[Contents]
[Prev]
[Next]
[Index]
[Report an Error]
Configuring Tricolor 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.
Juniper Networks routing platform architectures
can support three types of policer:
- Two-color—A two-color policer (or “policer”
when used without qualification) meters the traffic stream and classifies
packets into two categories of packet loss priority (PLP) according
to a configured bandwidth and burst-size limit. You can mark packets
that exceed the bandwidth and burst-size limit in some way, or simply
discard them. A policer is most useful for metering traffic at the
port (physical interface) level.
- Single-Rate Tricolor Marking (srTCM)—This type of
policer is defined in RFC 2697, A Single Rate Three
Color Marker, as part of an assured forwarding (AF) per-hop-behavior
(PHB) classification system for a Differentiated Services (DiffServ)
environment. This type of policer meters traffic based on the configured
committed information rate (CIR), committed burst size (CBS), and
the excess burst size (EBS). Traffic is marked as belonging to one
of three categories (green, yellow, or red) based on whether the packets
arriving are below the CBS (green), exceed the CBS (yellow) but not
the EBS, or exceed the EBS (red). Single-rate TCM is most useful when
a service is structured according to packet length and not peak arrival
rate.
- Two-rate Tricolor Marking (trTCM)—This type of policer
is defined in RFC 2698, A Two Rate Three Color Marker, as part of an assured forwarding (AF) per-hop-behavior (PHB) classification
system for a Differentiated Services (DiffServ) environment. This
type of policer meters traffic based on the configured CIR and peak
information rate (PIR), along with their associated burst sizes, the
CBS and peak burst size (PBS). Traffic is marked
as belonging to one of three categories (green, yellow, or red) based
on whether the packets arriving are below the CIR (green), exceed
the CIR (yellow) but not the PIR, or exceed the PIR (red). Two-rate
TCM is most useful when a service is structured according to arrival
rates and not necessarily packet length.
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
TCM is not bound by a green-yellow-red coloring
convention. Packets are usually marked with low, medium, or high PLP
bit configurations based on color, so both TCM 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
TCM schemes can operate in two modes:
- Color-blind—In color-blind mode, the TCM policer
assumes that all packets examined have not been previously marked
or metered. In other words, the TCM is “blind” to any
previous coloring a packet might have had.
- Color-aware—In color-aware mode, the TCM policer
assumes that all packets examined have been previously marked or metered.
In other words, the TCM is “aware” of the previous coloring
a packet might have had. In color-aware mode, the TCM policer can
increase the PLP of a packet, but never decrease it. For example,
if a color-aware TCM 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 you use the naming convention policertypeTCM#-color type when configuring
TCM policers. Because policers can be numerous and must be applied
correctly to work, a simple naming convention makes it easier to apply
the TCM policers properly.
|
For example, the first single-rate, color-aware
TCM configured would be named srTCM1-ca. The second two-rate,
color-blind TCM configured would be named trTCM2-cb.
This chapter discusses the following topics:
[Contents]
[Prev]
[Next]
[Index]
[Report an Error]
