Routers support multiple forwarding classes and class-based queuing, so the concept of forwarding classes is common to all QoS policies.
Each forwarding class, also called Class of Service (CoS), is important only in relation to the other forwarding classes. A forwarding class provides network elements a method to weigh the relative importance of one packet over another in a different forwarding class.
Queues are created for a specific forwarding class to determine how the queue output is scheduled into the switch fabric. The forwarding class of the packet, along with the profile state, determines how the packet is queued and handled (the Per Hop Behavior (PHB)) at each hop along its path to a destination egress point. Routers support eight forwarding classes.
Table: Forwarding classes lists the default definitions for the forwarding classes. The forwarding class behavior, in terms of ingress marking interpretation and egress marking, can be changed by Network QoS policies. All forwarding class queues support the concept of in-profile, out-of-profile and, at egress only, inplus-profile and exceed-profile.
FC-ID |
FC name |
FC designation |
DiffServ name |
Class type |
Notes |
|---|---|---|---|---|---|
7 |
Network-Control |
NC |
NC2 |
High-Priority |
Intended for network control traffic |
6 |
High-1 |
H1 |
NC1 |
Intended for a second network control class or delay/jitter sensitive traffic |
|
5 |
Expedited |
EF |
EF |
Intended for delay/jitter sensitive traffic |
|
4 |
High-2 |
H2 |
AF4 |
Intended for delay/jitter sensitive traffic |
|
3 |
Low-1 |
L1 |
AF2 |
Assured |
Intended for assured traffic. Also, is the default priority for network management traffic. |
2 |
Assured |
AF |
AF1 |
Intended for assured traffic |
|
1 |
Low-2 |
L2 |
CS1 |
Best Effort |
Intended for BE traffic |
0 |
Best-Effort |
BE |
BE |
The forwarding classes can be classified into three class types:
High-priority or Premium
Assured
Best-Effort