Dell PC2708, PC2748 manual General Features, Head of Line Blocking Prevention, Management Modes

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Features

General Features

Head of Line Blocking Prevention

Head of Line (HOL) blocking results in traffic delays and frame loss caused by traffic competing for the same egress port resources. HOL blocking queues packets, and the packets at the head of the queue are forwarded before packets at the end of the queue. By default, the device is configured so that the HOL blocking prevention mechanism is active at all times, except when QoS (Quality of Service), Flow Control or Back Pressure is active on a port where the HOL blocking prevention mechanism is disabled on the whole system.

Management Modes

Unmanaged Mode — Operates independent of user-configuration. The switch does not have an IP address, nor is there a web management interface and thus cannot be managed. This is the system default. From Unmanaged Mode, when the Managed Mode button is pressed, the switch enters Managed Mode with the default IP address of 192.168.2.1.

Managed Mode — Provides switch management through a web interface, and maintains the device configuration through power cycles. From Managed Mode, when the Managed Mode button is pressed, the switch enters Unmanaged Mode.

Secure Mode (PowerConnect 2748 only) — Secure Mode works by the user configuring the switch in Managed Mode and then enabling Secure Mode. Once enabled, it prevents users from making any further configuration changes to the switch. This is done by removing the IP address to the switch so that it becomes inaccessible. In Secure Mode the switch retains configuration through power cycles just like Managed Mode. To use Secure Mode, the user puts the switch in Managed Mode, configures the switch as desired, and then switches to Secure Mode via the web interface. To exit Secure Mode, the user presses the Managed Mode button. From Secure Mode when the Managed Mode button is pressed, the switch enters Managed Mode default configuration with the default IP address of 192.168.2.1.

Back Pressure Support

On half-duplex links, the receiving port prevents buffer overflows by occupying the link so that it is unavailable for additional incoming traffic. The user may enable or disable this feature on a per-port basis. The default status on all ports is set to OFF. However, this applies to links operating at Half Duplex only.

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Contents User’s Guide October Contents Using the Dell OpenManage Switch Administrator Viewing Statistics Contents Introduction System DescriptionGigabit Ethernet Ports 16 1-Gigabit Ethernet Ports 24 1-Gigabit Ethernet Ports + 2 SFP Combo ports48 1-Gigabit Ethernet Ports General Features FeaturesHead of Line Blocking Prevention Management ModesAuto Negotiation Virtual Cable Testing VCTJumbo Frames Support AutoMDI/MDIX SupportLayer 2 Features MAC Address Supported FeaturesClass of Service CoS Features Vlan Supported FeaturesPort Default Settings Ethernet Switch Management FeaturesPage Hardware Description Switch Port ConfigurationsPowerConnect 2708 Back Panel PowerConnect 2724 Back Panel PowerConnect 2748 Back Panel Power LED Physical DimensionsManaged Mode LED LED DefinitionsFan LED 2748 only Port LEDs10/100/1000BASE-T Port LEDs SFP Port LED Managed Mode ButtonCables, Port Connections, and Pinout Information Switch Ventilation Fan1000BASE-T Cable Requirements RJ-45 Connections for 10/100/1000BASE-T PortsSFP Ports Power Connectors Internal Power Supply ConnectorPin Connections for SFP Interfaces Installing the Dell PowerConnect Installation PrecautionsOverview Safety Site RequirementsUnpacking Package Contents Handling Static Sensitive DevicesUnpacking the Device Mounting the Device Installing the Device in a Rack Installing the DeviceInstalling the Device on a Wall Installing the Device on a Flat SurfaceMounting Device on a Wall Connecting the Device to AC Power SupplyBack Panel Power Connector Connecting the Device to the NetworkStarting and Configuring the Dell PowerConnect Viewing Switch OperationInitial Configuration Login Screen Click Apply Changes Page Understanding the Interface Using the Dell OpenManage Switch AdministratorInterface Components Description Using the OpenManage Switch Administrator Buttons PowerConnect Switch Management ButtonsInformation Buttons Starting the Application PowerConnect Switch Management Buttons DescriptionReset Resetting the DeviceDisplaying Configuration on Demand Configuring System Information Defining Switch InformationViewing the Switch Status Viewing System IP Address Defining Switch InformationIP Addressing Updating Static IP AddressConfiguring Dhcp Client Interface Configuration Defining Interface ConfigurationPage Configuring the Interface Open the Interface ConfigurationViewing Jumbo Frames Enabling Jumbo Frames Creating Vlan MembershipShowing/Creating VLANs Defining Vlan Interface SettingsRemoving VLANs Open the Vlan MembershipConfiguring LAG Membership Updating the Vlan Interface SettingsOpen the Vlan Interface Settings Adding a Port to a LAG Open the LAG Aggregation ConfigurationManaging System Files Downloading Files from Server Downloading Files From ServerFirmware Download File Download PowerConnect 2748 Switch ConfigurationUploading Files Configuration DownloadCopying Files Open the File Upload to ServerClick Restore Company Factory Defaults Click Apply Changes Restoring Company Factory Default SettingsAssigning Access Level User Rights Local User DatabaseOpen the Local User Database Integrated Cable Test for Copper Cables Adding a User to the Local User DatabaseDeleting a User from the Local User Database Running Integrated Cable Test Open the Integrated Cable TestClick Test Now Optical Transceivers Diagnostics Displaying Optical Transceivers Diagnostics Test ResultsOpen the Optical Transceiver Diagnostics Click show All Port MirroringAdding a Port Mirroring Session Open the Port MirroringEnabling Storm Control Configuring Storm Control on the PowerConnectConfiguring Storm Control on the PowerConnect 2716/2724 Modifying PowerConnect 2708 Storm Control Port ParametersFollowing describes Storm Control for PowerConnect Modifying PowerConnect 2748 Storm Control Port Parameters Configuring Quality of Service Quality of Service QoS OverviewVPT Tag Classification Information CoS Services Configuring QoS Settings Defining CoS SettingsMapping CoS Values to Queues Configuring the Trust ModeMapping Dscp Values to Queues Mapping a CoS value to a QueueMapping a Dscp value and assigning priority queue Page Rmon Statistics Viewing StatisticsOpen the Rmon Statistics Viewing Interface StatisticsGlossary Duplex Mode Class of ServiceBroadcast Storm Dhcp ClientFragment Flow ControlFrame Gigabit EthernetIP Address Ingress PortJumbo Frames LayerMAC Layer Managed ModeMask MulticastPage Switch Startup ConfigurationQoS RouterTrunking UnicastWildcard Mask