1076 Configuring Differentiated ServicesHow Does DiffServ Functionality Vary Based on the Role of the Switch?How you configure DiffServ support in PowerConnect 8024/8024F switchsoftware varies depending on the role of the switch in your network:• Edge device: An edge device handles ingress traffic, flowing towards thecore of the network, and egress traffic, flowing away from the core. An edgedevice segregates inbound traffic into a small set of traffic classes, and isresponsible for determining a packet’s classification. Classification isprimarily based on the contents of the Layer 3 and Layer 4 headers, and isrecorded in the Differentiated Services Code Point (DSCP) added to apacket’s IP header.• Interior node: A switch in the core of the network is responsible forforwarding packets, rather than for classifying them. It decodes the DSCPin an incoming packet, and provides buffering and forwarding servicesusing the appropriate queue management algorithms.Before configuring DiffServ on PowerConnect 8024 and 8024F switches, youmust determine the QoS requirements for the network as a whole. Therequirements are expressed in terms of rules, which are used to classifyinbound or outbound traffic on a particular interface.What Are the Elements of DiffServ Configuration?During configuration, you define DiffServ rules in terms of classes, policies,and services:• Class: A class consists of a set of rules that identify which packets belongto the class. Inbound traffic is separated into traffic classes based on Layer2, Layer 3, and Layer 4 header data. The class type All is supported; thisspecifies that every match criterion defined for the class must be true for amatch to occur.• Policy: A policy defines the QoS attributes for one or more traffic classes.An attribute identifies the action taken when a packet matches a class rule.An example of an attribute is to mark a packet. The switch supports theability to assign traffic classes to output CoS queues, and to mirrorincoming packets in a traffic stream to a specific egress interface (physicalport or LAG).
