Color Modes for Three-Color Policers
Three-color policers are not bound by a green-yellow-red coloring convention. Packets are marked with low, medium-high, or high packet loss priority (PLP) bit configurations based on color, so both three-color policer schemes extend the functionality of class-of-service (CoS) traffic policing by providing three levels of drop precedence (loss priority) instead of the two normally available in port-level policers. Both single-rate and two-rate three-color policer schemes can operate in two modes:
- Color-blind—In color-blind mode, the three-color policer assumes that all packets examined have not been previously marked or metered. In other words, the three-color policer is “blind” to any previous coloring a packet might have had.
- Color-aware—In color-aware mode, the three-color
policer assumes that all packets examined have been previously marked
or metered. In other words, the three-color policer is “aware”
of the previous coloring a packet might have had. In color-aware mode,
the three-color policer can increase the PLP of a packet, but never
decrease it. For example, if a color-aware three-color policer meters
a packet with a medium PLP marking, it can raise the PLP level to
high, but cannot reduce the PLP level to low.
Note: We recommend that you use the naming convention policertypeTCM#-color type when configuring three-color policers and policer# when configuring two-color policers. TCM stands for three-color marker. Because policers can be numerous and must be applied correctly to work, a simple naming convention makes it easier to apply the policers properly.
For example, the first single-rate, color-aware three-color policer configured would be named srTCM1-ca. The second two-rate, color-blind three-color policer configured would be named trTCM2-cb.
