Egress QoS profiles are supported on all ExtremeXOS switches and allow you to provide dual-rate egress rate-shaping for all traffic groups on all egress ports. Any configuration you apply to an egress QoS profile is applied to the same egress QoS profile on all other ports, unless a QoS profile parameter has been overridden for a port.
When you are configuring ACL-based traffic groups, you can use the qosprofile action modifier to select an egress QoS profile. For DiffServ-, port-, and VLAN-based traffic groups, the traffic group configuration selects the egress QoS profile. For CoS dot1p traffic groups on all platforms, the dot1p value selects the egress QoS profile.
Egress QoS profile operation depends on the switch type and is described in the following sections.
BlackDiamond X8 series switches, BlackDiamond 8800 series switches, SummitStack, and Summit family switches have two default egress QoS profiles named QP1 and QP8. You can configure up to six additional QoS profiles (QP2 through QP7) on the switch. However, on a SummitStack, you cannot create QoS profile QP7, as this profile is reserved for system control traffic. The default settings for egress QoS profiles are summarized in the following table.
Default QoS Profile Parameters on all Platforms
| Ingress 802.1p Priority Value | Egress QoS Profile Name | Queue Service Priority Value | Buffer | Weight | Notes |
|---|---|---|---|---|---|
| 0-6 | QP1 | 1 (Low) | 100% |
1 |
This QoS profile is part of the default configuration and cannot be deleted. |
| QP2 | 2 (LowHi) | 100% | 1 | You must create this QoS profile before using it. | |
| QP3 | 3 (Normal) | 100% | 1 | You must create this QoS profile before using it. | |
| QP4 | 4 (NormalHi) | 100% | 1 | You must create this QoS profile before using it. | |
| QP5 | 5 (Medium) | 100% | 1 | You must create this QoS profile before using it. | |
| QP6 | 6 (MediumHi) | 100% | 1 | You must create this QoS profile before using it. | |
| QP7 | 7 (High) | 100% | 1 | You must create this QoS profile before using it. You cannot create this QoS profile on SummitStack. | |
| 7 | QP8 | 8 (HighHi) | 100% | 1 | This QoS profile is part of the default configuration and cannot be deleted. |
For CoS 802.1p traffic groups, the ingress 802.1p priority value selects a specific QoS profile as shown in the table above. This mapping can be changed as described in Changing the 802.1p Priority to QoS Profile Mapping. For traffic groups other than 802.1p-based groups, the traffic group configuration selects a specific egress QoS profile by name.
The default dual-rate QoS configuration is 0% for minimum bandwidth and 100% for maximum bandwidth.
The QoS profile for each port receives a default buffer reservation. All unreserved buffer space is part of a buffer pool, which can be used by QoS profiles when reserved space runs out, provided that the configuration for that QoS profile and port allows it.
You can increase the size of the shared buffer pool by reducing the global buffer reservation for a QoS profile on all switch ports. You can restrict buffer usage for a QoS profile in amounts ranging from 1 to 100%, in whole integers.
You can also override the global buffer reservation to increase or decrease the buffer space allotment for a specific QoS profile on one or more ports. Using the buffer override feature, you can override the global setting to use from 1–10,000% of the configured global allotment. The system does not drop any packets as long as reserved packet buffer memory for the port and QoS profile or shared packet memory for the port (configure port port_list shared-packet-buffer command) remains available.
Note
In a SummitStack, the scheduling algorithm is automatically programmed by ExtremeXOS for the stacking links only, and might be different from the algorithm you select.
Use of all eight queues on all ports can result in insufficient buffering to sustain zero packet loss throughput during full-mesh connectivity with large packets.
When multiple QoS profiles are contending for port bandwidth and the egress traffic in each profile is within profile, the scheduler determines how the QoS profiles are serviced as described in Scheduling. In strict-priority mode, the queues are serviced based on the queue service priority value. In weighted fair-queuing mode, the queues are serviced based on the configured weight.
When configured to do so, the priority of a QoS profile can determine the 802.1p bits used in the priority field of a forwarded frame (see Introduction to Rate Limiting, Rate Shaping, and Scheduling). The priority of a QoS profile can determine the DiffServ code point value used in an IP packet when the packet is forwarded (see Replacement of DSCP on Egress).
A QoS profile change does not alter the behavior of the switch until it is assigned to a traffic group.
The egress QoS profiles on BlackDiamond X8 series switches, BlackDiamond 8900 xm-series modules, and Summit X670 series switches operate very similar to those for other BlackDiamond 8000 series modules and Summit family switches. This section describes the behaviors that are unique to the BlackDiamond 8900 xm-series modules, and the Summit X670 series switches.
The unicast and multicast queues in hardware on BlackDiamond 8900 xm-series modules, and Summit X670 series switches, are organized differently from other BlackDiamond 8000 series modules and Summit family switches.
For optimum use of the QoS profiles on these platforms, we recommend the following:
Be aware that hardware on these platforms may occasionally reorder packets within a traffic flow.
Multicast, broadcast, and flooded traffic flows for QP5-8 share a single multicast queue and are prioritized equally with the other traffic flows from QP1-8. We recommend that you do not direct multicast flows to QP5-8.
Print
this page
Email this topic
Feedback
View PDF
Download EPUB