alter the CoS settings. It covers: • How Rewrite Rules Work on page 2876 • Default Rewrite Rule on page 2877 How Rewrite Rules Work Rewrite rules set the value of the CoS bits within the packet's header. Each rewrite rule reads the current forwarding class and loss priority associated with the packet, locates the chosen CoS value from a table, and writes this CoS value into the packet header. For rewrites to occur, rewrite rules must be explicitly assigned to an interface. Only tagged Layer 3 interfaces and tagged routed VLAN interfaces (RVIs) automatically rewrite packets by using the default IEEE 802.1p rewrite rule. Multiple rewrite rules of different types can be assigned to a single interface. 2876