Configuring QoS globally

To globally configure a QoS policy on the switch, follow these steps:

Procedure
  1. Determine the global QoS policy to implement on the switch by analyzing the types of traffic flowing through the network and identifying one or more traffic types to prioritize. The order of precedence in which global QoS classifiers are applied, from a (highest) to h (lowest), is as follows:
    1. TCP/UDP applications.

    2. Device priority—IP source or destination address. Destination has precedence over source.

    3. IP precedence bit set (leftmost three bits in the ToS/Traffic Class field of IP packets).

    4. IP differentiated services bit set (leftmost six bits in the ToS/Traffic Class field of IP packets).

    5. Layer-3 protocol.

    6. VLAN ID. At least one tagged VLAN is required on the network.

    7. Source port.

    8. Incoming 802.1p priority (requires at least one tagged VLAN on the network).Default: In a tagged VLAN environment, the incoming 802.1p priority is used as the default QoS classifier if no global QoS classifier with a higher precedence matches.

  2. Select the global QoS classifier to use. The following table shows the types of QoS marking (802.1p priority or DSCP codepoint) supported by each global QoS classifier.
    Table 25: QoS marking supported by global QoS classifiers

    Global QoS classifiers

    Type of QoS marking used to prioritize outbound traffic

    802.1p Priority only 1

    DSCP policy – DSCP codepoint with 802.1p priority 2

    UDP/TCP

    Supported

    Supported

    IP Device

    Supported

    Supported

    IP Precedence

    Supported 3

    Not Supported

    IP DiffServ

    Supported

    Supported

    L3 Protocol

    Supported

    Not Supported

    VLAN ID

    Supported

    Supported

    Source Port

    Supported

    Supported

    1 When you configure only the 802.1p priority to mark packets that match a global QoS classifier, the selected traffic is prioritized and sent to the corresponding outbound port queue on the switch. VLAN-tagged ports are necessary to carry the 802.1p priority in a packet header to downstream devices.

    2 When you configure a DSCP policy to mark packets that match a global QoS classifier, the selected traffic is also prioritized according to the associated 802.1p priority and sent to the corresponding outbound port queue on the switch. VLAN-tagged ports carry the 802.1p priority in a packet header to downstream devices. In addition, you can configure downstream devices to read the DSCP value in IP packets and implement the service policy implied by the codepoint.

    3 When using a global QoS IP Precedence classifier, the 802.1p priority is automatically assigned to matching packets based on the IP precedence bit set in the packet header.

  3. For 802.1p priority settings to be included in outbound packets, ensure that tagged VLANs are configured on the appropriate downstream links.
  4. Determine the global QoS policy required for each QoS-capable device in the network and configure the necessary settings.

    For downstream devices to recognize and use DSCP codepoints in IP packets sent from the switch, enable ToS (Type-of-Service) Differentiated Service mode on the devices and configure the appropriate DSCP policies. Note that certain DSCP policies have a default 802.1p priority automatically assigned.