Juniper Networks EX2500 manual Using 802.1p Priority to Provide QoS

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Chapter 5: Quality of Service

Using 802.1p Priority to Provide QoS

The EX2500 switch provides Quality of Service (QoS) functions based on the priority bits in a packet’s VLAN header. (The priority bits are defined by the 802.1p standard within the IEEE 802.1Q VLAN header.) The 802.1p bits, if present in the packet, specify the priority that should be given to packets during forwarding. Packets with a numerically higher (non-zero) priority are given forwarding preference over packets with lower priority value.

The IEEE 802.1p standard uses eight levels of priority (0 through 7). Priority 7 is assigned to highest-priority network traffic, such as OSPF or RIP routing table updates, priorities 5 through 6 are assigned to delay-sensitive applications such as voice and video, and lower priorities are assigned to standard applications. A value of 0 (zero) indicates a “best effort” traffic prioritization, and this is the default when traffic priority has not been configured on your network. The switch can filter packets based on the 802.1p values.

Figure 13 shows the priority bits in a VLAN-tagged packet.

Figure 13: Layer 2 802.1q/802.1p VLAN-Tagged Packet

Preamble

SFD

DMAC SMAC

Tag

E Type

Data

FCS


		Priority															VLAN				Identifier					(VID)

7		6		5		4		3		2			1			0	7			6			5				4			3				2				1				0

Ingress packets receive a priority value, as follows:

Tagged packets—The switch reads the 802.1p priority in the VLAN tag.

Untagged packets—The switch tags the packet and assigns an 802.1p priority value, based on the port’s default 802.1p priority.

Egress packets are placed in a Class of Service (COS) queue based on the priority value, and scheduled for transmission based on the COS queue number. Higher COS queue numbers provide forwarding precedence.

The following is an example of 802.1p configuration:

1.Configure a port’s default 802.1p priority value to 2.

ex2500(config)# interface port 1 ex2500(config-if)# dot1p 2 ex2500(config-if)# exit

2.Map the 802.1p priority value to a COS queue. ex2500(config)# qos transmit-queue mapping 1 0

Using 802.1p Priority to Provide QoS 63

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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 TrunkingIndexes Port Mirroring Overview Configuring Port MirroringAppendixes Port-Based Vlan Assignment Default Vlan SettingsPage List of Tables EX2500 Ethernet Switch Configuration Guide „ List of Tables Objectives About This GuideAudience Supported PlatformsIcon Meaning Description Documentation ConventionsRequesting Technical Support List of Technical PublicationsDocumentation Feedback 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 SnmpSNMPv3 Default ConfigurationUser Configuration SNMPv1 Trap Host Configuration Configuring Snmp Trap HostsSNMPv2 Trap Host Configuration Configure an entry in the notify tableSNMPv3 Trap Host Configuration Securing Access to the SwitchHow Radius Authentication Works Radius Authentication and AuthorizationConfiguring Radius on the Switch Configure the Radius secretRadius Authentication Features in the EX2500 Switch Radius Attributes for EX2500 User Privileges Switch User AccountsTACACS+ 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 Generating RSA Host and Server Keys for SSH Access Configuring SSH Features on the SwitchSecure Shell SSH Encryption of Management MessagesSSH 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 VLANsVLANs and Port Vlan ID Numbers „ Port configurationVlan Numbers Pvid 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 VLANsPrivate Vlan Configuration Example Private Vlan Configuration GuidelinesConfigure a secondary Vlan and map it to the primary Vlan Verify the configurationSpanning Tree Overview Spanning Tree ProtocolBridge Priority Bridge Protocol Data Units BPDUsDetermining the Path for Forwarding BPDUs Changing the Spanning Tree Mode Spanning Tree Group Configuration GuidelinesPort Priority Port Path CostAdding and Removing Ports from STGs Creating a VlanRules for Vlan Tagged Ports Port State Changes Rapid Spanning Tree ProtocolRstp Configuration Example Rstp Configuration GuidelinesPort Type and Link Type Edge PortPer Vlan Rapid Spanning Tree Default Spanning Tree ConfigurationWhy Do We Need Multiple Spanning Trees? Configuring Pvrst Pvrst Configuration GuidelinesMultiple Spanning Tree Protocol Mstp Configuration GuidelinesMstp Region Common Internal Spanning TreeImplementing Multiple Spanning Tree Groups Multiple Spanning Tree Groups Configuration ExampleVlan Fast Uplink ConvergenceConfiguring Fast Uplink Convergence Configuration GuidelinesStatistical Load Distribution Ports and TrunkingTrunking Overview Trunk Group Configuration Rules Built-In Fault ToleranceBefore Configuring Static Trunks Port Trunk Group Configuration Example Port Trunking Configuration ExampleFollow these steps on the EX2500 switch Define a trunk group Link Aggregation Control Protocol Configurable Trunk Hash Algorithm„ Destination MAC Dmac „ Destination IP DIP48 „ Link Aggregation Control Protocol Configuring Lacp Lacp Configuration GuidelinesOptionally Reducing Lacp Timeout Set the Lacp modeEx2500config-if# lacp timeout short ex2500config-if# exit QoS Overview Quality of ServiceCOS Using ACL FiltersIP Standard ACLs MAC Extended ACLsTo delete a MAC Extended ACL To delete an IP Standard ACLTo delete an IP Extended ACL IP Extended ACLsTCP/UDP Understanding ACL PriorityAssigning ACLs to a Port ACL Configuration ExamplesViewing ACL Statistics ACL Example 1-Blocking Traffic to a HostAdd the ACL to a port ACL Example 3-Blocking Http TrafficAssign the ACLs to a port ACL Example 4-Blocking All Except Certain PacketsBroadcast Storms Using Storm Control FiltersConfiguring Storm Control Differentiated Services Concepts Using Dscp Values to Provide QoSAssured Forwarding Drop Precedence Class Per Hop BehaviorDscp Mapping Use the following command to perform Dscp mappingQoS Levels 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 portConfigure the Rmon History parameters for a port Configuring Rmon HistoryThis configuration enables Rmon History collection on port Rmon Group 2-HistoryAlarm MIB Objects Rmon Group 3-AlarmsConfiguring Rmon Alarms Configure the Rmon Alarm parameters to track Icmp messagesRmon 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 IndexMulti-links between switches, port trunking Management interface, configuringPhysical. See switch ports Internet Group Management Protocol. See IgmpQoS Quality of Service. See QoSSecurity Segmentation. See IP subnets Segments. See IP subnetsExample showing multiple VLANs Virtual Local Area Networks. See VLANs