HP ProCurve Switch 6120G/XG Management Manual page 196

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Figure 5-10 shows an example of the ToS byte in the header for an IPv4 packet,
and illustrates the diffserv bits and precedence bits in the ToS byte. (Note that
the Precedence bits are a subset of the Differentiated Services bits.)
Field: Destination
MAC Address
Packet: FF FF FF FF FF FF 08 00 09 00 00 16
Figure 5-10. The ToS Codepoint and Precedence Bits
Quality of Service (QoS): Managing Bandwidth More Effectively
Using QoS Classifiers to Configure Quality of Service for Outbound Traffic
a. Configure a specific DSCP with a specific priority in an edge switch.
b. Configure the switch to mark a specific type of inbound traffic with
that DSCP (and thus create a policy for that traffic type).
c. Configure the internal switches in your LAN to honor the policy.
(For example, you could configure an edge switch to assign a codepoint
of 000001 to all packets received from a specific VLAN, and then handle
all traffic with that codepoint at high priority.)
For a codepoint listing and the commands for displaying and changing the
DSCP Policy table, refer to "Differentiated Services Codepoint (DSCP)
Mapping" on page 5-33.
Precedence Bits: This element is a subset of the DSCP and is comprised
of the upper three bits of the ToS byte. When configured to do so, the
switch uses the precedence bits to determine a priority for handling the
associated packet. (The switch does not change the setting of the prece-
dence bits.) Using the ToS Precedence bits to prioritize IPv4 packets relies
on priorities set in upstream devices and applications.
Source MAC 802.1Q Field
Address
08 00
Type & ToS Byte
Version
45 E 0
Differentiated Services Codepoint
Precedence
Bits
1 1 1 0 0
E
...
...
Rsvd.
0 0 0
0
5-25