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Quality of Service: Managing Bandwidth More Effectively
Globally-Configured QoS
Table 6-8. IP Precedence-to-802.1p Priority Mapping
ToS/Traffic Class Byte:
IP Precedence Bits
Corresponding
802.1p Priority
Service Priority Level
000 1 Lowest
001 2 Low
002 0 Normal
003 3
004 4
005 5
006 6
007 7 Highest
Note Using a global IP-Precedence classifier to prioritize IP packets relies on
priorities set in upstream devices and applications.
Figure 6-13 shows the difference between the diffserv bits and precedence
bits in an IPv4 ToS byte and an IPv6 Traffic Class byte. Note that:
■ Precedence bits are a subset of the Differentiated Services bits.
■ The rightmost two bits are reserved.
IPv4 Fields: Destination MAC
Address
Source MAC
Address
802.1Q Field Type and
Version
Type-of-Service
Byte
…
Sample IPv4
Packet:
FF FF FF FF FF FF 08 00 09 00 00 16 08 00 45
E 0
...
IPv6 Fields: Destination MAC
Address
Source MAC
Address
...
Traffic Class
Byte
…
Sample IPv6
Packet:
FF FF FF FF FF FF 2001:db8:260:0212::
01b4
...
E 0
...
Figure 6-13. IPv4 ToS/IPv6 Traffic Class Byte with DSCP Codepoint and Precedence Bits
Differentiated Services Codepoint
Rsvd.
Precedence
Bits
Delay Throughput
Reliability Bits
1 1 1 0 0 0 0 0
E 0
6-43