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Cabletron Systems 802.1Q manual Chapter Virtual Local Area Networks, DEFINING VLANs

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CHAPTER 1

VIRTUAL LOCAL AREA NETWORKS

This chapter introduces the concepts of Virtual Local Area Networks (VLANs) and discusses the central concepts of IEEE 802.1Q VLANs. This chapter also contains information on how to contact Cabletron Systems for additional support related to VLANs.

1.1DEFINING VLANs

A Virtual Local Area Network is a group of devices that function as a single Local Area Network segment (broadcast domain). The devices that make up a particular VLAN may be widely separated, both by geography and location in the network.

The creation of VLANs allows users located in separate areas or connected to separate ports to belong to a single VLAN group. Users that are assigned to such a group will send and receive broadcast and multicast trafﬁc as though they were all connected to a common network. VLAN aware switches isolate broadcast, multicast, and unknown trafﬁc received from VLAN groups, so that trafﬁc from stations in a VLAN are conﬁned to that VLAN.

When stations are assigned to a VLAN, the performance of their network connection is not changed. Stations connected to switched ports do not sacriﬁce the performance of the dedicated switched link to participate in the VLAN. As a VLAN is not a physical location, but a membership, the network switches determine VLAN membership by associating a VLAN with a particular port or frame type.

Figure 1-1shows a simple example of a port based VLAN. Two buildings house the Sales and Finance departments of a single company, and each building has its own internal network. The stations in each building connect to a SmartSwitch in the basement. The two SmartSwitches are connected to one another with a high speed link.

802.1Q VLAN User’s Guide

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Cabletron Systems 802.1Q manual Chapter Virtual Local Area Networks, DEFINING VLANs

Contents

9032599-02 802.1Q VLAN User’s GuidePage 802.1Q VLAN User’s Guide 802.1Q VLAN User’s Guide PREFACE CONTENTSCHAPTER VIRTUAL LOCAL AREA NETWORKSVLAN CONFIGURATION ContentsCHAPTER 802.1Q VLAN User’s GuideCHAPTER ContentsEXAMPLES 802.1Q VLAN User’s Guide802.1Q VLAN User’s Guide Contents802.1Q VLAN User’s Guide FIGURES802.1Q VLAN Configuration Menu Screen Menu Items TABLES802.1Q VLAN User’s Guide viiiPREFACE USING THIS GUIDESTRUCTURE OF THIS GUIDE DOCUMENT CONVENTIONS RELATED DOCUMENTS1.1 DEFINING VLANs CHAPTER VIRTUAL LOCAL AREA NETWORKSBuilding Two Building One1.2.1 802.1Q VLANs 1.2 TYPES OF VLANs1.2.2 SecureFast VLANs 1.2.3 Other VLAN Strategies1.4 VLAN TERMS 1.3 BENEFITS AND RESTRICTIONSA data frame that does not have a Tag Header Generic Attribute Registration Protocol GARP 1D TrunkGARP VLAN Registration Protocol GVRP GARP Multicast Registration Protocol GMRP1.5 GETTING HELP 802.1Q VLAN User’s Guide Chapter 1 Virtual Local Area Networks2.1 DESCRIPTION CHAPTER VLAN OPERATION2.2 VLAN COMPONENTS 2.3.1 Deﬁning a VLAN 2.3 CONFIGURATION PROCESS2.3.2 Classifying Frames to a VLAN Chapter 2 VLAN Operation2.3.3 Customizing the VLAN Forwarding List 2.4 VLAN SWITCH OPERATIONUntagged Frames 2.4.1 Receiving Frames from VLAN Ports2.4.2.1 Broadcasts, Multicasts, and Unknown Unicasts 2.4.2 Forwarding Decisions2.4.2.2 Known Unicasts Tagged Frames2.5 GARP SWITCH OPERATION 3.1 MANAGING THE SWITCH CHAPTER VLAN CONFIGURATION3.1.1 Switch Without VLANs 802.1Q Switch802.1Q Switch 3.1.2 Switch with VLANs2. Use the Port Assignment Configuration screen for the following 3.2.1 Preparing for VLAN Conﬁguration 3.2 SUMMARY OF VLAN LOCAL MANAGEMENTWhen to Use 3.3 802.1Q VLAN CONFIGURATION MENU SCREENScreen Example How to AccessFigure 3-4 802.1Q VLAN Conﬁguration Menu Screen 802.1Q VLAN Conﬁguration Menu Screen Menu Deﬁnitions802.1Q VLAN User’s Guide Table 3-1 802.1Q VLAN Conﬁguration Menu Screen Menu ItemsWhen to Use 3.4 DEVICE VLAN CONFIGURATION SCREENHow to Access Screen ExampleDevice VLAN Conﬁguration Screen Field Deﬁnitions802.1Q VLAN User’s Guide Table 3-2 Device VLAN Conﬁguration Screen Field Deﬁnitions3.4.1 Deﬁning a VLAN 3.4.3 Renaming a VLAN 3.4.2 Changing the VLAN to FID Association3.4.5 Enabling VLANs 3.4.4 Deleting a VLAN3.4.6 Disabling VLANs The default VLAN cannot be deleted from the list3.4.8 Paging Through the VLAN List 3.4.7 Changing the Forwarding ModeThe default VLAN cannot be disabled When to Use 3.5 PORT ASSIGNMENT CONFIGURATION SCREENHow to Access Screen ExampleField Deﬁnitions 3.5.1 Changing the Port Mode3.5.2 Assigning a VLAN ID 3.5.3 Paging Through the Port List 3.6 PORT FILTERING CONFIGURATION SCREENWhen to Use Screen Example How to AccessChapter 3 VLAN Conﬁguration 3-18Field Deﬁnitions 3.6.1 Displaying VLAN IDs Associated with a Port3.6.2 Selecting the Type of Filtering for a Port When to Use 3.7 VLAN FORWARDING CONFIGURATION SCREENHow to Access Screen ExampleField Deﬁnitions 3.7.1 Viewing Current VLAN PortsSee the frame format Tagged or Untagged for the frames 3.7.3 Adding Forwarding List Entries 3.7.2 Paging Through VLAN Forwarding List Entries3.7.4 Deleting Forwarding List Entries 3.7.5 Changing the Frame Format 3.8 PROTOCOL VLAN CONFIGURATION SCREENWhen to Use Screen Example How to AccessProtocol VLAN Conﬁguration Screen 802.1Q VLAN User’s GuideChapter 3 VLAN Conﬁguration Field Deﬁnitions3-26 802.1Q VLAN User’s Guide802.1Q VLAN User’s Guide Protocol VLAN Conﬁguration Screen3-27 Table 3-6 Protocol VLAN Conﬁguration Screen Field Deﬁnitions Cont’d3.8.2 Assigning a Protocol Family to a VLAN ID 3.8.1 Displaying the Current Protocol, VLAN ID, and Port AssignmentsTo see if there are VLANs currently assigned to the Protocol Protocol VLAN Conﬁguration ScreenTIP displayed in the Protocol ﬁeld, press ENTER 802.1Q VLAN User’s Guide3.8.3 Displaying the Protocol Types on Current Ports When to Use 3.9 PROTOCOL PORTS CONFIGURATION SCREENHow to Access Screen ExampleChapter 3 VLAN Conﬁguration Field Deﬁnitions3-32 802.1Q VLAN User’s Guide3.10 QUICK VLAN WALKTHROUGH 3.9.1 Adding/Deleting Ports Associated with a VLAN ID6. Use the arrow keys to highlight the ADD/DEL field It is now time to assign a port to this new VLAN Figure 3-12 Walkthrough Stage Two Figure 3-13 Walkthrough Stage Three 17. Press the SPACE bar to toggle the field to display Enabled 21. Use the arrow keys to highlight the Port field 3-40 Chapter 3 VLAN Conﬁguration802.1Q VLAN User’s Guide Figure 3-15 Final Walkthrough Stage4.1 EXAMPLE 1, SINGLE SWITCH OPERATION 802.1Q SwitchCHAPTER EXAMPLES R1 R2 R3802.1Q Switch 4.1.1 Solving the ProblemB3 B2 B1 4.1.2 Frame Handling 4.2 EXAMPLE 2, VLANS ACROSS MULTIPLE SWITCHES Figure 4-3 Example 2, VLANs Across Multiple Switches 4.2.1 Solving the ProblemSwitch 4 is set as follows Switch 2 is set as follows Figure 4-4 Bridge 1 Broadcasts Frames 4.2.2 Frame HandlingFigure 4-5 Transmitting to Switch Figure 4-6 Transmitting to Bridge 4.3 EXAMPLE 3, 1D TRUNK CONNECTION TO 802.1Q VLAN NETWORKUser B Figure 4-7 Example 3, 1D Trunk Connection to 802.1Q VLAN NetworkGreen Incorporated 4.3.1 Solving the Problem 4.3.2 Frame Handling Figure 4-8 Bridge 1 Broadcasts Frames Figure 4-10 Switch 1 Forwards to 1D Trunk Figure 4-9 Switch 2 Forwards to 1Q TrunkSwitch 1 checks the Filtering Database for the MAC address of User B. User B’s MAC address is located, and Port 2 is identified as User B’s location. The frame is then checked for eligibility and frame format for Port 2. Since Port 2 is a 1Q Trunk port, it is eligible to transmit frames for all VLANs. The frame is tagged and transmitted out Port 4.4 EXAMPLE 4, ISOLATING NETWORK TRAFFIC ACCORDING TO PROTOCOL Figure 4-11 Example 4, Isolating Trafﬁc According to Protocol 4.4.1 Solving the ProblemSwitch 3 is set as follows Switch 5 is set as follows Port 2, VLAN ID 6, Protocol AppleTalk 4-22 Chapter 4 Examples802.1Q VLAN User’s Guide Numerics INDEXIndex-2 Index802.1Q VLAN User’s Guide 802.1Q VLAN User’s Guide IndexIndex-3 Index-4 Index802.1Q VLAN User’s Guide