Cabletron Systems 802.1Q User Manual
802.1Q VLAN
User’s Guide
9032599-02
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 FOR ANY 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
of Cabletron Systems, Inc.
All other product names mentioned in this manual may be trademarks or registered trademarks of
their respective companies.
and
S
ECUREFAST
are registered trademarks and
S
MARTSWITCH
is a trademark
802.1Q VLAN User’s Guide i
Notice
ii 802.1Q VLAN User’s Guide
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
802.1Q VLAN User’s Guide iii
Contents
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
iv 802.1Q VLAN User’s Guide
Contents
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
802.1Q VLAN User’s Guide v
Contents
vi 802.1Q VLAN User’s Guide
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
802.1Q VLAN User’s Guide vii
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
802.1Q VLAN User’s Guide viii
PREFACE
Welcome to the Cabletron Systems 802.1Q VLAN User’s Guide
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.
. This
USING THIS 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 the VLAN Local Management screens and pro vides 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,
VLANs, including their benefits and uses. This chapter also provides
information about how to obtain additional help if needed.
Virtual Local Area Networks
, presents the basic concepts of
Chapter 2,
VLAN, the steps necessary to prepare an 802.1Q VLAN a ware switch for
VLAN operation, and examines the operation of an 802.1Q VLAN
switch.
Chapter 3,
local and remote management, shows the Local Management screens
used in 802.1Q VLAN configuration and explains their use.
Chapter 4,
how network transmissions are treated by the components of each VLAN.
802.1Q VLAN User’s Guide ix
VLAN Operation
VLAN Configuration
Examples
, offers examples of 802.1Q VLANs and explains
, describes the operation of an 802.1Q
, describes how to set up the switch for
Preface
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:
Note
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
x 802.1Q VLAN User’s Guide
denotes complete book titles.
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 DEFINING VLANs
A Virtual Local Area Network is a group of devices that function as a
single Local Area Netw ork se gment (broadcast domain). The de vices 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. Tw o b uildings
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 1-1
Chapter 1:
Virtual Local Area Networks
Building One Building Two
SS
S
FF
A
SmartSwitch SmartSwitch
S
Member of Sales Network
10
9
1
Figure 1-1 Example of a VLAN
trunk
8
F
Member of Finance Network
SSS
FF
7
6
B
2263-01
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.
1-2 802.1Q VLAN User’s Guide
Types of VLANs
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.
1.2.1 802.1Q 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
Cabletron Systems’ SecureF ast 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.
802.1Q VLAN User’s Guide 1-3
Chapter 1:
Virtual Local Area Networks
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 VLAN T ERMS
T o 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.
1-4 802.1Q VLAN User’s Guide
VLAN Terms
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.
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 T runk
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.
802.1Q VLAN User’s Guide 1-5
Chapter 1:
1D T runk
Virtual Local Area Networks
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.
1-6 802.1Q VLAN User’s Guide
Getting Help
1.5 GETTING HELP
For additional support related to this device or document, contact
Cabletron Systems using one of the following methods:
World Wide Web http://www.cab letron.com/
Phone (603) 332-9400
Internet mail support@cabletron.com
FTP ftp://ftp.cabletron.com/
Login
Password
To send comments or suggestions concerning this document, contact the
Cabletron Systems Technical Writing Department via the following
email address:
Make sure to include the document Part Number in the email message.
TechWriting@cabletron.com
Before calling Cabletron Systems, have the following information
ready:
•
Your Cabletron Systems service contract number
•
A description of the failure
anonymous
your email address
•
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
802.1Q VLAN User’s Guide 1-7
Chapter 1:
Virtual Local Area Networks
1-8 802.1Q VLAN User’s Guide
CHAPTER 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.
802.1Q VLAN User’s Guide 2-1
Chapter 2:
VLAN Operation
2.3 CONFIGURATION PROCESS
Before a VLAN can operate, steps must be performed to configure the
switch to establish and configure a VLAN. Cabletron Systems 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,
Configuration
must be taken in very general terms, and is intended only to aid
in the Administrator’s understanding of VLAN switch operation.
.This brief section describes the actions that
VLAN
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.
2-2 802.1Q VLAN User’s Guide
VLAN Switch Operation
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.
2.4 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.
802.1Q VLAN User’s Guide 2-3
Chapter 2:
VLAN Operation
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 w ould need to be classified if the port
has not been configured to drop all untagged frames.
Port 1
Port 2
A
FID 2
D
FID 3
Port 4
Figure 2-1 Inside the Switch
Port 5
B
FID 2
E
FID 4
Port 3
C
FID 3
Default
FID 1
Port 6
2599-02
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
2-4 802.1Q VLAN User’s Guide
A VLAN ID is always assigned to a port. By default, it is the
Default VLAN (VLAN ID = 1).
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.
2.4.2 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.
2.4.2.2 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.
802.1Q VLAN User’s Guide 2-5
Chapter 2: VLAN Operation
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.
2-6 802.1Q VLAN User’s Guide
CHAPTER 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 def ault, 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.
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.
2599_14
Figure 3-1 Switch Management with Only Default VLAN
802.1Q VLAN User’s Guide 3-1
Chapter 3: VLAN Configuration
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.
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.
Figure 3-2 Switch Management with VLANs
25992_15
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.
3-2 802.1Q VLAN User’s Guide
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