This section contains the following topics:
Behavior aggregate classifiers use CoS values such as DiffServ code points (DSCPs), DSCP IPv6, IP precedence, IEEE 802.1 and MPLS experimental (EXP) bits to associate incoming packets with a particular CoS servicing level. On a Services Router, you can assign a meaningful name or alias to the CoS values and use this alias instead of bits when configuring CoS components. These aliases are not part of the specifications but are well-known through usage. For example, the alias for DSCP 101110 is widely accepted as ef (expedited forwarding). For information about defining CoS value aliases, see Configuring Class of Service.
Table 103 shows the CoS values and the associated well-known aliases.
Table 103: Well-Known CoS Aliases and CoS Values
J-series Services Routers have eight queues built into the hardware. If a classifier does not assign a packet to any other queue, the packet is assigned by default to the class associated with queue 0.
By default, four queues are assigned to four forwarding classes. Table 104 shows the four default forwarding classes and queues that Juniper Networks classifiers assign to packets based on the CoS values in arriving packet headers. Queues 4 through 7 have no default assignments to forwarding classes. To use queues 4 through 7, you must create custom forwarding class names and assign them to the queues. For more information about how to assign queues to forwarding classes, see the Configuring Class of Service.
Table 104: Default Forwarding Class Queue Assignments
Each forwarding class has an associated scheduler priority. Only two forwarding classes, best-effort and network-control (queue 0 and queue 3), are used in the JUNOS default scheduler configuration.
By default, the best-effort forwarding class (queue 0) receives 95 percent, and the network-control (queue 3) receives 5 percent of the bandwidth and buffer space for the output link. The default drop profile causes the buffer to fill and then discard all packets until it again has space.
The expedited-forwarding and assured-forwarding classes have no schedulers, because by default no resources are assigned to queue 1 and queue 2. However, you can manually configure resources for expedited-forwarding and assured-forwarding.
The default scheduler settings are automatically included in the configuration, but they do not appear in the output of the show class-of-service command.
- [edit class-of-service]
- schedulers {
-
- network-control {
- transmit-rate percent 5;
- buffer-size percent 5;
- priority low;
- drop-profile-map loss-priority any protocol any drop-profile terminal;
- }
-
- best-effort {
- transmit-rate percent 95;
- buffer-size percent 95;
- priority low;
- drop-profile-map loss-priority any protocol any drop-profile terminal;
- }
- }
- drop-profiles {
-
- terminal {
-
-
- fill-level 100 drop-probability 100;
- }
- }
You can modify the default settings through configuration. For instructions, see Configuring Class of Service.
Table 105 shows the forwarding class and packet loss priority (PLP) that are assigned by default to each well-known DSCP. Although several DSCPs map to the expedited-forwarding (ef) and assured-forwarding (af) classes, by default no resources are assigned to these forwarding classes. All af classes other than af1x are mapped to best-effort, because RFC 2597, Assured Forwarding PHB Group, prohibits a node from aggregating classes. Assignment to best-effort implies that the node does not support that class.
You can modify the default settings through configuration. For instructions, see Configuring Class of Service.
Table 105: Default Behavior Aggregate Classification
Typically, a router rewrites CoS values in outgoing packets on the outbound interfaces of an edge router. The marker rewrites the CoS values to meet the policies of the targeted peer. It reads the current forwarding class and loss priority information associated with the packet, locates the chosen CoS value from a table, and writes this CoS value into the packet header.
For instructions for configuring rewrite rules, see Configuring and Applying Rewrite Rules .
Table 106 shows the router forwarding classes associated with each well-known DSCP code point and the resources assigned to their output queues for a sample DiffServ CoS implementation. This example assigns expedited forwarding to queue 1 and a subset of the assured forwarding classes (af1x) to queue 2, and distributes resources among all four forwarding classes.
Other DiffServ-based implementations are possible. For configuration information, see Configuring Class of Service.
Table 106: Sample Behavior Aggregate Classification Forwarding Classes and Queues