Per Hop Behavior - Lenovo RackSwitch G8264 Application Manual

Per Hop Behavior

© Copyright Lenovo 2016
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 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 in the following table. Routers use drop
precedence to determine which packets to discard last when the network
becomes congested. AF PHB is described in RFC 2597.
Drop Class 1
Precedence
Low AF11 (DSCP 10)
Medium AF12 (DSCP 12)
High AF13 (DSCP 14)
 Class Selector (CS)—This PHB has eight priority classes, with CS7 representing
the highest priority, and CS0 representing the lowest priority, as shown in the
following table. CS PHB is described in RFC 2474.
Priority Class Selector
Highest
Lowest
Class 2
AF21 (DSCP 18) AF31 (DSCP 26)
AF22 (DSCP 20) AF32 (DSCP 28)
AF23 (DSCP 22) AF33 (DSCP 30)
DSCP
CS7 56
CS6 48
CS5 40
CS4 32
CS3 24
CS2 16
CS1 8
CS0 0
Class 3 Class 4
AF41 (DSCP 34)
AF42 (DSCP 36)
AF43 (DSCP 38)
Chapter 13: Quality of Service
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