Juniper Networks EX2500 manual Using Dscp Values to Provide QoS, Differentiated Services Concepts

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EX2500 Ethernet Switch Configuration Guide

Using DSCP Values to Provide QoS

The switch uses the Differentiated Services (DiffServ) architecture to provide QoS functions. DiffServ is described in IETF RFCs 2474 and 2475.

The six most significant bits in the ToS byte of the IP header are defined as DiffServ Code Points (DSCP). Packets are marked with a certain value depending on the type of treatment the packet must receive in the network device. DSCP is a measure of the Quality of Service (QoS) level of the packet.

The switch can classify traffic by reading the DiffServ Code Point (DSCP) or IEEE 802.1p priority value, or by using filters to match specific criteria. When network traffic attributes match those specified in a traffic pattern, the policy instructs the switch to perform specified actions on each packet that passes through it. The packets are assigned to different Class of Service (COS) queues and scheduled for transmission.

Differentiated Services Concepts

To differentiate between traffic flows, packets can be classified by their DSCP value. As shown in Figure 12, the Differentiated Services (DS) field in the IP header is an octet, and the first six bits, called the DS Code Point (DSCP), can provide QoS functions. Each packet carries its own QoS state in the DSCP. There are 64 possible DSCP values (0 through 63).

Figure 12: Layer 3 IPv4 Packet

	Version	ToS	Length	ID	Offset	TTL	Proto	FCS	SIP	DIP	Data
	Length	ToS	Length	ID	Offset	TTL	Proto	FCS	SIP	DIP	Data
	Length

Differentiated Services Code Point (DSCP)

unused

7

6

5

4

3

2

1

0

The switch can perform the following actions to the DSCP:

Read the DSCP value of ingress packets.

Map the DSCP value to a Class of Service queue (COSq). The switch can use the DSCP value to direct traffic prioritization.

With DiffServ, you can establish policies to direct traffic. A policy is a traffic-controlling mechanism that monitors the characteristics of the traffic (for example, its source, destination, and protocol), and performs a controlling action on the traffic when certain characteristics are matched.

60 Using DSCP Values to Provide QoS

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Contents Configuration Guide North Mathilda Avenue Sunnyvale, CAIi „ Table of Contents Chapter VLANs Chapter Ports and Trunking Rmon Overview Rmon Group 1-Statistics Rmon Group 2-HistoryIndexes Port Mirroring Overview Configuring Port MirroringAppendixes Default Vlan Settings Port-Based Vlan AssignmentPage List of Tables EX2500 Ethernet Switch Configuration Guide „ List of Tables Audience About This GuideObjectives Supported PlatformsDocumentation Conventions Icon Meaning DescriptionRequesting Technical Support List of Technical PublicationsDocumentation Feedback Self-Help Online Tools and Resources Opening a Case with JtacEX2500 Ethernet Switch Applications Page Accessing the Switch Configuring the Management InterfaceDynamic Host Configuration Protocol Configure the default gateway. Enable the gatewayUsing Telnet Using the EX2500 Web Device ManagerConfiguring EX2500 Web Device Manager Access via Http Configuring EX2500 Web Device Manager Access via HttpsUsing Snmp SNMPv1, SNMPv2SNMPv3 Default ConfigurationUser Configuration SNMPv2 Trap Host Configuration Configuring Snmp Trap HostsSNMPv1 Trap Host Configuration Configure an entry in the notify tableSecuring Access to the Switch SNMPv3 Trap Host ConfigurationConfiguring Radius on the Switch Radius Authentication and AuthorizationHow Radius Authentication Works Configure the Radius secretRadius Authentication Features in the EX2500 Switch Switch User Accounts Radius Attributes for EX2500 User PrivilegesTACACS+ Authentication Features in the EX2500 Switch TACACS+ AuthenticationHow TACACS+ Authentication Works „ starttime „ stoptime „ elapsedtime „ disccause Configure the TACACS+ secret and second secret Command Authorization and LoggingConfiguring TACACS+ Authentication on the Switch Secure Shell Configuring SSH Features on the SwitchGenerating RSA Host and Server Keys for SSH Access SSH Encryption of Management MessagesEnd User Access Control SSH Integration with Radius and TACACS+ AuthenticationConsiderations for Configuring End User Accounts User Access ControlListing Current Users Logging In to an End User AccountVLANs Vlan OverviewVlan Numbers „ Port configurationVLANs and Port Vlan ID Numbers Pvid NumbersIllustrates the default Vlan settings on the switch Vlan TaggingDefault Vlan Settings Port-Based Vlan Assignment Vlan Configuration Rules Vlan Topologies and Design ConsiderationsMultiple VLANs Configuration Example Multiple VLANs example in is described in TableEnable tagging on uplink ports that support multiple VLANs Private VLANs Private Vlan PortsConfigure a secondary Vlan and map it to the primary Vlan Private Vlan Configuration GuidelinesPrivate Vlan Configuration Example Verify the configurationSpanning Tree Protocol Spanning Tree OverviewBridge Priority Bridge Protocol Data Units BPDUsDetermining the Path for Forwarding BPDUs Port Priority Spanning Tree Group Configuration GuidelinesChanging the Spanning Tree Mode Port Path CostAdding and Removing Ports from STGs Creating a VlanRules for Vlan Tagged Ports Rapid Spanning Tree Protocol Port State ChangesPort Type and Link Type Rstp Configuration GuidelinesRstp Configuration Example Edge PortPer Vlan Rapid Spanning Tree Default Spanning Tree ConfigurationWhy Do We Need Multiple Spanning Trees? Pvrst Configuration Guidelines Configuring PvrstMstp Region Mstp Configuration GuidelinesMultiple Spanning Tree Protocol Common Internal Spanning TreeMultiple Spanning Tree Groups Configuration Example Implementing Multiple Spanning Tree GroupsFast Uplink Convergence VlanConfiguration Guidelines Configuring Fast Uplink ConvergenceStatistical Load Distribution Ports and TrunkingTrunking Overview Trunk Group Configuration Rules Built-In Fault ToleranceBefore Configuring Static Trunks Port Trunking Configuration Example Port Trunk Group Configuration ExampleFollow these steps on the EX2500 switch Define a trunk group „ Destination MAC Dmac Configurable Trunk Hash AlgorithmLink Aggregation Control Protocol „ Destination IP DIP48 „ Link Aggregation Control Protocol Optionally Reducing Lacp Timeout Lacp Configuration GuidelinesConfiguring Lacp Set the Lacp modeEx2500config-if# lacp timeout short ex2500config-if# exit Quality of Service QoS OverviewUsing ACL Filters COSTo delete a MAC Extended ACL MAC Extended ACLsIP Standard ACLs To delete an IP Standard ACLIP Extended ACLs To delete an IP Extended ACLUnderstanding ACL Priority TCP/UDPViewing ACL Statistics ACL Configuration ExamplesAssigning ACLs to a Port ACL Example 1-Blocking Traffic to a HostACL Example 3-Blocking Http Traffic Add the ACL to a portACL Example 4-Blocking All Except Certain Packets Assign the ACLs to a portBroadcast Storms Using Storm Control FiltersConfiguring Storm Control Using Dscp Values to Provide QoS Differentiated Services ConceptsPer Hop Behavior Assured Forwarding Drop Precedence ClassDscp Mapping Use the following command to perform Dscp mappingQoS Levels Using 802.1p Priority to Provide QoS Shows the priority bits in a VLAN-tagged packetQueuing and Scheduling Remote Monitoring Rmon OverviewConfigure the Rmon statistics on a port Rmon Group 1-StatisticsThis configuration enables Rmon History collection on port Configuring Rmon HistoryConfigure the Rmon History parameters for a port Rmon Group 2-HistoryConfiguring Rmon Alarms Rmon Group 3-AlarmsAlarm MIB Objects Configure the Rmon Alarm parameters to track Icmp messagesEx2500config# rmon event 110 type log-only Rmon Group 9-EventsPage Igmp Igmp SnoopingFastLeave Igmp Snooping Configuration Example IGMPv3 SnoopingStatic Multicast Router Ex2500# show ip igmp groupsHigh Availability Through Uplink Failure Detection High Availability OverviewSpanning Tree Protocol with UFD UFD Configuration Guidelines Failure Detection PairUFD Configuration Example Monitoring UFDPage Appendixes EX2500 Ethernet Switch Configuration Guide 80 „ Appendixes „ Port Mirroring Overview on „ Configuring Port Mirroring on Port Mirroring OverviewConfiguring Port Mirroring Indexes „ Index onEX2500 Ethernet Switch Configuration Guide 84 „ Indexes Index NumericsPhysical. See switch ports Management interface, configuringMulti-links between switches, port trunking Internet Group Management Protocol. See IgmpSecurity Quality of Service. See QoSQoS Segmentation. See IP subnets Segments. See IP subnetsVirtual Local Area Networks. See VLANs Example showing multiple VLANs