Objective

Quality of Service (QoS) is used to ensure that smooth network traffic and high priority traffic receives preferential treatment. The traffic classification is done by an Access Control List (ACL), and only traffic which meets the ACL criteria is subject to QoS classification.

QoS Basic mode allows the definition of a specific domain in the network as trusted. Within that domain, packets are marked with the VLAN Priority Tag (VPT) 802.1p value in Layer 2 and the Differentiated Service Code Point (DSCP) value for IPv4 or Traffic Class (TC) value for IPv6 in Layer 3. Nodes in this domain use these fields to assign packets to a specific output queue. It is recommended that you disable the trusted mode at the ports where the CoS/802.1p and/or DSCP values in the incoming packets are not trustworthy. Otherwise, the performance of your network may be negatively affected. This document explains how to setup the global settings on QoS Basic mode on Sx500 Series Stackable Switches.

Applicable Devices

• Sx500 Series Stackable Switches

Software Version

• 1.3.0.62

Setup Global Settings on QoS Basic Mode

Step 1. Log in to the web configuration utility to choose Quality of Service > QoS Basic Mode > Global Settings. The Global Settings page opens:

Step 2. At the Trust Mode field, click one of the values that are defined in the following:

Note: If a packet CoS level and DSCP tag are mapped to separate queues, the Trust mode determines the queue to which the packet is assigned. Also the Override Ingress DSCP field is visible, only when one of the last two options is clicked.

• CoS/802.1p — Click this option if you want the Traffic to be mapped to queues based on the VLAN Priority Tag (VPT) field in the VLAN tag, or based on the per-port default CoS/802.1p value (if there is no VLAN tag on the incoming packet). Refer the article entitled Configuration of CoS/802.1p to Queue Mapping on Sx500 Series Stackable Switchesfor further details on mapping of the DSCP to queue.

• DSCP — Click this option if you want all the IP traffic to be mapped to queues based on the Differentiated Services Code Point (DSCP) field in the IP header. Refer the article entitled Map Differentiated Services Code Point to Queue on Sx500 Series Stackable Switches for further details on mapping of the DSCP to queue. If traffic is not IP traffic, it is mapped to the best effort queue.

• CoS/802.1p-DSCP — Click this option if you want to choose either CoS/802.1p rules or DSCP rules, based upon whichever has been set.

Step 3. At the Override Ingress DSCP field, check Enable to override the original DSCP values in the incoming packets with the new values based on the DSCP Override Table.

Note: When Override Ingress DSCP is enabled, the switch uses the new DSCP values for egress queuing. It also replaces the original DSCP values in the packets with the new DSCP values.

Step 4. If Override Ingress DSCP is enabled, click DSCP Override Table to reconfigure DSCP. The DSCP Override window appears.

Step 5. Choose the appropriate DSCP value from the drop-down list. The values are in the range of 0 to 63. These values are dependent upon the configuration of service providers. Typically the higher the DSCP value, the higher the priority.

• DSCP In — This column displays the DSCP value of the incoming packet that needs to be mapped to an alternative value.

• DSCP Out — Choose an option to indicate mapping of the outgoing value. By default, the DSCP In and DSCP Out are the same.

Step 6. Click Apply to save the changes in the DSCP Override Table.

Step 7. Click Apply to save the changes in the Global Settings page. The Running Configuration file is updated with the new DSCP values.