Enterasys Networks 802.1Q User Manual
802.1Q VLAN
User’s Guide
9032599-03
NOTICE
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whether any such changes have been made.
The hardware, firmware, or software described in this document is subject to change without notice.
IN NO EVENT SHALL ENTERASYS NETWORKS BE LIABLE FOR ANY INCIDENTAL, INDIRECT, SPECIAL,
OR CONSEQUENTIAL DAMAGES WHATSOEVER (INCLUDING BUT NOT LIMITED TO LOST PROFITS)
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2002 Enterasys Networks, Inc. All rights reserved.
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Order Number: 9032599-03 December 2002
LANVIEW is a registered trademark and Enterasys Networks, NETSIGHT, MATRIX, WEBVIEW, and any logos
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All other product names mentioned in this manual may be trademarks or registered trademarks of their respective
companies.
Version: Information in this guide refers to firmware version 3.x and 4.x only.
It does not refer to firmware version 5.x.
This guide applies to 2X2XX, 6X2XX, and 6X3XX Ethernet switch
devices only.
Contents
Figures ............................................................................................................................................ v
Tables..............................................................................................................................................vi
PREFACE
Using This Guide............................................................................................................vii
Structure of This Guide .................................................................................................. vii
Related Documents....................................................................................................... viii
Document Conventions................................................................................................. viii
1
2
3
1.1 Defining VLANs............................................................................................... 1-1
1.2 Types of VLANs .............................................................................................. 1-2
1.2.1 802.1Q VLANs ................................................................................ 1-3
1.2.2 SecureFast VLANs ......................................................................... 1-3
1.2.3 Other VLAN Strategies ................................................................... 1-3
1.3 Benefits and Restrictions ................................................................................ 1-3
1.4 VLAN Terms.................................................................................................... 1-4
1.5 Getting Help .................................................................................................... 1-6
2.1 Description ...................................................................................................... 2-1
2.2 VLAN Components ......................................................................................... 2-1
2.3 Configuration Process..................................................................................... 2-2
2.3.1 Defining a VLAN ............................................................................. 2-2
2.3.2 Classifying Frames to a VLAN ........................................................ 2-2
2.3.3 Customizing the VLAN Forwarding List .......................................... 2-2
2.4 VLAN Switch Operation .................................................................................. 2-3
2.4.1 Receiving Frames from VLAN Ports ............................................... 2-4
2.4.2 Forwarding Decisions ..................................................................... 2-4
2.4.2.1 Broadcasts, Multicasts, and Unknown Unicasts.............. 2-4
2.4.2.2 Known Unicasts............................................................... 2-5
2.5 GARP Switch Operation.................................................................................. 2-5
3.1 Managing the Switch....................................................................................... 3-1
3.1.1 Switch Without VLANs .................................................................... 3-1
3.1.2 Switch with VLANs.......................................................................... 3-2
3.2 Summary of VLAN Local Management........................................................... 3-4
3.3 802.1Q VLAN Configuration Menu Screen ..................................................... 3-5
3.4 Device VLAN Configuration Screen ................................................................ 3-7
Contents iii
3.4.1 Defining a VLAN ........................................................................... 3-10
3.4.2 Changing the VLAN to FID Association ........................................ 3-11
3.4.3 Renaming a VLAN ........................................................................ 3-11
3.4.4 Deleting a VLAN ........................................................................... 3-12
3.4.5 Enabling VLANs............................................................................ 3-12
3.4.6 Disabling VLANs ........................................................................... 3-12
3.4.7 Changing the Forwarding Mode.................................................... 3-13
3.4.8 Paging Through the VLAN List ..................................................... 3-13
3.5 Port Assignment Configuration Screen ......................................................... 3-14
3.5.1 Changing the Port Mode ............................................................... 3-15
3.5.2 Assigning a VLAN ID .................................................................... 3-16
3.5.3 Paging Through the Port List ........................................................ 3-17
3.6 Port Filtering Configuration Screen ............................................................... 3-17
3.6.1 Displaying VLAN IDs Associated with a Port ................................ 3-19
3.6.2 Selecting the Type of Filtering for a Port....................................... 3-20
3.7 VLAN Forwarding Configuration Screen ....................................................... 3-20
3.7.1 Viewing Current VLAN Ports......................................................... 3-22
3.7.2 Paging Through VLAN Forwarding List Entries ............................ 3-22
3.7.3 Adding Forwarding List Entries ..................................................... 3-22
3.7.4 Deleting Forwarding List Entries ................................................... 3-23
3.7.5 Changing the Frame Format ......................................................... 3-23
3.8 Protocol VLAN Configuration Screen............................................................ 3-24
3.8.1 Displaying the Current Protocol, VLAN ID, and
Port Assignments.......................................................................... 3-27
3.8.2 Assigning a Protocol Family to a VLAN ID.................................... 3-27
3.8.3 Displaying the Protocol Types on Current Ports ........................... 3-29
3.9 Protocol Ports Configuration Screen............................................................. 3-29
3.9.1 Adding/Deleting Ports Associated with a VLAN ID .......................3-31
3.10 Quick VLAN Walkthrough ............................................................................. 3-32
4
iv Contents
4.1 Example 1, Single Switch Operation ............................................................... 4-1
4.2 Example 2, VLANs Across Multiple Switches ................................................. 4-3
4.3 Example 3, 1D Trunk Connection to 802.1Q VLAN Network .......................... 4-8
4.4 Example 4, Isolating Network Traffic According to Protocol ......................... 4-14
4.1.1 Solving the Problem........................................................................ 4-2
4.1.2 Frame Handling .............................................................................. 4-3
4.2.1 Solving the Problem........................................................................ 4-4
4.2.2 Frame Handling .............................................................................. 4-6
4.3.1 Solving the Problem...................................................................... 4-10
4.3.2 Frame Handling ............................................................................ 4-11
4.4.1 Solving the Problem...................................................................... 4-15
Figures
Figure Page
1-1 Example of a VLAN ......................................................................................................... 1-2
2-1 Inside the Switch ............................................................................................................. 2-3
3-1 Switch Management with Only Default VLAN ................................................................. 3-2
3-2 Switch Management with VLANs .................................................................................... 3-3
3-3 802.1Q VLAN Screen Hierarchy ..................................................................................... 3-4
3-4 802.1Q VLAN Configuration Menu Screen ..................................................................... 3-6
3-5 Device VLAN Configuration Screen ................................................................................ 3-8
3-6 Port Assignment Configuration Screen ......................................................................... 3-14
3-7 Port Filtering Configuration Screen ............................................................................... 3-18
3-8 VLAN Forwarding Configuration Screen ....................................................................... 3-21
3-9 Protocol VLAN Configuration Screen ............................................................................ 3-24
3-10 Protocol Ports Configuration Screen ............................................................................. 3-30
3-11 Walkthrough Stage One ................................................................................................ 3-33
3-12 Walkthrough Stage Two ................................................................................................ 3-34
3-13 Walkthrough Stage Three ............................................................................................. 3-35
3-14 Walkthrough Stage Four ............................................................................................... 3-36
3-15 Final Walkthrough Stage ............................................................................................... 3-37
4-1 Example 1, Single Switch Operation ............................................................................... 4-1
4-2 Switch Configured for VLANs.......................................................................................... 4-2
4-3 Example 2, VLANs Across Multiple Switches ................................................................. 4-4
4-4 Bridge 1 Broadcasts Frames........................................................................................... 4-6
4-5 Transmitting to Switch 4 .................................................................................................. 4-7
4-6 Transmitting to Bridge 4 .................................................................................................. 4-8
4-7 Example 3, 1D Trunk Connection to 802.1Q VLAN Network .......................................... 4-9
4-8 Bridge 1 Broadcasts Frames......................................................................................... 4-12
4-9 Switch 2 Forwards to 1Q Trunk.....................................................................................4-12
4-10 Switch 1 Forwards to 1D Trunk ..................................................................................... 4-13
4-11 Example 4, Isolating Traffic According to Protocol ........................................................ 4-15
Figures v
Tables
Ta bl e Page
3-1 802.1Q VLAN Configuration Menu Screen Menu Items ...............................................3-6
3-2 Device VLAN Configuration Screen Field Definitions ...................................................3-9
3-3 Port Assignment Configuration Screen Field Definitions ............................................3-15
3-4 Port Filtering Configuration Screen Field Definitions ..................................................3-18
3-5 VLAN Forwarding Configuration Screen Field Definitions ..........................................3-21
3-6 Protocol VLAN Configuration Screen Field Definitions ...............................................3-25
3-7 Protocol Ports Configuration Screen Field Definitions ................................................3-30
vi
Preface
Welcome to the Enterasys Networks 802.1Q VLAN User’s Guide. This guide introduces and
describes Enterasys Networks’ implementation of the IEEE 802.1Q standard for 802.1Q Virtual
Local Area Network (VLAN) technology, and the VLAN Local Management screens used to
configure Enterasys Networks products used in 802.1Q VLAN environments.
IMPORTANT NOTICE
Information in this guide refers to firmware version 3.x and 4.x only. It does not refer to firmware
version 5.x.
This guide applies to 2X2XX, 6X2XX, and 6X3XX Ethernet switch devices only.
USING THIS GUIDE
This guide serves as a supplement to the Local Management chapter of the Enterasys Networks
user’s guides for devices that support 802.1Q VLANs. Read Chapter 1 and Chapter 2 first to gain
an understanding of VLANs, the associated terminology, and the process for configuring VLANs
on a switch. Look at the examples in Chapter 4 to see how VLANs can be created and changed
using the existing network infrastructure in a building and how the switch handles the frames while
they make their way through the networks shown in the examples. Chapter 3 describes the VLAN
Local Management screens and provides a quick walkthrough on how to use them to configure
VLANs in a switch.
STRUCTURE OF THIS GUIDE
This guide is organized as follows:
Chapter 1, Virtual Local Area Networks, presents the basic concepts of VLANs, including their
benefits and uses. This chapter also provides information about how to obtain additional help if
needed.
Chapter 2, VLAN Operation, describes the operation of an 802.1Q VLAN, the steps necessary to
prepare an 802.1Q VLAN aware switch for VLAN operation, and examines the operation of an
802.1Q VLAN switch.
Preface vii
Related Documents
Chapter 3, VLAN Configuration, describes how to set up the switch for local and remote
management, shows the Local Management screens used in 802.1Q VLAN configuration and
explains their use.
Chapter 4, Examples, offers examples of 802.1Q VLANs and explains how network transmissions
are treated by the components of each VLAN.
RELATED DOCUMENTS
Other Enterasys Networks documents that may be useful for understanding some of the concepts
introduced or discussed in this guide are listed below:
The SmartSwitch user’s guide of any Enterasys Networks 802.1Q VLAN aware SmartSwitch
device.
The manual can be obtained from the World Wide Web in Adobe Acrobat Portable Document
Format (PDF) at the following site:
http://www.enterasys.com/
DOCUMENT CONVENTIONS
The following conventions are used throughout this document:
Note symbol. Calls the reader’s attention to any item of information that may be of
special importance.
In Local Management sections, Bold type indicates fields, field values, and commands that can be
highlighted or selected by the user.
In Local Management sections, keystrokes are shown in UPPERCASE.
Italic type denotes complete book titles.
viii Preface
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 Enterasys Networks for additional support related to VLANs.
1.1 DEFINING 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 1-1 shows 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.
Virtual Local Area Networks 1-1
Types of VLANs
Building One Building Two
SS
S
FF
A
SmartSwitch SmartSwitch
S
Member of Sales Network
10
9
1
trunk
8
F
Member of Finance Network
SSS
FF
7
6
B
2263-01
Figure 1-1 Example of a VLAN
In this example, the Sales and Finance workstations have been placed on two separate VLANs. In
a plain Ethernet environment, the entire network is a broadcast domain, and the SmartSwitches
follow the IEEE 802.1D bridging specification to send data between stations. A broadcast or
multicast transmission from a Sales workstation in Building One would propagate to all the switch
ports on SmartSwitch A, cross the high speed link to SmartSwitch B, and then propagated out all
switch ports on SmartSwitch B. The SmartSwitches treat each port as being equivalent to any other
port, and have no understanding of the departmental memberships of each workstation.
In a VLAN environment, each SmartSwitch understands that certain individual ports or frames are
members of separate workgroups. In this environment, a broadcast or multicast data transmission
from one of the Sales stations in Building One would reach SmartSwitch A, be sent to the ports
connected to other local members of the Sales VLAN, cross the high speed link to SmartSwitch B,
and then be sent to any other ports and workstations on SmartSwitch B that are members of the
Sales VLAN.
1.2 TYPES OF VLANs
There are a number of different strategies for creating Virtual Local Area Networks, each with
their own approaches to defining a station’s membership in a particular VLAN.
1-2 Virtual Local Area Networks
Benefits and Restrictions
1.2.1 802.1Q VLANs
An 802.1Q VLAN switch determines the VLAN membership of a data frame by its Tag Header,
described later in this chapter. If the frame received is not tagged, the switch classifies the frame
into the VLAN that is assigned as the default VLAN of the switch.
Some or all ports on the switch may be configured to operate as GARP VLAN Registration
Protocol (GVRP) ports. If a frame received is tagged, the frame is forwarded to the GVRP ports
that are configured to transmit frames associated with the frame VLAN ID and protocol. If the
received frame is not tagged, the frame is examined and tagged as belonging to the default VLAN.
Then the frame is forwarded to the GVRP ports that are configured to transmit frames associated
with the default VLAN and the frame protocol.
1.2.2 SecureFast VLANs
Enterasys Networks’ SecureFast VLAN strategy takes a different approach to creating virtual
LANs. In a SecureFast VLAN environment, the switches in the network recognize Network Layer
routing requests and translate them. Based on this translation, the switches set up a connection
between the end devices in the network.
1.2.3 Other VLAN Strategies
VLANs may also be created by a variety of addressing schemes, including the recognition of
groups of MAC addresses or types of traffic. One of the best-known VLAN-like schemes is the use
of IP Subnets to divide networks into smaller subnetworks.
1.3 BENEFITS AND RESTRICTIONS
The primary benefit of the 802.1Q VLAN technology is that it provides localization of traffic. This
function also offers improvements in security and performance to stations assigned to a VLAN.
While the localization of traffic to VLANs can improve security and performance, it imposes some
restrictions on network devices that participate in the VLAN. Through the use of Filtering
Database ID’s (FIDs) security can be implemented to enable or prevent users from one or more
VLANs from communicating with each other.
One or more VLANs can be assigned to a FID so that all the users that share a common FID can
communicate with each other regardless of their VLAN affiliation. However, for the sake of
security, the members of one FID cannot communicate with the members of another FID.
To set up a VLAN, all the network switch devices that are assigned to the VLAN must support the
IEEE 802.1Q specification for VLANs. Before you attempt to implement a VLAN strategy, ensure
that the switches under consideration support the IEEE 802.1Q specification.
Virtual Local Area Networks 1-3
VLAN Terms
1.4 VLAN TERMS
To fully understand the operation and configuration of port based VLANs, it is essential to
understand the definitions of several key terms.
VLAN ID
A unique number (between 1 and 4094) that identifies a particular VLAN.
VLAN Name
A 32-character alphanumeric name associated with a VLAN ID. The VLAN Name is intended to
make user-defined VLANs easier to identify and remember.
Filtering Database Identifier (FID)
Addressing information that the device learns about a VLAN is stored in the filtering database
assigned to that VLAN. Several VLANs can be assigned to the same FID to allow those VLANs to
share addressing information. This enables the devices in the different VLANs to communicate
with each other when the individual ports have been configured to allow communication to occur.
The configuration is accomplished using the Local Management VLAN Forwarding Configuration
screen. By default a VLAN is assigned to the FID that matches its VLAN ID.
Tag Header (VLAN Tag)
Four bytes of data inserted in a frame that identifies the VLAN/frame classification. The Tag
Header is inserted into the frame directly after the Source MAC address field. Twelve bits of the
Tag Header represent the VLAN ID. The remaining bits are other control information.
Tagged Frame
A data frame that contains a Tag Header. A VLAN aware device can add the Tag Header to any
frame it transmits.
Untagged Frame
A data frame that does not have a Tag Header.
Default VLAN
The VLAN to which all ports are assigned upon initialization. The Default VLAN has a VLAN ID
of 1 and cannot be deleted or renamed.
Forwarding List
A list of the ports on a particular device that are eligible to transmit frames for a selected VLAN.
1-4 Virtual Local Area Networks
VLAN Terms
Port VLAN List
A per port list of all eligible VLANs whose frames can be forwarded out one specific port and the
frame format (tagged or untagged) of transmissions for that port. The Port VLAN List specifies
what VLANs are associated with a single port for frame transmission purposes.
Filtering Database
A database structure within the switch that keeps track of the associations between MAC
addresses, VLANs, and interface (port) numbers. The Filtering Database is referred to when a
switch makes a forwarding decision on a frame.
1Q Trunk
A connection between 802.1Q switches that passes only traffic with a VLAN Tag Header inserted
in the frame. By default, a port designated as a 1Q Trunk port has all VLANs in its Port VLAN
List and is configured to transmit all frames as tagged frames. A 1Q Trunk drops all incoming
frames that do not have a VLAN tag.
1D Trunk
A connection from a switch that passes only untagged traffic. By default, a port designated as a 1D
Trunk port has all VLANs on its Port VLAN List and is configured to transmit all frames as
untagged frames.
Generic Attribute Registration Protocol (GARP)
GARP is a protocol used to propagate state information throughout a switched network.
GARP VLAN Registration Protocol (GVRP)
A GARP application used to dynamically create VLANs across a switched network.
GARP Multicast Registration Protocol (GMRP)
A GARP application that functions in a similar fashion as GVRP, except that GMRP registers
multicast addresses on ports to control the flooding of multicast frames.
Virtual Local Area Networks 1-5
Getting Help
1.5 GETTING HELP
For additional support related to this document, contact Enterasys Networks using one of the
following methods:
World Wide Web http://www.enterasys.com
Phone (603) 332-9400
Internet mail support@enterasys.com
FTP ftp://ftp.enterasys.com
Login anonymous
Password your email address
To send comments or suggestions concerning this document, contact the Technical Writing
Department via the following email address: TechWriting@enterasys.com
Make sure to include the document Part Number in the email message.
Before contacting Enterasys Networks for technical support, have the following information
ready:
• Your Enterasys Networks service contract number
• A description of the failure
• A description of any action(s) already taken to resolve the problem (e.g., changing mode
switches, rebooting the unit, etc.)
• The serial and revision numbers of all involved Enterasys Networks products in the network
• A description of your network environment (layout, cable type, etc.)
• Network load and frame size at the time of trouble (if known)
• The device history (i.e., have you returned the device before, is this a recurring problem, etc.)
• Any previous Return Material Authorization (RMA) numbers
1-6 Virtual Local Area Networks
2
VLAN Operation
This chapter describes the operation of a VLAN switch and discusses the operations that a VLAN
switch performs in response to both normal and VLAN-originated network traffic.
2.1 DESCRIPTION
The 802.1Q VLAN operation is slightly different than the operation of traditional switched
networking systems. These differences are due to the importance of keeping track of each frame
and its VLAN association as it passes from switch to switch or from port to port within a switch.
2.2 VLAN COMPONENTS
Before describing the operation of an 802.1Q VLAN, it is important to understand the basic
elements that are combined to make up an 802.1Q VLAN.
Stations
A station is any end unit that belongs to a network. In the vast majority of cases, stations are the
computers through which the users access the network.
Switches
In order to configure a group of stations into a VLAN, the stations must be connected to VLAN
aware switches. It is the job of the switch to classify received frames into VLAN memberships and
transmit frames, according to VLAN membership, with or without a VLAN Tag Header.
VLAN Operation 2-1
Configuration Process
2.3 CONFIGURATION PROCESS
Before a VLAN can operate, steps must be performed to configure the switch to establish and
configure a VLAN. Enterasys Networks VLAN aware SmartSwitches default to operate in the
802.1Q VLAN mode. However, further configuration is necessary to establish multiple logical
networks.
NOTE: The actual steps involved in VLAN configuration using Local Management are
presented in Chapter 3, VLAN Configuration.This brief section describes the actions
that must be taken in very general terms, and is intended only to aid in the
Administrator’s understanding of VLAN switch operation.
2.3.1 Defining a VLAN
A VLAN must exist and have a unique identity before any ports or rules can be assigned to it. The
Administrator defines a VLAN by assigning it a unique identification number (the VLAN ID), a
filter database association, and an optional name. The VLAN ID is the number that will identify
data frames originating from, and intended for, the ports that will belong to this new VLAN.
2.3.2 Classifying Frames to a VLAN
Now that a VLAN has been created, rules are defined to classify all frames in a VLAN. This is
accomplished through management by associating a VLAN ID with each port on the switch.
Optionally, frames can be classified according to a protocol identifier contained within the frame.
The order of frame classification priority is by VLAN Tag, a protocol match, and lastly the PVID.
This combination of the switch port’s identification and the VLAN ID becomes the Port VLAN ID
(PVID).
At the same time, the Administrator configures the trunk ports that need to consider themselves
members of every VLAN. The configuration of trunk ports is very important in multiswitch VLAN
configurations where a frame’s VLAN membership needs to be maintained across several
switches.
2.3.3 Customizing the VLAN Forwarding List
Each port on a VLAN aware switch has a VLAN forwarding list that contains, as a minimum, the
PVID of the VLAN configured. Additionally, the Port VLAN Forwarding List of each port can be
configured to allow any number of VLANs to be added to its list. In the case of GMRP (dynamic
VLANs), the list can have VLANs added and deleted by the switch as directed by the protocol.
2-2 VLAN Operation
VLAN Switch Operation
2.4 VLAN SWITCH OPERATION
IEEE 802.1Q VLAN switches act on the classification of frames into VLANs. Sometimes, VLAN
classification is based on tags in the headers of data frames. These VLAN tags are added to data
frames by the switch as the frames are transmitted out certain ports, and are later used to make
forwarding decisions by the switch and other VLAN aware switches. In the absence of a VLAN
tag header, the classification of a frame into a particular VLAN depends upon the configuration of
the switch port that received the frame.
The operation of an 802.1Q VLAN switch is best understood from a point of view of the switch
itself. To illustrate this concept, the examples that follow view the switch operations from inside
the switch.
Figure 2-1 depicts the inside of a switch with six ports, numbered one through six. The switch has
been configured to associate VLAN A and B with FID 2, VLAN C and D with FID 3, and VLAN
E with FID 4. Port 6 has been classified as a 1Q Trunk Port. This classification establishes that all
VLANs are members of the Port VLAN List for Port 6 and the frames transmitted for all VLANs
will contain a tag header. Also the PVID for Port 6 is set to the default VLAN with its
corresponding relationship to FID 1. Although untagged frames are not usually present on a 1Q
Trunk Port, any untagged frames received would need to be classified if the port has not been
configured to drop all untagged frames.
Figure 2-1 Inside the Switch
Port 1
Port 4
A
FID 2
D
FID 3
Port 2
Port 5
B
FID 2
E
FID 4
Port 3
C
FID 3
Default
FID 1
Port 6
2599-02
VLAN Operation 2-3
VLAN Switch Operation
2.4.1 Receiving Frames from VLAN Ports
When a switch is placed in 802.1Q Operational Mode, every frame received by the switch must
belong, or be assigned, to a VLAN.
Untagged Frames
The switch receives a frame from Port 1 and examines the frame. The switch notices that this
frame does not currently have a VLAN tag. The switch recognizes that Port 1 is a member of
VLAN A and classifies the frame as such. In this fashion, all untagged frames entering a VLAN
switch assume membership in a VLAN.
NOTE: A VLAN ID is always assigned to a port. By default, it is the Default VLAN
(VLAN ID = 1).
The switch will now make a forwarding decision on the frame, as described in Section 2.4.2.
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.
2.4.2 Forwarding Decisions
The type of frame under consideration and the filter setting of a VLAN switch determines how it
forwards VLAN frames.
2.4.2.1 Broadcasts, 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 VLAN Operation
GARP Switch Operation
2.4.2.2 Known 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.
For example, assume that a frame is received by the switch depicted in Figure 2-1. This frame is a
unicast untagged frame received on Port 3. The frame is then classified for VLAN C. The switch
then makes its forwarding decision by comparing the destination MAC address to its filtering
database. In this case, the MAC address is looked up in the filtering database FID 3, which is
associated with VLAN C and VLAN D. The switch recognizes the destination MAC address of the
frame as being located out Port 4.
Having made the forwarding decision, the switch now examines the Port VLAN List of Port 4 to
determine if it may transmit a frame belonging to VLAN C. If so, the frame is transmitted out Port
4. If Port 4 has not been configured to transmit frames belonging to VLAN C, the frame is
discarded.
2.5 GARP SWITCH OPERATION
Some or all ports on the switch may be activated to operate under the Generic Attribute
Registration Protocol (GARP) applications, GVRP and/or GMRP. For a description of the
protocols and how the frames are handled, refer to the user’s guide of your SmartSwitch device.
VLAN Operation 2-5
3
VLAN Configuration
This chapter describes how to set up the switch for local or remote management, and the VLAN
Local Management screens used to create and configure VLANs in a SmartSwitch.
3.1 MANAGING THE SWITCH
The switch may be managed locally via a terminal connected to the COM port, or remotely
(SNMP or Telnet sessions) from a management station connected to a switch port that is a member
of the same VLAN as the switch’s Host Data Port. (By default, this is the default VLAN.) When
the switch is configured with VLANs, special precautions must be taken to use remote
management.
3.1.1 Switch Without VLANs
When the switch is powered up, the switch uses its default settings to switch frames like an 802.1D
switch. In this default configuration, all ports are a member of the default VLAN (VLAN 1)
including the virtual Host Data Port of the switch, so any port can be used to manage the device as
shown in Figure 3-1.
VLAN Configuration 3-1
Managing the Switch
Figure 3-1 Switch Management with Only Default VLAN
802.1Q Switch
1
2
Host
Data
Port
4
5
3 6
NOTE: All ports, including the virtual Host Data Port, are
members of the default VLAN. Therefore, any station
shown may be used as the management station.
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3.1.2 Switch with VLANs
If the switch is to be configured for multiple VLANs, it may be desirable to configure a
management-only VLAN. This allows a management station connected to the management VLAN
to manage all ports on the switch and make management secure by preventing management via
ports assigned to other VLANs.
NOTE: The switch’s virtual Host Data Port, like any other port, has configurable VLAN
membership. For manageability of the device to be maintained, this port must be a
member of the same VLAN as the port to which the management station is connected.
Figure 3-2 shows an example of a switch configured with port 1 on the Management VLAN port
and the other users belonging to VLANs A, B, and C.
3-2 VLAN Configuration
Figure 3-2 Switch Management with VLANs
Managing the Switch
Management
VLAN
VLAN A
VLAN A
802.1Q Switch
1
2
Host
Data
Port
4
5
3 6
VLAN B
VLAN B
VLAN C
7
Set as an 802.1Q Trunk port.
To set up the switch shown in Figure 3-2 to establish a management VLAN on port 1, use the
process described below:
1. Use the Device VLAN Configuration screen for the following:
a. Define a new VLAN named “Management VLAN” (or other suitable name) and its
VLAN ID. In this example, the VLAN ID is set to 2.
b. Set the FID so the Management VLAN has its own number to make the VLAN secure. In
this example, the FID is 3 and no other VLAN should be assigned to this FID. This keeps the
new VLAN from sharing its filtering database with other VLANs in the switch. For details
on defining a VLAN, refer to Section 3.4.1.
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2. Use the Port Assignment Configuration screen for the following:
a. Assign the VLAN ID, 2, of the new Management VLAN to a port. In this example, it is port
1. Leave the Port Mode setting in the default value of HYBRID.
NOTE: It is not necessary to configure a physical port for management on each switch.
Only those switches that will have a management station attached to it need a physical
port assigned to the Management VLAN.
b. Assign the VLAN ID, 2, of the new Management VLAN to the Host Data Port. The port
number will depend on the device. This port is not a physical port and will usually be one
number above the maximum number physical ports on the device, including the ports on any
optional interfaces installed. In this example, it will be port 8. Leave the Port Mode setting
in the default value of HYBRID. For details on assigning a VLAN ID, refer to Section 3.4.2.
VLAN Configuration 3-3
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