[Contents]
[Prev]
[Next]
[Index]
[Report an Error]
JUNOS CoS Functions
On a Services Router, you configure CoS functions using different
components. These components are configured individually or in a combination
to define particular CoS services. Figure 17 displays
the relationship of different CoS components to each other and illustrates
the sequence in which they interact. Table 87 defines
the components and explains their use.
Figure 17: Packet Flow Through JUNOS CoS-Configurable
Components
Each box in Figure 17 represents a CoS
component. The solid lines show the direction of packet flow in a router.
The upper row indicates an incoming packet and the lower row an outgoing packet.
The dotted lines show the inputs and outputs of particular CoS components.
For example, the forwarding class and loss priority are outputs of behavior
aggregate classifiers and multifield classifiers and inputs for rewrite markers
and schedulers.
Typically, only a combination of some components shown in Figure 17 (not
all) is used to define a CoS service offering. For example, if a packet's
class is determined by a behavior aggregate classifier, it is associated with
a forwarding class and loss priority and does not need further classification
by the multifield classifier.
Table 87: JUNOS CoS Components
|
Classifiers
|
Associate incoming packets with a forwarding class and packet loss priority
(PLP). The following types of classifiers are available:
- Behavior aggregate (BA) or code point traffic classifiers—Allow
you to set the forwarding class and PLP based on DSCP.
- Multifield (MF) traffic classifiers—Allow you to set the
forwarding class and PLP based on firewall filter rules. Classification is
usually done at the edge of the network for packets that do not have valid
CoS values in the packet headers.
|
|
Forwarding classes
|
Allow you to set the scheduling and marking of packets as they transit
the Services Router. Known as ordered aggregates in the DiffServ architecture,
the forwarding class plus the loss priority determine the router’s per-hop
behavior (PHB in DiffServ) for CoS.
|
|
Loss priorities
|
Allow you to set the priority of dropping a packet before it is sent.
Loss priority affects the scheduling of a packet without affecting the packet’s
relative ordering.
|
|
Forwarding policy options
|
- Allow you to associate forwarding classes with next hops.
- Allow you to create classification overrides, which assign forwarding
classes to sets of prefixes.
|
|
Transmission scheduling and rate control
|
Provide you with a variety of tools to manage traffic flows. The following
types are available:
- Schedulers—Allow you to 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. Drop profiles are
useful for the assured forwarding service class.
- Fabric schedulers—For M320 and T-series platforms only,
fabric schedulers allow you to identify a packet as high or low priority based
on its forwarding class, and to associate schedulers with the fabric priorities.
- Policers for traffic classes—Allow you to 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 or to a different loss priority, or to both. You define policers with
filters that can be associated with input or output interfaces. Policers are
useful for the expedited forwarding service class.
|
|
Rewrite markers
|
Allow you to redefine the CoS 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.
|
[Contents]
[Prev]
[Next]
[Index]
[Report an Error]