DiffServ-Based Traffic Groups

DiffServ-based traffic groups forward traffic to egress QoS profiles based on the type-of-service (TOS) or traffic class (TC) information in an IP packet. In many systems, this TOS or TC information is replaced with a DiffServ field that uses six of the eight bits for a DiffServ code point (DSCP) as shown in the following figure. (The other two bits are not used.)

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DiffServe Code Point

Because the DSCP uses six bits, it has 64 possible values (2^6 = 64). By default, the values are grouped and assigned to the default QoS profiles as listed in the following table.

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Default DSCP-to-QoS-Profile Mapping

Traffic Group Code Point SummitStack and Summit Family Switches QoS Profile
0-7 QP1
8-15 QP1
16-23 QP1
24-31 QP1
32-39 QP1
40-47 QP1
48-55 QP1
56-63 QP8


The default DiffServ examination mappings apply on ports in more than one virtual router (VR). If you attempt to configure DiffServe examination or replacement on a port that is in more than one virtual router, the system returns the following message:
Warning: Port belongs to more than one VR. Port properties related to diff serv and code replacement will not take effect.

You do not need to define these traffic groups. You can enable or disable the use of these traffic groups by enabling or disabling the DiffServ examination feature as described in Configuring a DiffServ-Based Traffic Group. You can also configure which DSCP values map to which queues.



When DiffServ examination is enabled on 1 Gigabit Ethernet ports, 802.1p replacement is enabled and cannot be disabled. The ingress 802.1p value is replaced with the 802.1p value assigned to the egress QoS profile.

A related feature is the DiffServ replacement feature, which allows you to configure the software to replace the DSCP in an ingress frame with a different value in the egress frame. For more information on DiffServ replacement, see Configuring 802.1p or DSCP Replacement.