Cabletron Systems 802.1Q manual Forwarding Decisions, Broadcasts, Multicasts, and Unknown Unicasts

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VLAN Switch Operation

The switch will now make a forwarding decision on the frame, as described in Section 2.4.2, Forwarding Decisions.

Tagged Frames

In this example, the switch receives a tagged frame from Port 4. The switch examines the frame and notices the frame is tagged for VLAN C. This frame may have already been through a VLAN aware switch, or originated from a station capable of specifying a VLAN membership. If a switch receives a frame containing a tag, the switch will classify the frame in regard to its tag rather than the PVID for its port.

The switch will now make a forwarding decision on the frame, as described in Section 2.4.2, Forwarding Decisions.

2.4.2Forwarding Decisions

The type of frame under consideration and the filter setting of a VLAN switch determines how it forwards VLAN frames.

2.4.2.1Broadcasts, Multicasts, and Unknown Unicasts

If a frame with a broadcast, multicast, or other unknown address is received by an 802.1Q VLAN aware switch, the switch checks the VLAN classification of the frame. The switch then forwards the frame out all ports that are identified in the Forwarding List for that VLAN. For example, if Port 3, shown in Figure 2-1, received the frame, the frame would then be sent to all ports that had VLAN C in their Port VLAN List.

2.4.2.2Known Unicasts

When a VLAN switch receives a frame with a known MAC address as its destination address, the action taken by the switch to determine how the frame is transmitted depends on the VLAN, the VLAN associated FID, and if the port identified to send the frame is enabled to do so.

When a frame is received it is classified into a VLAN. The destination address is looked up in the FID associated with the VLAN. If a match is found, it is forwarded out the port identified in the lookup if, and only if, that port is allowed to transmit frames for that VLAN. If a match is not found, then the frame is flooded out all ports that are allowed to transmit frames belonging to that VLAN.

802.1Q VLAN User’s Guide

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Contents 802.1Q Vlan User’s Guide Page 802.1Q Vlan User’s Guide 802.1Q Vlan User’s Guide Contents Contents Contents Contents 802.1Q Vlan User’s Guide Figures Tables Structure of this Guide Using this GuideDocument Conventions Related DocumentsDefining VLANs Chapter Virtual Local Area NetworksBuilding One Building Two 1 802.1Q VLANs Types of VLANsSecureFast VLANs Other Vlan StrategiesVlan Terms Benefits and RestrictionsData frame that does not have a Tag Header 1D Trunk Your email address Getting Help802.1Q Vlan User’s Guide Vlan Components Description1 Defining a Vlan Configuration ProcessClassifying Frames to a Vlan Customizing the Vlan Forwarding List Vlan Switch OperationReceiving Frames from Vlan Ports Inside the SwitchBroadcasts, Multicasts, and Unknown Unicasts Forwarding DecisionsKnown Unicasts Garp Switch Operation Switch Without VLANs Managing the SwitchSwitch Management with VLANs Switch with VLANsManaging the Switch Preparing for Vlan Configuration Summary of Vlan Local ManagementWhen to Use 802.1Q Vlan Configuration Menu ScreenHow to Access Menu Definitions Device Vlan Configuration Screen Device Vlan Configuration ScreenField Definitions 1 Defining a Vlan Renaming a Vlan Changing the Vlan to FID AssociationEnabling VLANs Deleting a VlanDisabling VLANs Paging Through the Vlan List Changing the Forwarding ModePort Assignment Configuration Screen Port Assignment Configuration ScreenPort Mode Changing the Port ModeAssigning a Vlan ID Paging Through the Port List Port Filtering Configuration ScreenPort Filtering Configuration Screen Vlan Lists Displaying Vlan IDs Associated with a PortSelecting the Type of Filtering for a Port Vlan Forwarding Configuration Screen Vlan Forwarding Configuration ScreenFrame Format Viewing Current Vlan PortsAdding Forwarding List Entries Paging Through Vlan Forwarding List EntriesDeleting Forwarding List Entries Changing the Frame Format Protocol Vlan Configuration ScreenProtocol Vlan Configuration Screen Selectable Feature Status Ether type Assigning a Protocol Family to a Vlan IDProtocol Vlan Configuration Screen Displaying the Protocol Types on Current Ports 10 Protocol Ports Configuration Screen Protocol Ports Configuration ScreenDelete ALL Quick Vlan Walkthrough Adding/Deleting Ports Associated with a Vlan ID802.1Q Vlan User’s Guide Hybrid 12 Walkthrough Stage Two 13 Walkthrough Stage Three 14 Walkthrough Stage Four Quick Vlan Walkthrough 15 Final Walkthrough Stage Chapter Examples Example 1, Single Switch OperationSwitch Configured for VLANs Solving the ProblemFrame Handling Example 2, Vlans Across Multiple Switches Example 2, VLANs Across Multiple Switches Switch Example 2, VLANs Across Multiple Switches Bridge 1 Broadcasts Frames Transmitting to Switch Transmitting to Bridge Example 3, 1D Trunk Connection to 802.1Q Vlan NetworkExample 3, 1D Trunk Connection to 802.1Q Vlan Network Solving the Problem Frame Handling 226318 Switch 2 Forwards to 1Q Trunk Examples Example 4, Isolating Network Traffic According to Protocol 11 Example 4, Isolating Traffic According to Protocol Switch Examples Example 4, Isolating Network Traffic According to Protocol Examples 802.1Q Vlan User’s Guide Numerics IndexIndex-2 802.1Q Vlan User’s Guide 802.1Q Vlan User’s Guide Index-3 Index Index-4 802.1Q Vlan User’s Guide
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