Steps for configuring QoS on the switch

Procedure
  1. Determine the QoS policy you want to implement. This includes analyzing the types of traffic flowing through your network and identifying one or more traffic types to prioritize. In order of QoS precedence, these are:
    1. UDP/TCP applications
    2. Device Priority‚ÄĒdestination or source IP address (Note that destination has precedence over source. See the table below.
    3. IP ToS Precedence Bits (Leftmost three bits in the ToS field of IP packets)
    4. IP ToS Differentiated Service bits (Leftmost 6 bits in the ToS field of IP packets)
    5. Layer 3 Protocol Priority
    6. VLAN Priority (requires at least one tagged VLAN on the network)
    7. Source-Port
    8. Incoming 802.1p Priority (requires at least one tagged VLAN on the network). In a tagged VLAN environment, the incoming 802.1p priority is used as the default QoS classifier if no QoS classifier with a higher precedence matches
  2. Select the QoS option you want to use. The following table lists the traffic types (QoS classifiers) and the QoS options you can use for prioritizing or setting a policy on these traffic types:

    QoS marking supported by QoS classifiers
    Global QoS classifiers Type of QoS marking used to prioritize outbound traffic
    802.1p Priority1 only DSCP policy2: DSCP codepoint with 802.1p priority
    UDP/TCP Supported Supported
    IP Device Supported Supported
    IP Precedence Supported3 Not Supported
    IP DiffServ Supported Supported
    L3 Protocol Supported Not Supported
    VLAN ID Supported Supported
    Source Port Supported Supported

    1When 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.

    2When 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.

    3When 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. If you want 802.1p priority settings to be included in outbound packets, ensure that tagged VLANs are configured on the appropriate downstream links.
  4. Determine the actual QoS configuration changes you will need to make on each QoS-capable device in your network in order to implement the desired policy. Also, if you want downstream devices to read and use DSCPs in IP packets from the switch, configure them to do so by enabling ToS Differentiated Service mode and making sure that the same DSCP policies are configured.