Quality of Service (QoS): Managing Bandwidth More Effectively

Using QoS Classifiers To Configure Quality of Service for Outbound Traffic

QoS IP Type-of-Service (ToS) Policy and Priority

QoS Classifier Precedence: 3

This feature applies only to IP traffic and performs either of the following:

ToS IP-Precedence Mode: All IP packets generated by upstream devices and applications include precedence bits in the ToS byte. Using this mode, the switch uses these bits to compute and assign the corresponding 802.1p priority.

ToS Differentiated Services (Diffserv) Mode: This mode requires knowledge of the codepoints set in IP packets by the upstream devices and applications. It uses the ToS codepoint in IP packets coming from upstream devices and applications to assign 802.1p priorities to the pack­ ets. You can use this option to do both of the following:

•Assign a New Prioritization Policy: A “policy” includes both a codepoint and a corresponding 802.1p priority. This option selects an incoming IP packet on the basis of its codepoint and assigns a new codepoint and corresponding 802.1p priority. (Use the qos dscp-mapcommand to specify a priority for any codepoint—page15-51.)

•Assign an 802.1p Priority: This option reads the DSCP of an incoming IP packet and, without changing this codepoint, assigns the 802.1p priority to the packet, as configured in the DSCP Policy Table (page 15-51). This means that a priority value of 0 - 7 must be configured for a DSCP before the switch will attempt to perform a QoS match on the packet’s DSCP bits.

Before configuring the ToS Diffserv mode, you must use the dscp-mapcommand to configure the desired 802.1p priorities for the codepoints you want to use for either option. This command is illustrated in the following examples and is described under “Differentiated Services Codepoint (DSCP) Mapping” on page 15-51.

Unless IP-Precedence mode and Diffserv mode are both disabled (the default setting), enabling one automatically disables the other. For more on ToS operation, refer to “Details of QoS IP Type-of-Service” on page 15-34.

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