Per-Hop Behavior - Lenovo CN4093 Application Manual

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Per-Hop Behavior

CN4093 Application Guide for N/OS 8.3

The DSCP value determines the Per Hop Behavior (PHB) of each packet. The PHB

is the forwarding treatment given to packets at each hop. QoS policies are built by

applying a set of rules to packets, based on the DSCP value, as they hop through

the network.

The CN4093 default settings are based on the following standard PHBs, as defined

in the IEEE standards:

Expedited Forwarding (EF)—This PHB has the highest egress priority and

lowest drop precedence level. EF traffic is forwarded ahead of all other traffic. EF

PHB is described in RFC 2598.

Assured Forwarding (AF)—This PHB contains four service levels, each with a

different drop precedence, as shown below. Routers use drop precedence to

determine which packets to discard last when the network becomes congested.

AF PHB is described in RFC 2597.

Class Selector (CS)—This PHB has eight priority classes, with CS7 representing

the highest priority, and CS0 representing the lowest priority, as shown below.

CS PHB is described in RFC 2474.

Class Selector