Quality of Service (QoS): Managing Bandwidth More Effectively

Using QoS Classifiers To Configure QoS for Outbound Traffic

Assigning an 802.1p Priority to IPv4 Packets on the Basis of the ToS Precedence Bits

If a device or application upstream of the switch sets the precedence bits in the ToS byte of IPv4 packets, you can use this feature to apply that setting for prioritizing packets for outbound port queues. If the outbound packets are in a tagged VLAN, this priority is carried as an 802.1p value to the adjacent downstream devices.

Syntax: qos type-of-service ip-precedence

Causes the switch to automatically assign an 802.1p priority to all IPv4 packets by computing each packet’s 802.1p priority from the precedence bits the packet carries. This priority determines the packet’s queue in the outbound port to which it is sent. If the packet leaves the switch on a tagged port, it carries the 802.1p priority with it to the next downstream device. (ToS IP Precedence Default: Disabled)

no qos type-of-service

Disables all ToS classifier operation, including prioritization using the precedence bits.

show qos type-of-service

When ip-precedence is enabled (or if neither ToS option is configured), shows the ToS configuration status. If diff­ services is enabled, lists codepoint data as described under “Assigning a DSCP Policy on the Basis of the DSCP in IPv4 Packets Received from Upstream Devices” on page 6-40.

With this option, prioritization of outbound packets relies on the IP- Precedence bit setting that IP packets carry with them from upstream devices and applications. To configure and verify this option:

 

 

 

 

Default ToS Configuration

 

Current ToS Configuration

 

 

 

 

 

 

 

 

 

Figure 6-14. Example of Enabling ToS IP-Precedence Prioritization

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