Quality of Service (QoS): Managing Bandwidth More Effectively

Using QoS Classifiers To Configure Quality of Service for Outbound Traffic

Assigning an 802.1p Priority to IP 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 IP 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.

IP Precedence Syntax: qos type-of-service ip-precedence

Causes the switch to automatically assign an 802.1p priority to all IP 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 in a tagged VLAN, it carries the 802.1p priority with it to the next downstream device. (ToS IP Prece­ dence 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 configura­ tion status. If diff-services is enabled, lists code- point data as described under “Assigning a DSCP Policy on the Basis of the DSCP in IP Packets Received from Upstream Devices” on page 15-31.

With this option, prioritization of outbound packets relies on the IP-Prece­ dence 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 15-11. Example of Enabling ToS IP-Precedence Prioritization

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