Juniper Networks EX2500 manual Per Hop Behavior, Assured Forwarding Drop Precedence Class

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Chapter 5: Quality of Service

Per Hop Behavior

The DSCP value determines the Per Hop Behavior (PHB) of each packet. The PHB is the forwarding treatment given to packets at each hop. QoS policies are built by the application of a set of rules to packets, based on the DSCP value, as they hop through the network.

The default settings are based on the following standard PHBs, as defined in the

IEEE standards:

Expedited Forwarding (EF)—This PHB has the highest egress priority and lowest drop precedence level. EF traffic is forwarded ahead of all other traffic. EF PHB is described in RFC 2598.

Assured Forwarding (AF)—This PHB contains four service levels, each with a different drop precedence, as shown in Table 14. Routers use drop precedence to determine which packets to discard last when the network becomes congested. AF PHB is described in RFC 2597.

Table 14: Assured Forwarding

Drop
Precedence	Class 1	Class 2	Class 3	Class 4

Low	AF11 (DSCP 10)	AF21 (DSCP 18)	AF31 (DSCP 26)	AF41 (DSCP 34)

Medium	AF12 (DSCP 12)	AF22 (DSCP 20)	AF32 (DSCP 28)	AF42 (DSCP 36)

High	AF13 (DSCP 14)	AF23 (DSCP 22)	AF33 (DSCP 30)	AF43 (DSCP 38)

Class Selector (CS)—This PHB has eight priority classes, with CS7 representing the highest priority, and CS0 representing the lowest priority, as shown in Table 15. CS PHB is described in RFC 2474.

Table 15: Class Selector

	Class
Priority	Selector	DSCP

Highest	CS7	56

	CS6	48

	CS5	40

	CS4	32

	CS3	24

	CS2	16

	CS1	8

Lowest	CS0	0

Using DSCP Values to Provide QoS 61

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Contents North Mathilda Avenue Sunnyvale, CA Configuration GuideIi „ Table of Contents Chapter VLANs Rmon Overview Rmon Group 1-Statistics Rmon Group 2-History Chapter Ports and TrunkingPort Mirroring Overview Configuring Port Mirroring AppendixesIndexes Port-Based Vlan Assignment Default Vlan SettingsPage List of Tables EX2500 Ethernet Switch Configuration Guide „ List of Tables Supported Platforms About This GuideObjectives AudienceIcon Meaning Description Documentation ConventionsList of Technical Publications Documentation FeedbackRequesting Technical Support Opening a Case with Jtac Self-Help Online Tools and ResourcesEX2500 Ethernet Switch Applications Page Configuring the Management Interface Accessing the SwitchConfigure the default gateway. Enable the gateway Dynamic Host Configuration ProtocolUsing the EX2500 Web Device Manager Using TelnetConfiguring EX2500 Web Device Manager Access via Https Configuring EX2500 Web Device Manager Access via HttpSNMPv1, SNMPv2 Using SnmpDefault Configuration User ConfigurationSNMPv3 Configure an entry in the notify table Configuring Snmp Trap HostsSNMPv1 Trap Host Configuration SNMPv2 Trap Host ConfigurationSNMPv3 Trap Host Configuration Securing Access to the SwitchConfigure the Radius secret Radius Authentication and AuthorizationHow Radius Authentication Works Configuring Radius on the SwitchRadius Authentication Features in the EX2500 Switch Radius Attributes for EX2500 User Privileges Switch User AccountsTACACS+ Authentication How TACACS+ Authentication WorksTACACS+ Authentication Features in the EX2500 Switch „ starttime „ stoptime „ elapsedtime „ disccause Command Authorization and Logging Configuring TACACS+ Authentication on the SwitchConfigure the TACACS+ secret and second secret SSH Encryption of Management Messages Configuring SSH Features on the SwitchGenerating RSA Host and Server Keys for SSH Access Secure ShellSSH Integration with Radius and TACACS+ Authentication End User Access ControlUser Access Control Considerations for Configuring End User AccountsLogging In to an End User Account Listing Current UsersVlan Overview VLANsPvid Numbers „ Port configurationVLANs and Port Vlan ID Numbers Vlan NumbersVlan Tagging Illustrates the default Vlan settings on the switchDefault Vlan Settings Port-Based Vlan Assignment Vlan Topologies and Design Considerations Vlan Configuration RulesMultiple VLANs example in is described in Table Multiple VLANs Configuration ExampleEnable tagging on uplink ports that support multiple VLANs Private Vlan Ports Private VLANsVerify the configuration Private Vlan Configuration GuidelinesPrivate Vlan Configuration Example Configure a secondary Vlan and map it to the primary VlanSpanning Tree Overview Spanning Tree ProtocolBridge Protocol Data Units BPDUs Determining the Path for Forwarding BPDUsBridge Priority Port Path Cost Spanning Tree Group Configuration GuidelinesChanging the Spanning Tree Mode Port PriorityCreating a Vlan Rules for Vlan Tagged PortsAdding and Removing Ports from STGs Port State Changes Rapid Spanning Tree ProtocolEdge Port Rstp Configuration GuidelinesRstp Configuration Example Port Type and Link TypeDefault Spanning Tree Configuration Why Do We Need Multiple Spanning Trees?Per Vlan Rapid Spanning Tree Configuring Pvrst Pvrst Configuration GuidelinesCommon Internal Spanning Tree Mstp Configuration GuidelinesMultiple Spanning Tree Protocol Mstp RegionImplementing Multiple Spanning Tree Groups Multiple Spanning Tree Groups Configuration ExampleVlan Fast Uplink ConvergenceConfiguring Fast Uplink Convergence Configuration GuidelinesPorts and Trunking Trunking OverviewStatistical Load Distribution Built-In Fault Tolerance Before Configuring Static TrunksTrunk Group Configuration Rules Port Trunk Group Configuration Example Port Trunking Configuration ExampleFollow these steps on the EX2500 switch Define a trunk group „ Destination IP DIP Configurable Trunk Hash AlgorithmLink Aggregation Control Protocol „ Destination MAC Dmac48 „ Link Aggregation Control Protocol Set the Lacp mode Lacp Configuration GuidelinesConfiguring Lacp Optionally Reducing Lacp TimeoutEx2500config-if# lacp timeout short ex2500config-if# exit QoS Overview Quality of ServiceCOS Using ACL FiltersTo delete an IP Standard ACL MAC Extended ACLsIP Standard ACLs To delete a MAC Extended ACLTo delete an IP Extended ACL IP Extended ACLsTCP/UDP Understanding ACL PriorityACL Example 1-Blocking Traffic to a Host ACL Configuration ExamplesAssigning ACLs to a Port Viewing ACL StatisticsAdd the ACL to a port ACL Example 3-Blocking Http TrafficAssign the ACLs to a port ACL Example 4-Blocking All Except Certain PacketsUsing Storm Control Filters Configuring Storm ControlBroadcast Storms Differentiated Services Concepts Using Dscp Values to Provide QoSAssured Forwarding Drop Precedence Class Per Hop BehaviorUse the following command to perform Dscp mapping QoS LevelsDscp Mapping Shows the priority bits in a VLAN-tagged packet Using 802.1p Priority to Provide QoSQueuing and Scheduling Rmon Overview Remote MonitoringRmon Group 1-Statistics Configure the Rmon statistics on a portRmon Group 2-History Configuring Rmon HistoryConfigure the Rmon History parameters for a port This configuration enables Rmon History collection on portConfigure the Rmon Alarm parameters to track Icmp messages Rmon Group 3-AlarmsAlarm MIB Objects Configuring Rmon AlarmsRmon Group 9-Events Ex2500config# rmon event 110 type log-onlyPage Igmp Snooping IgmpFastLeave IGMPv3 Snooping Igmp Snooping Configuration ExampleEx2500# show ip igmp groups Static Multicast RouterHigh Availability Overview High Availability Through Uplink Failure DetectionFailure Detection Pair Spanning Tree Protocol with UFD UFD Configuration GuidelinesMonitoring UFD UFD Configuration ExamplePage Appendixes EX2500 Ethernet Switch Configuration Guide 80 „ Appendixes Port Mirroring Overview „ Port Mirroring Overview on „ Configuring Port Mirroring onConfiguring Port Mirroring „ Index on IndexesEX2500 Ethernet Switch Configuration Guide 84 „ Indexes Numerics IndexInternet Group Management Protocol. See Igmp Management interface, configuringMulti-links between switches, port trunking Physical. See switch portsSegmentation. See IP subnets Segments. See IP subnets Quality of Service. See QoSQoS SecurityExample showing multiple VLANs Virtual Local Area Networks. See VLANs