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Traffic Policer Types

 

Single-Rate Two-Color Policers

You can use a single-rate two-color policer, or “policer” when used without qualification, to rate-limit a traffic flow to an average bits-per-second arrival rate (specified by the single specified bandwidth limit) while allowing bursts of traffic for short periods (controlled by the single specified burst-size limit). This type of policer categorizes a traffic flow as either green (conforming) or red (nonconforming). Packets in a green flow are implicitly set to a low loss priority and then transmitted. Packets in a red flow are handled according to actions specified in the policer configuration. Packets in a red flow can be marked—set to a specified forwarding class, set to a specified loss priority, or both—or they can be discarded.

A single-rate two-color policer is most useful for metering traffic at the port (physical interface) level.

Basic Single-Rate Two-Color Policer

You can apply a basic single-rate two-color policer to Layer 3 traffic in either of two ways: as an interface policer or as a firewall filter policer. You can apply the policer as an interface policer, meaning that you apply the policer directly to a logical interface at the protocol family level. If you want to apply the policer to selected packets only, you can apply the policer as a firewall filter policer, meaning that you reference the policer in a stateless firewall filter term and then apply the filter to a logical interface at the protocol family level.

Bandwidth Policer

A bandwidth policer is simply a single-rate two-color policer that is defined using a bandwidth limit specified as a percentage value rather than as an absolute number of bits per second. When you apply the policer (as an interface policer or as a firewall filter policer) to a logical interface at the protocol family level, the effective bandwidth limit is calculated based on either the physical interface media rate or the logical interface configured shaping rate.

Logical Bandwidth Policer

A logical bandwidth policer is a bandwidth policer for which the effective bandwidth limit is calculated based on the logical interface configured shaping rate. You can apply the policer as a firewall filter policer only, and the firewall filter must be configured as an interface-specific filter. When you apply an interface-specific filter to multiple logical interfaces on supported routing platforms, any count or policer actions act on the traffic stream entering or exiting each individual interface, regardless of the sum of traffic on the multiple interfaces.

Three-Color Policers

The Junos OS supports two types of three-color policers: single-rate and two-rate. The main difference between a single-rate and a two-rate policer is that the single-rate policer allows bursts of traffic for short periods, while the two-rate policer allows more sustained bursts of traffic. Single-rate policing is implemented using a single token-bucket model, so that periods of relatively low traffic must occur between traffic bursts to allow the token bucket to refill. Two-rate policing is implemented using a dual token-bucket model, which allows bursts of traffic for longer periods.

Single-Rate Three-Color Policers

The single-rate three-color type of policer is defined in RFC 2697, A Single Rate Three Color Marker. You use this type of policer to rate-limit a traffic flow to a single rate and three traffic categories (green, yellow, and red). A single-rate three-color policer defines a committed bandwidth limit and burst-size limit plus an excess burst-size limit. Traffic that conforms to the committed traffic limits is categorized as green (conforming). Traffic that conforms to the bandwidth limit while allowing bursts of traffic as controlled by the excess burst-size limit is categorized as yellow. All other traffic is categorized as red.

A single-rate three-color policer is most useful when a service is structured according to packet length, not peak arrival rate.

Two-Rate Three-Color Policers

The two-rate three-color type of policer is defined in RFC 2698, A Two Rate Three Color Marker. You use this type of policer to rate-limit a traffic flow to two rates and three traffic categories (green, yellow, and red). A two-rate three-color policer defines a committed bandwidth limit and burst-size limit plus a peak bandwidth limit and burst-size limit. Traffic that conforms to the committed traffic limits is categorized as green (conforming). Traffic that exceeds the committed traffic limits but remains below the peak traffic limits is categorized as yellow. Traffic that exceeds the peak traffic limits is categorized as red.

A two-rate three-color policer is most useful when a service is structured according to arrival rates and not necessarily packet length.

Hierarchical Policers

You can use a hierarchical policer to rate-limit ingress Layer 2 traffic at a physical or logical interface and apply different policing actions based on whether the packets are classified for expedited forwarding (EF) or for a lower priority output queue. This feature is supported on SONET interfaces hosted on M40e, M120, and M320 edge routers with incoming Flexible PIC Concentrators (FPCs) as SFPC and outgoing FPCs as FFPC, and on T320, T640, and T1600 core routers with Enhanced Intelligent Queuing (IQE) PICs.

Two-Color and Three-Color Policer Options

Both two-color and three-color policers can be configured with the following options:

Logical Interface (Aggregate) Policers

A logical interface policer—also called an aggregate policer—is a two-color or three-color policer that you can apply to multiple protocol families on the same logical interface without creating multiple instances of the policer. You apply a logical interface policer directly to a logical interface configuration (and not by referencing the policer in a stateless firewall filter and then applying the filter to the logical interface).

  • You can apply the policer at the interface logical unit level to rate-limit all traffic types, regardless of the protocol family.

    When applied in this manner, the logical interface policer will be used by all traffic types (inet, intet6, etc.) and across all layers (layer 2, layer 3) no matter where the policer is attached on the logical interface.

  • You can also apply the policer at the logical interface protocol family level, to rate-limit traffic for a specific protocol family.

You can apply a logical interface policer to unicast traffic only. For information about configuring a stateless firewall filter for flooded traffic, see “Applying Forwarding Table Filters” in the “Traffic Sampling, Forwarding, and Monitoring” section of the Routing Policies, Firewall Filters, and Traffic Policers User Guide.

Physical Interface Policers

A physical interface policer is a two-color or three-color policer that applies to all logical interfaces and protocol families configured on a physical interface, even if the logical interfaces belong to different routing instances. You apply a physical interface policer to a logical interface at the protocol level through a physical interface filter only, but rate limiting is performed aggregately for all logical interfaces and protocol families configured on the underlying physical interface.

This feature enables you to use a single policer instance to perform aggregate policing for different protocol families and different logical interfaces on the same physical interface.

Policers Applied to Layer 2 Traffic

In addition to hierarchical policing, you can also apply single-rate two-color policers and three-color policers (both single-rate and two-rate) to Layer 2 input or output traffic. You must configure the two-color or three-color policer as a logical interface policer and reference the policer in the interface configuration at the logical unit level, and not at the protocol level. You cannot apply a two-color or three-color policer to Layer 2 traffic as a stateless firewall filter action.

Multifield Classification

Like behavior aggregate (BA) classification, which is sometimes referred to as class-of-service (CoS) value traffic classification, multifield classification is a method of classifying incoming traffic by associating each packet with a forwarding class, a packet loss priority level, or both. The CoS scheduling configuration assigns packets to output queues based on forwarding class. The CoS random early detection (RED) process uses the drop probability configuration, output queue fullness percentage, and packet loss priority to drop packets as needed to control congestion at the output stage.

BA classification and multifield classification use different fields of a packet to perform traffic classification. BA classification is based on a CoS value in the IP packet header. Multifield classification can be based on multiple fields in the IP packet header, including CoS values. Multifield classification is used instead of BA classification when you need to classify packets based on information in the packet other than the CoS values only. Multifield classification is configured using a stateless firewall filter term that matches on any packet header fields and associates matched packets with a forwarding class, a loss priority, or both. The forwarding class or loss priority can be set by a firewall filter action or by a policer referenced as a firewall filter action.