Cabletron Systems 802.1Q VLAN User manual

9032599-02
802.1QVLAN
User’s Guide

802.1QVLAN User’s Guide i
NOTICE
Cabletron Systems reserves the right to make changes in specifications and other information
contained in this document without prior notice. The reader should in all cases consult Cabletron
Systems to determine whether any such changes have been made.
The hardware, firmware, or software described in this manual is subject to change without notice.
IN NO EVENT SHALL CABLETRON SYSTEMS BE LIABLE FORANY INCIDENTAL,
INDIRECT, SPECIAL, OR CONSEQUENTIAL DAMAGES WHATSOEVER (INCLUDING BUT
NOT LIMITED TO LOST PROFITS) ARISING OUT OF OR RELATED TO THIS MANUAL OR
THE INFORMATION CONTAINED IN IT, EVEN IF CABLETRON SYSTEMS HAS BEEN
ADVISED OF, KNOWN, OR SHOULD HAVE KNOWN, THE POSSIBILITY OF SUCH
DAMAGES.
 1999 by Cabletron Systems, Inc., P.O. Box 5005, Rochester, NH 03866-5005
All Rights Reserved
Printed in the United States of America
Order Number: 9032599-02 February 1999
Cabletron Systems and S
ECURE
F
AST
are registered trademarks and S
MART
S
WITCH
is a trademark
of Cabletron Systems, Inc.
All other product names mentioned in this manual may be trademarks or registered trademarks of
their respective companies.

Notice
ii 802.1QVLAN User’s Guide

802.1QVLAN User’s Guide iii
CONTENTS
Figures ....................................................................................................vii
Tables.....................................................................................................viii
PREFACE
Using This Guide............................................................................ix
Structure of This Guide...................................................................ix
Related Documents.........................................................................x
Document Conventions...................................................................x
CHAPTER 1 VIRTUAL LOCAL AREA NETWORKS
1.1 Defining VLANs...........................................................................1-1
1.2 Types of VLANs...........................................................................1-3
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.............................................................1-4
1.4 VLAN Terms................................................................................1-4
1.5 Getting Help.................................................................................1-7
CHAPTER 2 VLAN OPERATION
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..........................2-3
2.4 VLAN Switch Operation...............................................................2-3
2.4.1 Receiving Frames from VLAN Ports...............................2-4
2.4.2 Forwarding Decisions .....................................................2-5
2.4.2.1 Broadcasts, Multicasts, and Unknown
Unicasts..........................................................2-5
2.4.2.2 Known Unicasts..............................................2-5
2.5 GARP Switch Operation..............................................................2-6

Contents
iv 802.1QVLAN User’s Guide
CHAPTER 3 VLAN CONFIGURATION
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
3.2.1 Preparing for VLAN Configuration...................................3-4
3.3 802.1Q VLAN Configuration Menu Screen..................................3-5
3.4 Device VLAN Configuration Screen.............................................3-8
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....................................3-21
3.7.1 Viewing Current VLAN Ports.........................................3-22
3.7.2 Paging Through VLAN Forwarding List Entries.............3-23
3.7.3 Adding Forwarding List Entries .....................................3-23
3.7.4 Deleting Forwarding List Entries ...................................3-23
3.7.5 Changing the Frame Format.........................................3-24
3.8 Protocol VLAN Configuration Screen.........................................3-24
3.8.1 Displaying the Current Protocol, VLAN ID, and
Port Assignments..........................................................3-28
3.8.2 Assigning a Protocol Family to a VLAN ID....................3-28
3.8.3 Displaying the Protocol Types on Current Ports ...........3-30
3.9 Protocol Ports Configuration Screen..........................................3-31
3.9.1 Adding/Deleting Ports Associated with a VLAN ID........3-33
3.10 Quick VLAN Walkthrough ..........................................................3-33

Contents
802.1QVLAN User’s Guide v
CHAPTER 4 EXAMPLES
4.1 Example 1, Single Switch Operation...........................................4-1
4.1.1 Solving the Problem........................................................4-2
4.1.2 Frame Handling ..............................................................4-3
4.2 Example 2, VLANs Across Multiple Switches..............................4-4
4.2.1 Solving the Problem........................................................4-5
4.2.2 Frame Handling ..............................................................4-8
4.3 Example 3, 1D Trunk Connection to 802.1Q VLAN Network....4-10
4.3.1 Solving the Problem......................................................4-12
4.3.2 Frame Handling ............................................................4-13
4.4 Example 4, Isolating Network Traffic According to Protocol......4-17
4.4.1 Solving the Problem......................................................4-18

Contents
vi 802.1QVLAN User’s Guide

802.1QVLAN User’s Guide vii
FIGURES
Figure Page
1-1 Example of a VLAN..................................................................1-2
2-1 Inside the Switch......................................................................2-4
3-1 Switch Management with Only Default VLAN..........................3-1
3-2 Switch Management with VLANs.............................................3-2
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.....................................3-25
3-10 Protocol Ports Configuration Screen......................................3-31
3-11 Walkthrough Stage One.........................................................3-35
3-12 Walkthrough Stage Two.........................................................3-36
3-13 Walkthrough Stage Three ......................................................3-37
3-14 Walkthrough Stage Four ........................................................3-38
3-15 Final Walkthrough Stage........................................................3-40
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 ..........................4-5
4-4 Bridge 1 Broadcasts Frames....................................................4-8
4-5 Transmitting to Switch 4...........................................................4-9
4-6 Transmitting to Bridge 4.........................................................4-10
4-7 Example 3, 1D Trunk Connection to 802.1Q VLAN Network.4-11
4-8 Bridge 1 Broadcasts Frames..................................................4-14
4-9 Switch 2 Forwards to 1Q Trunk..............................................4-15
4-10 Switch 1 Forwards to 1D Trunk..............................................4-15
4-11 Example 4, Isolating Traffic According to Protocol.................4-18

802.1QVLAN User’s Guide viii
TABLES
Table Page
3-1 802.1Q VLAN Configuration Menu Screen Menu Items ..........3-7
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 .............3-19
3-5 VLAN Forwarding Configuration Screen Field Definitions .....3-22
3-6 Protocol VLAN Configuration Screen Field Definitions .........3-26
3-7 Protocol Ports Configuration Screen Field Definitions ..........3-32

802.1QVLAN User’s Guide ix
PREFACE
Welcome to the Cabletron Systems 802.1Q VLAN User’s Guide . This
guide introduces and describes Cabletron Systems’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
Cabletron Systems products used in 802.1Q VLAN environments.
USINGTHIS GUIDE
This guide serves as a supplement to the Local Management chapter of
the Cabletron Systems 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 theVLAN Local Management screens and provides a
quick walkthrough on how to use them to configure VLANs in a switch.
STRUCTURE OFTHIS 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 802.1QVLAN aware switch for
VLAN operation, and examines the operation of an 802.1Q VLAN
switch.
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.

Preface
x 802.1QVLAN User’s Guide
RELATED DOCUMENTS
Other Cabletron Systems 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 Cabletron Systems 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.cabletron.com/
DOCUMENT CONVENTIONS
The following conventions are used throughout this document:
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.
NOTE
Note symbol. Calls the reader’s attention to any item of
information that may be of special importance.

802.1QVLAN User’s Guide 1-1
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.
1.1 DEFININGVLANs
A Virtual Local Area Network is a group of devices that function as a
single LocalArea Network segment (broadcast domain). The devices that
make up a particularVLAN 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 basedVLAN. 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.

Chapter 1: Virtual Local Area Networks
1-2 802.1QVLAN User’s Guide
Figure 1-1 Example of aVLAN
In this example, the Sales and Finance workstations have been placed on
two separateVLANs. 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 SmartSwitchA, be sent to the
ports connected to other local members of the SalesVLAN, 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
SS
FF
A6
SSS
FF
B
7
8
9
10
Building One Building Two
SmartSwitch SmartSwitch
trunk
2263-01
S
Member of Sales Network Member of Finance Network
SF

Types ofVLANs
802.1QVLAN User’s Guide 1-3
1.2 TYPES OFVLANs
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.
1.2.1 802.1QVLANs
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
Cabletron Systems’SecureFastVLAN 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 OtherVLAN 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.

Chapter 1: Virtual Local Area Networks
1-4 802.1QVLAN User’s Guide
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.
1.4 VLANTERMS
To fully understand the operation and configuration of port basedVLANs,
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.

VLANTerms
802.1QVLAN User’s Guide 1-5
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 (VLANTag)
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.
DefaultVLAN
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.
PortVLAN 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.
1QTrunk
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 allVLANs in its PortVLAN 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.

Chapter 1: Virtual Local Area Networks
1-6 802.1QVLAN User’s Guide
1DTrunk
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.
GARPVLAN 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.

Getting Help
802.1QVLAN User’s Guide 1-7
1.5 GETTING HELP
For additional support related to this device or document, contact
Cabletron Systems using one of the following methods:
Before calling Cabletron Systems, have the following information
ready:
• Your Cabletron Systems 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 Cabletron Systems
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
World Wide Web http://www.cabletron.com/
Phone [phone]
Internet mail suppor[email protected]
FTP ftp://ftp.cabletron.com/
Login anonymous
Password your email address
To send comments or suggestions concerning this document, contact the
Cabletron SystemsTechnical Writing Department via the following
email address: [email protected]
Make sure to include the document Part Number in the email message.

Chapter 1: Virtual Local Area Networks
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