DSCP PHB Groups
PHB is per-hop behavior defined by RFC 2475. There are two types of PHB groups, AF and EF. AF is Assured Forwarding defined by RFC 2597. EF is Expedited Forwarding defined by RFC 2598.
AF group have 4 classes, each of them has 3 levels. The following table shows codepoint-to-PHB mapping.
AF-Table
| Class | Low Drop Precedence | Medium Drop Precedence | High Drop Precedence |
|---|---|---|---|
| AF1 | AF11(001010) | AF12(001100) | AF13(001110) |
| AF2 | AF21(010010) | AF22(010100) | AF23(010110) |
| AF3 | AF31(011010) | AF32(011100) | AF33(011110) |
| AF4 | AF41(100010) | AF42(100100) | AF43(100110) |
EF group only has one level, which is DSCP 46. The main purpose of EF is to introduce as little delay and jitter as possible.
EF-Table
| Class | Precedence |
|---|---|
| EF | DSCP 46 (101110) |
The following are output for IP DSCP.
R3(config-cmap)#match ip dscp ?
<0-63> Differentiated services codepoint value
af11 Match packets with AF11 dscp (001010)
af12 Match packets with AF12 dscp (001100)
af13 Match packets with AF13 dscp (001110)
af21 Match packets with AF21 dscp (010010)
af22 Match packets with AF22 dscp (010100)
af23 Match packets with AF23 dscp (010110)
af31 Match packets with AF31 dscp (011010)
af32 Match packets with AF32 dscp (011100)
af33 Match packets with AF33 dscp (011110)
af41 Match packets with AF41 dscp (100010)
af42 Match packets with AF42 dscp (100100)
af43 Match packets with AF43 dscp (100110)
cs1 Match packets with CS1(precedence 1) dscp (001000)
cs2 Match packets with CS2(precedence 2) dscp (010000)
cs3 Match packets with CS3(precedence 3) dscp (011000)
cs4 Match packets with CS4(precedence 4) dscp (100000)
cs5 Match packets with CS5(precedence 5) dscp (101000)
cs6 Match packets with CS6(precedence 6) dscp (110000)
cs7 Match packets with CS7(precedence 7) dscp (111000)
default Match packets with default dscp (000000)
ef Match packets with EF dscp (101110)
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