Extreme Networks ExtremeWare 7.2e, Installation And User Manual

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118 ExtremeWare 7.2e Installation and User Guide
Quality of Service (QoS)
Figure 19: IP packet header encapsulation
Observing DiffServ Information
When a packet arrives at the switch on an ingress port, the switch examines the first six of eight TOS
bits, called the code point. The switch can assign the QoS profile used to subsequently transmit the
packet based on the code point. The QoS profile controls a hardware queue used when transmitting the
packet out of the switch, and determines the forwarding characteristics of a particular code point.
Viewing DiffServ information can be enabled or disabled; by default it is disabled.
To enable DiffServ information, use the following command:
enable diffserv examination ports [<portlist> | all]
To disable DiffServ information, use the following command:
disable diffserv examination ports [<portlist> | all]
NOTE
After DiffServ information is enabled, the ACL router cannot apply for the same port.
Changing DiffServ Code point assignments in the Q0S Profile
Because the code point uses six bits, it has 64 possible values (2
6
= 64). Be default, the values are
grouped and assigned to the default QoS profiles listed in Table 25.
Table 25: Default Code Point-to-QoS Profile Mapping
Code Point QoS Profile
0-7 Qp1
EW_023
Type-of-service
DiffServ code point
IHL
Data (variable)
0 bits 31
Options (+ padding)
Destination address
Source address
0 7 6 5 4 3 2 1
Total length Version
Protocol Time-to-live Header checksum
Flags Identification Fragment offset