Supported CoS Standards and Features

For interfaces that carry IPv4, IPv6, or MPLS traffic, JUNOS CoS features provide multiple classes of service for different applications. You can configure multiple forwarding classes for transmitting packets, defining which packets are placed into each output queue, scheduling the transmission service level for each queue, and managing congestion using a Random Early Detection (RED) algorithm.

JUNOS CoS features are supported on all interface types except the following:

• cau4—Channelized STM1 IQ interface (configured on the Channelized STM1 IQ PIC)
• coc1—Channelized OC1 IQ interface (configured on the Channelized OC12 IQ PIC)
• coc12—Channelized OC12 IQ interface (configured on the Channelized OC12 IQ PIC)
• cstm-1—Channelized STM1 IQ interface (configured on the Channelized STM1 IQ PIC)
• ct1—Channelized T1 IQ interface (configured on the Channelized DS3 IQ PIC or Channelized OC12 IQ PIC)
• ct3—Channelized T3 IQ interface (configured on the Channelized DS3 IQ PIC or Channelized OC12 IQ PIC)
• ce1—Channelized E1 IQ interface (configured on the Channelized E1 IQ PIC or Channelized STM1 IQ PIC)
• dsc—Discard interface
• fxp—Management and internal Ethernet interfaces
• lo—Loopback interface, which is internally generated
• pd—Interface that de-encapsulates packets on a Platform Independent Multicast (PIM) rendezvous point (RP) routing platform
• pe—Interface on a first-hop RP that encapsulates packets destined for the RP routing platform
• vt—Virtual loopback tunnel interface

JUNOS CoS applications support the following range of mechanisms:

• Differentiated Services (DiffServ)—Implemented as six bits of the type-of-service (ToS) byte in the IP header. The JUNOS software uses DiffServ code points (DSCPs) in the IP ToS field to determine the forwarding class associated with each packet.
• Two-rate tricolor marking—For T-series platforms with Enhanced II FPCs, you can configure CoS traffic policing using two-rate tricolor marking (trTCM), which provides three levels of drop precedence (also called packet loss priority [PLP]). Two-rate TCM is a “color-aware” method of traffic policing—high, medium, and low loss priorities are mapped to the colors red, yellow, and green. The color of a packet, which is used or set by the TCM policer, corresponds to the packet’s loss priority. trTCM is defined in RFC 2698, A Two Rate Three Color Marker.
• Layer 2 to Layer 3 CoS mapping—JUNOS CoS applications substantially support setting a Layer 3 packet’s forwarding class and loss priority value based on information in the Layer 2 packet header. Output involves mapping the forwarding class and loss priority value to a Layer 2-specific marking. You can configure the JUNOS software to mark the Layer 2 and Layer 3 headers simultaneously.
• MPLS EXP—JUNOS CoS applications support mapping of MPLS experimental (EXP) bit settings to forwarding classes and vice versa.
• VPN outer label marking—JUNOS CoS applications support setting of outer label EXP bits based on MPLS EXP mapping.

JUNOS CoS features include the following:

• Classifiers—Assign incoming packets to a forwarding class and loss priority, and direct packets to output queues based on the forwarding class. Two general types of classifiers are supported:

  • Behavior aggregate (BA) or code point traffic classifiers—Determine each packet’s forwarding class and loss priority. BA classifiers allow setting of the forwarding class and loss priority of a packet based on DSCP bits, IP precedence bits, MPLS EXP bits, and IEEE 802.1p bits. The default classifier is based on IP precedence bits.
  • Multifield (MF) traffic classifiers—Set a packet’s forwarding class and loss priority based on packet filter rules.
• Forwarding classes—Determine the forwarding, scheduling, and marking policies applied to packets as they transit the routing platform. Four forwarding classes are supported: best effort, assured forwarding, expedited forwarding, and network control. Together with loss priority, the forwarding class defines the per-hop behavior.
• Forwarding policy options—Associate forwarding classes with next hops. Also enable creation of classification overrides, which assign forwarding classes to sets of prefixes.
• Loss priorities—Set a packet’s priority to be discarded. Typically, packets exceeding some service level are marked with a high loss priority. Loss priority affects the scheduling of a packet. Loss priority is set by configuring a classifier or a policer.
• Oversubscribing interface bandwidth (Gigabit Ethernet IQ and Channelized IQ PICs)—Configures shaping rates so that their sum exceeds the physical Ethernet bandwidth.
• Rewrite markers—Change the code-point value of outgoing packets. Rewriting, or marking, outbound packets is useful when the routing platform is at the border of a network and must alter the code points to meet the policies of the targeted peer.
• Simple filters for metropolitan Ethernet applications (4-port and 8-port Gigabit Ethernet IQ2 PICs only)—Classify IPv4 traffic based on noncomplex filters.

• Transmission scheduling and rate control—Provides a variety of tools to manage traffic flows:

  • Schedulers—Define the priority, bandwidth, delay buffer size, rate control status, and RED drop profiles to be applied to a particular forwarding class for packet transmission.
  • Fabric schedulers (T-series platforms only)—Identify a packet as high or low priority based on its forwarding class.
  • Policers—Limit traffic of a certain class to a specified bandwidth and burst size. Packets exceeding the policer limits can be discarded, or can be assigned to a different forwarding class, to a different loss priority, or to both. Policers are defined with filters that can be associated with either input or output interfaces.
• Virtual channels and virtual channel groups (J-series Services Routers only)—Direct traffic into a virtual channel and apply bandwidth limits to the channel.

The JUNOS software substantially supports the following CoS standards:

• RFC 2474, Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers
• RFC 2475, An Architecture for Differentiated Services
• RFC 2597, Assured Forwarding PHB Group
• RFC 2598, An Expedited Forwarding PHB
• RFC 2697, A Single Rate Three Color Marker
• RFC 2698, A Two Rate Three Color Marker

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