Madge LANswitch 3LS Application Guide

Madge Networks, January 1997
LANswitch 3LS
Application Guide
Building a Better Network with Multilayer IP/IPX Switching

LANswitch 3LS Application Guide
Page 1
Table of Contents
Introduction............................................................................................................3
What network problems does the LANswitch 3LS solve?......................................4
LANswitch 3LS features and advantages..............................................................7
Which networks can benefit from the 3LS ...........................................................11
LANswitch 3LS Applications ................................................................................19
Appendix: IP/IPX plus other network protocols....................................................29

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Introduction
MadgeOne™
calls for the integration of data, voice and video applications over a single network
infrastructure. While the vision of MadgeOne multiservice networks is indeed revolutionary, the
implementation of MadgeOne can only be evolutionary, because in real life, networks don’t change
overnight. Upgrading the enterprise network without causing a major upheaval is the challenge faced by IS
managers today. The LANswitch™
3LS Multilayer IP/IPX switch is one of the many ways in which Madge
Networks is meeting this challenge.
How will multiservice networks become a reality? - one step at a time. There are no shortcuts to a fully
integrated networking system. Over time, a series of logical migration steps must ensure that every new
component fits it and contributes incremental benefits to the overall solution, without limiting the options
for future growth. That’s why Madge does not believe in “fast-packet” point products that can only be
accommodated by changing the existing network. In most cases you will find that point solutions are just
another foreign box, added to the network without considering the impact it will have on future network
expansion, migration or manageability.
In contrast, the LANswitch 3LS is standards-based and designed as an integral part of the Madge
LANswitch system. The 3LS transforms the LANswitch hub into a powerful multilayer/multiprotocol
switch that boosts the performance of existing networks by seamlessly forwarding data within and between
logically defined network groups. The 3LS opens up LANswitch to a new class of advanced applications,
and is a logical stepping-stone in the gradual evolution to multiservice networks.
The LANswitch 3LS combination of price, performance, functionality, and investment protection makes it
a superior alternative to expensive, router-based solutions. The LANswitch 3LS uses advanced silicon
technology which is fast, yet inexpensive. In this way the LANswitch 3LS delivers wire-speed performance
and multilayer switching functionality for a fraction of the price of a router . Because the LANswitch 3LS
is completely interoperable with all standards-based routers, it provides a solution that complements and
enhances current networks, without requiring wholesale changes to the network infrastructure. Moreover,
the LANswitch 3LS is modular, scalable solution that lets you continue to expand, upgrade, and migrate
the network gradually and cost-effectively. There is no better investment protection than a free scaling
system.
Most enterprise networks are used for data transfer. Integrated voice and video is viewed as the next major
step to be taken by corporate networks, but in the meantime, the business-critical applications that run on
these data networks need an immediate solution for their current bandwidth and performance problems.
The LANswitch 3LS is available today and it addresses this need for heavy-duty data backbones that
provide switching performance for all types of network traffic. At the same time, the LANswitch 3LS is
designed to support voice and video applications as they emerge, so it’s ready for your organization’s
future plans. The LANswitch 3LS performs with low and constant delays; uses priority mechanisms to
guarantee Quality of Service, and is slated to support Layer 3 QoS in the future.

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What Network Problems does the LANswitch 3LS Solve?
LAN switches are simple, cost-effective and offer excellent performance. When we need to increase the
capacity of the LAN, ideally, we should migrate the entire LAN infrastructure to operate exclusively on
LAN switches. However, in many cases there is some necessity for routing in the LAN due to IP
subnetting, the need for broadcast control, security concerns or because the LAN contains a mix of
technologies.
The fact of the matter is that routers are much more complex and more costly than LAN switches. In
addition, a good deal of software is involved in processing each packet through a router, so it is generally
much slower than a LAN switch, and harder to configure and manage.
The LANswitch 3LS answers the need for fast routing in the LAN and provides a solution to the problems
that make router-based networks cumbersome:
Deteriorating Network Performance
• Increasing number of users
Adding users to the network means increasing the number of users that must share the available
bandwidth as well as increasing the internetworking load that the routers must handle. Unless
measures are taken to increase the amount of available bandwidth, network performance typically
deteriorates in direct correlation to the number of users on the LAN.
• Increasing number of segments
As more and more users are added to the network, the network administrator is usually compelled to
increase the number of LAN segments in the network. Even if existing routers have enough ports to
accommodate these new segments, the increased traffic that must travel through the router will
exhaust the router’s memory and CPU resources, causing network performance to plummet.
Eventually, more segments will require the purchase of more routers.
• Increasingly demanding applications
Voice and video transmission require low and constant latency (delay). Routers cannot support many
delay-sensitive applications such as video-conferencing, because their software-based CPU introduces
relatively high and variable delays into the transmission. Likewise, it is doubtful that routers will be
able to operate at the speeds required by newer high-bandwidth technologies such as 622 Mbps OC-12
or Gigabit Ethernet.
Network Management that is out of control
• Increasing number of users
Small networks - small problems; Big networks - big problems. As the number of users increases, the
network inherently becomes harder to manage. Routers and users must be aware of each other’s
existence, which necessitates extra configuration and management tasks.

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• More protocols, more complexity
Although routers perform different roles in different environments, it is common practice to use the
router for a broad range of functions, including both LAN and WAN communications as well as
protocol conversion. These are complicated tasks that demand detailed configuration of the router.
Complex configuration and constant administration is probably the biggest headache associated with
routers. Network administrators must determine and configure a large number of network parameters
for each router in the network, and many times, these parameter sets are different for each protocol
stack that the router supports. Moreover, to make sure that all routers in the network can talk to one
another, the parameters of one router must be consistent with those of all the other routers. Router
administration is a complex, time-consuming, and ongoing process - especially for larger networks.
• Physical constraints
In a router based network, network design, configuration, and subnetting is restricted by the physical
router interfaces and the number of ports and protocols that each router supports. In other words, your
network expansion plans must be tailored to “fit” the router, rather than tailored to properly address
the network requirements at hand.
• Hard to track moves and changes
In a router-based network, IP/IPX segments are determined by their physical connection to the router.
Moving a user from one IP subnet to another (i.e., from one router port to another) necessitates a
whole slew of reconfigurations.
Spiraling cost of ownership
• Expensive purchase price
Routers are much more complex than LAN switches, and therefore, more costly. Faster router ports
(i.e., 100 Mbps) cost even more. When segmentation is restricted to the number of physical router
ports available, network expansion becomes a very expensive proposition indeed.
• High maintenance costs
Routers require ongoing administration, which means that you must have adequately trained staff on
hand at all times.
• High upgrade costs
The cost of upgrading a router does not stop at the price of the additional router ports. Typically,
additional router ports must be accompanied by software and CPU upgrades to support the router’s
expanded capacity.
• Expensive to scale upward
In many cases, replacement is the only way to upgrade an existing router. Due to architectural
limitations, most router models can be upgraded only so far, and the gain in performance may not be
sufficient to answer your internetworking requirements. Hence, an expensive forklift upgrade to one of

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the router vendor’s “new and improved” line of routers may be the only way he can deliver the level of
performance you are trying to obtain.
LANswitch 3LS is the solution
The LANswitch 3LS is an integral part of a comprehensive Madge switching solution that addresses and
solves the problems of deteriorating performance, complex network management and the spiraling cost of
router-based networks.

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LANswitch 3LS Features and Advantages
The strength of 3LS is the part it plays in providing a comprehensive LANswitch backbone solution. The
3LS makes LANswitch the most feature-rich, integrated multilayer switching solution in the industry. The
LANswitch 3LS complements existing routers rather than replaces them. Its multilayer functionality is in
fact, much more scalable and cost-effective than conventional solutions consisting of Layer 2 switch +
router configurations. What benefits does the LANswitch 3LS bring to today’s networks?
• Integrated multilayer IP/IPX switching
• Exceptional price, performance, and functionality
• Interoperability that complements existing networks
• True Virtual LAN intelligence
• Investment protection
Integrated Multilayer IP/IPX Switching
With the introduction of the LANswitch 3LS, Madge has built network layer switching onto the solid
foundation of Layer 2 switching that LANswitch has had all along. LANswitch offers a full range of
Ethernet and Fast Ethernet port and segment switching capabilities, plus switched backbone options that
include full-duplex Fast Ethernet, FDDI and ATM. And a brand new suite of switch management
applications rounds out the LANswitch offering, making it one of the most comprehensive switching
solutions on the market today. The result puts LANswitch in a league of its own, as the networking
industry’s only true multilayer switch with fully integrated Layer 2 and Layer 3 services.
LANswitch incorporates Layer 2 bridging and Layer 3 routing in the same switching fabric, so it can
support network layer subnets and VLANs without having to pass traffic off to a separate router, or request
routing information from a route server. The LANswitch 3LS specializes in IP and IPX protocols and
executes all Layer 3 processing in fast VLSI hardware. For LANswitch users, this provides a level of
integration and flexibility that makes physical and logical networks transparent.
Furthermore, since the LANswitch 3LS is a fully integrated part of the LANswitch hub, it is fully
monitored by Madge SMON. SMON gives network managers an unobstructed view of all LANswitch
activity at both the MAC and Network layer. Non-integrated solutions can’t even come close to providing
this level of network visibility. In addition, Madge’s Advanced VirtualMaster (AVM) management
application makes it easy to implement Virtual LANs on a large scale by automating VLAN assignment
and maintenance.
Exceptional Price/Performance/Functionality
When compared to routers, a solution based on LANswitch 3LS is both faster and less expensive. A typical
router supports a full complement of network protocols, however IP and IPX represent the majority of
Layer 3 requirements in the LAN. By focusing its operation on IP and IPX, the LANswitch 3LS is able to
successfully optimize IP/IPX switching and deliver wire-speed performance. While the LANswitch 3LS
does not aim to eliminate conventional routers, it greatly reduces their role in the switched network, so that

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a router may only be needed as a gateway to the WAN or to perform complex routing functions such as
protocol conversions.
Perhaps the bottom line tells all. A 1 Gbps router can easily run into the hundred-thousand dollar price
range. In contrast, the LANswitch 3LS, which switches across a multi-Gigabit backplane, can be had for
much, much less. Simply put, LANswitch 3LS delivers better performance at a fraction of the cost of a
traditional router.
Interoperability that complements existing networks
The LANswitch 3LS fully supports standard router-to-router protocols, including RIP and OSPF, which
enable it to interoperate with existing routers. The LANswitch 3LS “looks” like a router to all stations and
to all other routers in the network, so there is no need to modify existing desktops or applications in order
to communicate with the LANswitch 3LS.
The simplicity and interoperability of the LANswitch 3LS give corporate networks the freedom to
implement upgrades according to their specific needs and at their own pace. The LANswitch 3LS can just
as easily be deployed in a limited (focused) way to enhance performance in select parts of the network – or
applied throughout the enterprise, to improve overall performance and advance the network according to a
coherent migration strategy.
True Virtual LAN Intelligence
Virtual LANs partition the switched network into separate domains such that all users inside a domain can
communicate directly with each other, but communication across domain boundaries requires an
internetworking device. In more technical terms, this means the ability to partition a switched network into
distinct broadcast and unicast domains. VLANs also give you the flexibility to define networked
workgroups whose members who are physically dispersed throughout the network.
The LANswitch 3LS makes VLANs highly usable because an integral part of its operation includes full
awareness of VLAN memberships (unlike a router which has no knowledge of VLANs). Consider a
campus environment with 30-50 virtual LANs distributed across several floors or buildings. Stations
within the same VLAN communicate via direct Layer 2 switching. However, communications across
VLAN boundaries must go through an internetworking device. A conventional router would have to have
30-50 ports and enough bandwidth to prevent it from becoming a bottleneck. This is a very expensive
proposition.
On the other hand, with a LANswitch 3LS multilayer switch, packets never leave the switching fabric. No
matter how many VLANs you create, there is no need to buy additional physical internetworking ports.
The modular 3LS sits on the LANswitch backplane, so it automatically has a “leg” in every Virtual LAN.
Since the 3LS is inherently VLAN-aware, it can speedily switch packets from one VLAN to another.
In addition, Madge’s Advanced VirtualMaster (AVM) management application makes it easy to
implement Virtual LANs on a large scale by automating VLAN assignment and maintenance.

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Router
Subnet
1
Subnet
3
Subnet
2
LANswitch
3LS
VLAN 2
VLAN 3
VLAN 1
Figure 1: A conventional router typically
dedicates one port to each logical network it
connects. Adding logical networks (or VLANS)
means adding router ports at a hefty price per
port.
Figure 2: The 3LS has a leg (connection) in
each VLAN courtesy of the LANswitch
backplane. No additional ports are needed no
matter how many VLANs are configured.1
LANswitch
Traffic within a VLAN
is switched at Layer 2
LANswitch
3LS
VLAN 1 VLAN 2 VLAN 3 VLAN 4 VLAN 4
Traffic between VLANS
is switched at Layer 3
by the 3LS
Figure 3: It is not necessary to install a 3LS in each LANswitch hub,. VLAN traffic can traverse
high-speed LANswitch backbone modules, enabling the 3LS to service VLANs across mulitple
LANswitch hubs.
1
With the 3LS, IP and IPX subnets are no longer associated with a particular router port. This allows
IP/IPX subnets to be distributed over many hubs and many locations.

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Investment Protection
The LANswitch multilayer switch is installed first and foremost for performance, but the following
features make sure you get the most from your network investment:
• Standards-based design and operation
• Future ready - easy implementation of Layer 2 switching; easy addition of Layer 3 switching; QoS and
more.
• Open architecture
The LANswitch 3LS is an open, standards-based product that allows enhanced capabilities to be added as
an integral part of the switching architecture. Many of today’s technology hurdles will be overcome as
standards are developed and implemented throughout the industry (e.g., QoS over IP networks using
RSVP). Madge products are deliberately designed to be able to adopt and comply with industry standards
as they emerge. This ensures that our customer will continue to have open options as they migrate their
network infrastructure.
The No-Compromise Systems Solution
Multilayer switches must be part of a complete switching system. A company that constructs an enterprise
network based on Layer 2 switches, interconnected via high-speed backbone links, must be able to add
Layer 3 switching functionality without compromising the performance or capability of the Layer 2
infrastructure already in place. If the network supports multiple protocols (i.e., Ethernet, Fast Ethernet,
FDDI, etc.), the multilayer switch should provide equivalent support. A management console that monitors
switched traffic at Layer 2 should also be able to view the packets that are switched at Layer 3. VLANs
created by Layer 2 switches should be fully supported by the multilayer switch, without changing virtual
network definitions. The multilayer switch must also be as resilient, scalable, and manageable as the rest of
the network.
Standalone boxes, even though they may have wonderful features, remain separate from the integrated
switching system, hidden from management’s view, in danger of becoming a single point of failure, and
not scalable with the rest of the network. Furthermore, most of them rely on non-standard, proprietary
protocols.
The LANswitch 3LS is part of a complete switching system. The 3LS module is thoroughly integrated with
all LANswitch hubs, adding Layer 3 functionality on top of a solid and proven foundation of Layer 2
switching capability. When located in the central backbone of a building, it can switch and route traffic
coming from Visage switches or other LANswitches. The LANswitch 3LS also switches/routes network
traffic over ATM, FDDI or Fast Ethernet campus backbones. All the resilience and scalability of the
modular LANswitch architecture is automatically conferred upon the 3LS, as well as full visibility and
manageability via Madge SMON switch monitoring and Advanced VirtualMaster applications.

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Which Networks can Benefit from the 3LS
The LANswitch 3LS supplies multilayer switching solutions to networks based on IP, IPX or a mix of IP
and IPX. The first step in upgrading any network is to identify the logical network structure, because that
will determine how to best deploy the LANswitch 3LS. In this guide, we will examine four types of
networks:
1. Pure IP networks.
2. Pure IPX networks (although pure IPX networks are less common, we will use this to highlight the
different requirements of each protocol).
3. A mix of IP and IPX in the network.
4. Networks based on IP/IPX, but combined with other routable or non-routable protocols, such as
DECnet, Appletalk, DEC LAT, and NetBIOS.
The following sections describe how the LANswitch 3LS would be deployed in each of these situations.
We will use the collapsed backbone router configuration as our starting point, apply the 3LS solution, and
explain the implementation in each network environment. The only vendor-specific hardware in these
applications is the LANswitch Multilayer Switch. Other equipment could be from any vendor.
1. Pure IP Networks
The starting point:
The diagram below shows a router deployed as a central collapsed backbone in the LAN. Several shared
Ethernet segments are connected to the router. Each connection represents a separate IP subnet.
Centralized servers are directly connected to the router (also on their own subnet). The router that provides
communication between subnets is slow, has limited (and expensive) expansion options, and requires a
great deal of administration to deal with moves and changes in the network.
IP
Subnet 1
IP
Subnet 2
IP
Subnet 3
IP Subnet 5
IP Subnet 4
Router
IP Subnet 6
Figure 4: Router as collapsed backbone in an IP network

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Multilayer Switching Introduced
The goal of the LANswitch 3LS and its Layer 3 switching services is to shift internetwork traffic from the
router to the switch, where packets will be transferred at a much faster rate. With the LANswitch 3LS, IP
network managers can integrate Layer 3 switching with minimal disruption and reconfiguration of the
existing network. Figure 5 illustrates how this can be done.
Ethernet segments have been disconnected from the router and connected to an LSE-404S segment
switching module in the LANswitch hub. The 3LS module is also installed in the hub. This creates a
switched internetworking structure, where packets are forwarded between segments via the Cellenium™
switching fabric. Theoretically, the router becomes extraneous - however, in many cases, the router will
stay on to fulfill the role of handling other routable protocols that may be present in the network, such as
DECnet or Appletalk.
IP Subnet 4
IP Subnet 5
IP Subnet 6
IP
Subnet 2
IP
Subnet 3
LANswitch
IP
Subnet 1 3LS
Figure 5: LANswitch 3LS off-loads the router
Back in Figure 4, each subnet was connected to a single router port.2
Every end-station in an IP network is
configured to know to which IP subnet it belongs, and the specific “default gateway” (i.e., router) to which
it should send packets whose destination is in a different subnet. Likewise, the router knows which subnet
is connected to each of its ports. However, we no longer want IP end-stations to automatically send packets
to that router. We want all IP stations to forward data to the 3LS. How is this accomplished without
reconfiguring the end-stations? Very simply.
IP subnets that used to be correlated with the router, will now be correlated with the 3LS. First, a simple
configuration procedure “re-assigns” the router’s interface addresses to the 3LS. Next, the IP address of
each router interface must be modified, either to a different subnet or host number. This prevents the router
from being selected as the default gateway by mistake. The result is that the router is taken out of the IP
internetworking loop. Meanwhile, the end-stations still think and act as if they are sending packets to the
2
Some routers can have more than one logical subnet connected to a single router port. To keep things
simple, let’s assume one router port per subnet.

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router, even though in reality, packets are being forwarded to the 3LS. In this way, the 3LS lets you
integrate Layer 3 switching into the network, without touching the desktop.
Now that the servers are connected directly to the switch, they are no longer subject to the configuration
limitations that were imposed by the router. With LANswitch 3LS, servers can be assigned to the same IP
subnet as their clients and yet be distributed throughout the network. Traffic within each subnet is switched
at Layer 2, while traffic between subnets is switched at Layer 3 by the 3LS.
3LS
IP-2 IP-3IP-1
IP-4
Router IP address 1
Router IP address 2
Router IP address 3
Router IP address 4
IP
Subnet 1
IP
Subnet 2
IP
Subnet 3
IP 2
IP 1
IP 3
(router)
Figure 6: Router IP addresses re-assigned to the 3LS
3
3
The 3LS correlation tables shown throughout this document are for illustration purposes only, and are
not meant to depict the actual user interface.

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2. Pure IPX Networks
The starting point:
Figure 7 shows a logical rendition of an IPX topology. The diagram shows three separate IPX networks,
each one with its own server. The servers are all interconnected via a common IPX network. The servers
are responsible for routing packets between the three IPX networks. In general, servers do not make very
good routers, and in any case, if a server is bogged down with internetworking tasks, it has less resources
to allocate to the clients on its network.
IPX
Net 1
IPX
Net 2
IPX
Net 3
WAN
Figure 7: IPX network with interconnected servers
In IPX, we define separate IPX networks by configuring each IPX server and its clients in a separate
VLAN. If no VLANs are defined, all IPX users are therefore in one IPX network and no routing is
required. However, our discussion presumes IPX segmentation (multiple networks) and hence, routing is a
network requirement. The goal of the 3LS is to shift internetwork traffic from the IPX servers to the
switch. Packets will be transferred at a much faster rate, and the IPX servers will be free to function as
first-rate servers, rather than second-rate routers. With the LANswitch 3LS, IPX network managers can
integrate Layer 3 switching with minimal disruption and reconfiguration of the existing network.
Physically each IPX segment connects to an LSE-404S or LFE-4004+ port, and each server to an LFE-
4004 port in the LANswitch hub.
IPX
Net 1
IPX Net 2
IPX
Net 3
LANswitch
3LS
Figure 8: IPX segments and servers connected to LANswitch

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Now we must implement another step that was optional in the IP network, but which is critical to the IPX
configuration. In IP networks, each station is assigned a unique IP address that is fixed and can only be
changed through reconfiguration. In contrast IPX network addresses are assigned more dynamically.
Whenever an IPX station boots up and logs onto the network, it learns its network number from a server or
servers by means of a broadcast request.
By connecting all IPX segments and servers to the switch, we have created a flat network structure. In
effect, we now have a situation where all the IPX stations and servers belong to the same IPX broadcast
domain. The physical network distinctions are gone. When a station boots up and logs into the network, it
will receive the same network assignment (broadcast domain) as every other station because they are all
connected to the same domain.
For the network manager who wants to get rid of discrete networks and move to a flat network topology,
this configuration works fine. However, for a variety of reasons, including better broadcast control,
security, and access control, some customers are keen on keeping their subnetted infrastructure. Since we
are no longer defining separate IPX networks by their “physical” connections, we must define them
logically, i.e., using Virtual LANs. The IPX protocol demands that each IPX segment reside on a separate
network.
3LS
IPX
Net 1
IPX Net 2
IPX
Net 3
V2
LANswitch
V1
V3
Figure 9: IPX subnets mapped to Virtual LANs
Technically, the network manager maps one Virtual LAN for every IPX network connected to the switch,
such that stations on IPX network #1 belong to VLAN #1, and so on. Mapping each IPX network into a
VLAN re-establishes the segmented network structure that was originally there. Next, all Virtual LAN
definitions must be communicated to the 3LS. so that now, the 3LS correlation table contains the following
information:
• The IPX network address of the segment or server
• The VLAN to which the segment or server is mapped

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3LS
IPX 1,
IPX 2,
IPX 3,
Interface 1,
Interface 2,
Interface 3,
VLAN 1
VLAN 2
VLAN 3
Figure 10: VLAN mapping added to the 3LS correlation table
Now, whenever an IPX station boots up and logs into the network, it will receive its network assignment
from the server in its VLAN domain, and the 3LS will handle the requisite routing between VLANs. Since
255 Virtual LANs can be configured in the LANswitch network, IS managers can take this opportunity to
microsegment the network even further, if so desired. Although the IPX protocol allows only one IPX
network per VLAN (broadcast domain), that same VLAN can contain many IP segments.
3. Networks that are a mixture of IP and IPX
We have described how the 3LS could be integrated into a pure IP or IPX network. In practice however,
most enterprise networks are not based on a single network protocol, but comprise a combination of IP and
IPX LANs (as well as others).
By using a combination of the pure IP and pure IPX solutions mentioned above, we can easily
accommodate both IP and IPX in the switched LAN, divide the switched LAN into multiple, separate
broadcast domains, and forward packets between IP/IPX segments via the 3LS multilayer switch. This
preserves the same scheme of subnetting that was used to connect IP and IPX segments (broadcast
domains) together via a conventional router backbone. However in the multilayer switch, these broadcast
domains are defined via logical VLANs rather than physical router connections.
The Starting Point
IP/IPX
IP/IPX IPX
IPX
IP/IPXIPX
IP Severs
Figure 11: IP and IPX networks interconnected via a conventional router
Figure 11 shows and IP/IPX network whose various subnets are interconnected by a router. The router
provides communication between subnets, however it is slow, has limited (and expensive) expansion
options, and requires a great deal of administration to deal with moves and changes in the network.

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The deployment of the LANswitch 3LS in IP/IPX networks follows a combination of the methods we used
for pure IP and pure IPX networks. The simplest and most straightforward configuration is to create a
completely flat network comprising a single IPX network, as many IP subnets as desired, and no VLANs.
The first step is to connect each IP/IPX segment to an LSE-404S port (a Fast Ethernet LFE-4004+ or
LEB-200 can also be used) in the LANswitch hub. Servers can be given dedicated 10 or 100 Mbps
connection to the LANswitch hub.
IPX1IP6, IPX1 IPX1
IP6
3LS
IP7
IP8
IP7, IPX1
IP8, IPX1
WAN
IP23
IP6LSE-404S
LFE-4004
If you have multiple IPX networks and want to preserve that structure, you must create a separate
broadcast domain for each IPX network. To divide the enterprise network into multiple IPX broadcast
domains, we map one Virtual LAN for every IPX network connected to the switch, such that stations on
logical IPX network #1 belong to VLAN #1, and so on. In other words, all stations belonging to a
particular IPX network or IP segment, should be configured in the same VLAN.
IPX2
IPX3
IP6, IPX1
IPX1
IP6
3LS
IP7
IP8
IP7, IPX2
IP8, IPX3
V1
V2
V3
V3V2
WAN
V4
IP23
Figure 12: Virtual LANs divide the IP/IPX network into discrete LANs

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Next, all interfaces and Virtual LAN definitions are configured in the 3LS correlation table. We simply
define a VLAN around each group of ports that have the same subnet identity, and then connect this
VLAN to a “logical” router port within the 3LS. All of this is easily configured via the network
management console. For simplicity’s sake, our example shows only one IPX network and one IP subnet
per VLAN, but in reality, one IPX network and many IP subnets can belong to the same VLAN. In a
network where each VLAN contains multiple IP subnets, the LANswitch 3LS switches traffic between IP
subnets in the same VLAN as well as the traffic between different VLANs.
3LS
Interface 1,
Interface 2,
Interface 3,
VLAN 1, IP6 / IPX1
VLAN 2, IP7 / IPX8
VLAN 3, IP8 / IPX3
Interface 4, VLAN 4, IP 23
Figure 13: The 3LS correlation table enables speedy Layer 3 switching between all network
segments in the IP/IPX LAN
4. IP/IPX plus other network protocols
The LANswitch 3LS performs Layer 3 switching between IP and IPX. It does not provide routing for other
routable protocols such as DECnet and Appletalk. And some protocols are not routable to begin with
because they do not communicate at the network level. These include NetBIOS, LAT and DLC.
For networks that are primarily based on IP/IPX but also have a smattering of these other protocols, the
LANswitch 3LS offers the following options:
1. Use the 3LS for IP/IPX switching and let a conventional router handle the other protocols.
2. Put each unsupported protocol in its own VLAN. This creates a single broadcast domain for each
protocol, providing Layer 2 switching for all stations within that VLAN.
3. Put unsupported protocols (routable and non-routable) in the same VLAN. Avoid splitting same-
protocol users into multiple VLANs. This will give you greater flexibility in configuring and
managing network traffic and users.
Please see the Appendix of this guide for further discussion of unsupported protocols.

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LANswitch 3LS Applications
Let’s take a look at the logical and physical deployment of the LANswitch 3LS in each of the four network
environments that we have discussed thus far. In each case, this guide will present both a logical and
physical view of the network, showing the original configuration of the network, and how the LANswitch
3LS solution is applied.
As we go through each application, keep this simple VLAN rule-of-thumb in mind:4
Many logical
network segments or subnets may be configured in the same Virtual LAN, but each logical segment or
subnet may belong to only one Virtual LAN.
4
Each IPX network requires its own VLAN.

Page 20
1: Collapsed Routed Backbone in Pure IP Networks
Before LANswitch 3LS After LANswitch 3LS
Subnet 3Subnet 1
Subnet 2
WAN
Subnet 5
Subnet 6
Subnet 4
Subnet 3Subnet 1
Subnet 2
WAN
Subnet 2
Subnet 1
Subnet 3
IP 4
IP 5
IP6
IP 1
IP 3
IP 2
IP
WAN
IP
3LS
LSE-404S
IP 1
IP 2
IP 3
IP 1
IP 3
IP 2
LFE-4004
WAN
• Shared IP segments interconnected by router
backbone.
• Router forwarding rate is far less than wire
speed
• Router creates a bottleneck between clients and
server.
• Router ports are limited and expensive to add.
• Moves and changes require extra
administration.
• Shared IP segments interconnected by multi-
gigabit LANswitch.
• 3LS routes between IP segments at wire speed.
• Servers get switched Fast Ethernet connection.
• IP subnets can be distributed (no longer
dependent upon physical router connection).
• Switch ports are abundant and inexpensive.
• Moves & changes are physically independent.

Page 21
2: Collapsed Routed Backbone in Pure IPX Networks
IPX Net 7
WAN
IPX Net 4
IPX Net 8IPX Net 6
IPX 6
IPX 7
IPX 8
WAN
VLAN 1
VLAN 2
VLAN 3
VLAN 4
IPX
WAN
IPX 4
IPX 6
IPX 8
IP X 7
IPX
WAN
3LS
LSE-404S
V2, IPX7
V3, IPX8
V3, IPX 8
V2, IPX 7
V1, IPX 6
LFE-4004
VLAN 4
• Shared IPX segments interconnected by servers
on a common IPX segment.
• Very limited bandwidth for internetworking.
• Servers bogged down by internetworking tasks
devote less resources to their respective LANs.
administration.
• Shared IPX segments interconnected by multi-
gigabit LANswitch.
• 3LS routes between IPX segments at wire speed.
• VLANs preserve IPX network structure -
without requiring changes to the desktop.

Page 22
3: Collapsed Routed Backbone in Mixed IP/IPX Networks
IP/IPX
IP/IPX
IPX
IP
WAN
IP
IP/IPX
IP2/IPX7
WAN
IP3/IPX7
IP1/IPX6
VLAN 2
VLAN 1
IPX7
IP2
IPX6
IP1
VLAN 3
IP/IPX
IP/IPX
WAN
IP/IPX
IP/IPX
IP & IPX
Servers
VLAN 2
IP2
IP3
IPX7
IP/IPX
VLAN 1
IP1
IPX6
WAN
VLAN 2
3LS
VLAN 2
VLAN 1
VLAN 1
IP2IPX7
IP1IPX6
LFE-4004
LSE-404S
VLAN 3
• IP/IPX segments interconnected by a one-armed
router.
• Router forwarding rate: far less than wire speed
• Router is becoming a bottleneck.
administration.
• Internetworking performance is limited by the
bandwidth of the router link.
• IP/IPX segments interconnected by multi-gigabit
LANswitch.
• 3LS routes between segments at wire speed.
• VLANs preserve IP and IPX network structure -
without requiring changes to the desktop.
• Router remains for WAN access.

Page 23
4: Distributed Routed Backbone in Pure IP Networks - Before 3LS
Logical View
Concentrator
FDDI Campus BB
WAN
Multiple IPs
Multiple IPsMultiple IPs
Physical View
FDDI Campus Backbone
Headquarters Building 2 Building 3
WAN
FDDI
Servers
Concentrator
• Routers provide internetworking within each
building as well as connectivity to the FDDI
campus backbone.
• Further segmentation of the network is limited
by the number and speed of router ports.
• Customer wants to deploy switching to improve
performance, without disrupting or changing the
IP subnetting of the network.

Page 24
4a: Distributed Routed Backbone in Pure IP Networks - After 3LS
Logical View:
FDDI Campus BB
WANConcentrator
Physical View
3LS
LSE-404S
LSF-100
3LS
LSE-404S
LSE-404S
3LS
LSE-404S
FDDI
Servers
Concentrator
Fast
Ethernet
LFE-4004
LSE-404S
WAN
• The LANswitch 3LS can either replace the
router in the building or off-load the router by
acting as a front-end.
• Each 3LS switches traffic between the
building’s IP subnets at wire speed.
• No need to touch the desktop. All configuration
done at 3LS and router levels.
• Expand the number of IP segments on the
switch without sacrificing performance.
• Enables distribution of IP subnets (one IP subnet
can span multiple hubs, buildings, etc.).

Page 25
4b: Distributed Routed Backbone in Pure IP Networks - After 3LS
This alternate configuration shows how switching can be implemented in the FDDI backbone for increased
backbone bandwidth and better performance.
Physical View
3LS
LSE-404S
LSF-100
3LS
LSE-404S
LSE-404S
3LS
LSE-404S
FDDI
Servers
Concentrator
Fast
Ethernet
LFE-4004
LSE-404S
WAN
LSF-100
router in the building or off-load the router by
acting as a front-end.
• Each 3LS switches traffic between the
building’s IP subnets at wire speed.
• LSF-100 enables switched FDDI in the campus
backbone for a significant boost in bandwidth.
• Expand the number of IP segments on the
switch without sacrificing performance.
• Enables distribution of IP subnets (one IP subnet
can span multiple hubs, buildings, etc.)

Page 26
5: Distributed Routed Backbone in Mixed IP/IPX Networks - Before 3LS
Logical View
IP/IPX
FDDI
IP/IPX
WAN
IP/IPX
IP
Physical View
IP/IPX
IP/IPX
IP/IPX
IP & IPX
Servers
IP/IPX
IP/IPX
IP/IPX
IP & IPX
Servers
Headquarters Building 2
WAN
• Routers distributed throughout the building and
across the campus.
• Expansion costs money and performance.
• Customer wants to deploy switching to improve
performance, without disrupting or changing the
IP/IPX subnetting of the network.

Page 27
5a: Distributed Routed Backbone in Mixed IP/IPX Networks - After 3LS
Logical View:
VLAN 1
IP5, IPX5
FDDI
IPX6
WAN
IP1 IPX7
IP2
IP2, IPX 7
IPX4
IP4
VLAN 2
VLAN 3
FE
VLAN 5
VLAN 4
IP6
IPX5
IPX8
IP3,
IPX8
VLAN 2
IP1, IPX6
VLAN 6
IP23
Physical View
VLAN 1
IP1, IPX6
VLAN 2
IP2, IPX7
VLAN 3
IP3, IPX8
VLAN 4
IP4, IP6
IPX4
VLAN 5
IP5, IPX5
LEB-200
LSE-404S
LFE-4004
LSE-404S
LEB-200
LFE-100
LEB-200
LSF-100
LFE-4004
3LS
LEB-200
LEB-200
LSE-404S
LEB-200
V2, IP2
Fast Ethernet
Servers
LFE-100
FullDuplex,FEBackbone
LFE-4004
3LS
LSE-404S
VLAN 4
IPX4
WAN
V3
VLAN 6
IP23
router or off-load the router by acting as a front-
end.
• The 3LS switches traffic between IP/IPX subnets
(VLANs) at wire speed.
• Easy VLAN mapping of IP/IPX subnets
preserves segmentation.
• LANswitch has options for full duplex, Fast
Ethernet backbone (shown here), or a switched
FDDI backbone can be implemented.
• Fast Ethernet relieves server bottlenecks and
boosts client-server performance.

Page 28
5b: LANswitch to ATM Backbone in Mixed IP/IPX Networks - After 3LS
Logical View:
VLAN 1
IPX6IP1 IPX7
IP2
IP2, IPX 7
VLAN 2
VLAN 3
FEIPX8
IP3,
IPX8
VLAN 2
IP1, IPX6
IP5, IPX5
WAN
IPX4
IP4
VLAN 5
VLAN 4
IP6
IPX5
VLAN 6
IP23
ATM
ATM
ATM
Physical View
VLAN 1
IP1, IPX6
VLAN 2
IP2, IPX7
VLAN 3
IP3, IPX8
VLAN 4
IP4, IP6
IPX4
VLAN 5
IP5, IPX5
ATM Campus Backbone
LEB-200
LSE-808
LFE-4004
LSE-808
LEB-200
LFE-100
LSA+
LFE-4004
3LS
LEB-200
LEB-200
LEB-200
LSE-404S
LEB-200
Fast Ethernet Servers
LFE-4004
3LS
VLAN 4
IPX4
WAN
IPX5
LSA+
LEB-200
LEB-200
LEB-200
155 Mbps
Collage 740
V2, IP2
V3
VLAN 6
IP23
• LANswitch LSA+ modules provides standards-
based access to the Collage 740 ATM Campus
Backbone.
• The 3LS switches traffic between IP/IPX subnets
(VLANs) at wire speed.
• LANswitch LEB-200 full duplex, Fast Ethernet
modules create a high-speed collapsed backbone
in each building.
• Visage stackble switches deliver wire-speed
switching between Ethernet workgroups, servers
and power users.

Page 29
Appendix: IP/IPX plus other Network Protocols
The LANswitch 3LS Multilayer IP/IPX switch is designed to deliver wire-speed, low-latency switching
between IP/IPX subnets. In some networks, these protocol are used in conjunction with other routable
protocols such as DECnet and Appletalk, or non-routable protocols, such as NetBIOS and LAT. The goal
in designing a multilayer switching solution for these kinds of networks is to ensure that the non-IP/IPX
protocols are switched at Layer 2 by LANswitch, without compromising the Layer 3 switching
performance between IP/IPX subnets. The following sections discusses the optimum ways to configure
those protocols that are not routed by the LANswitch 3LS.
A simple configuration rule
When protocols other than IP/IPX are present in the network, logical and virtual segmentation of the
network becomes more of an issue. This simple, key rule always applies:
Configure the network such that all users of an unsupported protocol (for example, all DECnet users or
all NetBIOS users) are located in the same broadcast domain, in order to enable switching between them.5
If all unsupported protocols are configured in the same broadcast domain, LANswitch will switch packets
between the users of these protocols at Layer 2. While this solution is simple, it may be more efficient to
segment these users into separate broadcast domains per protocol (e.g., one domain for DECnet, one
domain for Appletalk, and so on). Then, each broadcast domain can be fine-tuned to handle the level of
broadcast traffic carried by the LAN.
Not covered
For network protocols other than IP and IPX, the LANswitch 3LS cannot be used as a router. It routes only
IP and IPX traffic. Hence the impetus to install a 3LS in the first place must come from the existence of IP
and/or IPX-based subnets. When other routable or non-routable protocols are also present in the same
LAN, LANswitch can provide unmatched Layer 2 switching performance for these protocols. As
mentioned earlier, this requires keeping these non-routable users in a flat logical network (same broadcast
domain), which could necessitate reconfiguration of a few end stations.
However, there are two instances in which LANswitch Layer 2 capabilities cannot provide the required
switching connectivity:
• When routing is required for unsupported, routable protocols due to the existence of different subnets.
For example, internetworking between separate DECnet areas can only be provided by DECnet
routers.
5
In a purely switched environment, the whole network constitutes one broadcast domain, while each
physical segment that is connected to a switch port constitutes a separate collision domain. Dividing this
single broadcast domain into several discrete broadcast domains is done by defining Virtual LANs - one
VLAN per domain.

Page 30
• When VLANs are configured such that users of an unsupported protocol become members of different
virtual LANs (For example, DECnet station 34 is on VLAN 1 and DECnet station 51 is on VLAN 2).
To provide connectivity between same-protocol stations located in different virtual LANs, the 3LS
provides a special bridging function between them. This is called VLAN bridging.
Recommended configuration for routable, but unsupported protocols (e.g.,
DECnet)
DECnet
The combination of DECnet v4 routers and LAN switches is tricky because a typical DECnet router
assigns the same physical (MAC) address to each one of its ports. In contrast, LAN switches do no support
duplicate MAC addresses. Each LANswitch port must have a unique MAC address. Therefore, for a given
DECnet router, only one port can be connected to the switched network.
DECnet routers operate on two levels and are used for a number of interconnectivity applications that are
unique to the DECnet protocol.
DECnet Router - Level 1
• Connects remote segments of the same DECnet area over a WAN link.
• Connect segments that are in the same DECnet area, but are physically separated.
• Supports alias naming in a “cluster” environment.
DECnet Router - Level 2
• Supports all Level 1 applications.
• Routes between different DECnet areas. Level 2 routers are mainly used to connect two or more
DECnet areas together across the WAN/public network.
When dealing with Level 1 routers used for a WAN link, we recommend that the DECnet router continue
to provide the WAN connection, while the LANswitch 3LS will handle the IP/IPX routing and DECnet
switching (remember, our target network is primarily based on IP/IPX, and DECnet comprises only a
small percentage of the network traffic).
When dealing with Level 1 routers used to connect physically separate DECnet segments, LANswitch
should be used as a direct replacement for the router because it provides a superior solution. Connecting
DECnet segments to the LANswitch hub creates a flat DECnet network where inter-segment traffic within
the DECnet area will be speedily switched at Layer 2. The IP/IPX traffic in this network will continue to
be switched or routed by the 3LS as necessary.

Page 31
One DECnet area spanning the campus
3LS
LSE-404S
WAN
LSF-100
DECnet 1
IP/IPX
IP/IPX
IP/IPX
3LS
LSE-404S
LSF-100
DECnet 1
IP/IPX
DECnet 1
IP/IPX
DECnet 1
IP/IPX
• DECnet area 1 comprises a single broadcast domain in which all traffic is switched at Layer 2.
• Immediate improvement in network performance
• Level 1 router handles traffic to remote DECnet segments.
1. DECnet router with one physical address - no VLANs
Assumption: There is one DECnet area and one LANswitch hub per building
For DECnet routers that allow only one physical address for all interfaces on the router, the best way to
utilize LANswitch for DECnet traffic is to configure all the DECnet nodes that are attached to the same
LANswitch hub, in the same DECnet area. This creates one flat DECnet network within the LANswitch
hub. If the campus network comprises many buildings, and the LANswitch hub in each building has its
own DECnet area, then we need some way for these different DECnet areas to communicate with each
other. One solution is to connect a DECnet router (Level 2) to each LANswitch hub and let the routers
forward packets from one DECnet area to another. Once again, intra-area traffic will be switched by
LANswitch at Layer 2, and inter-area traffic will be routed by the DECnet router at Layer 3.
Another option would be to configure one DECnet area across multiple LANswitches. The only
requirement is that the number of DECnet routers equals the number of DECnet areas in the network.
When one DECnet area spans many hubs, the router needs to be connected to only one of the hubs within
that area to handle area routing and WAN access requirements.

Page 32
Different DECnet area in each building of the campus network
IP/IPX
DECnet 1
IP/IPX
DECnet 1
IP/IPX
DECnet 1
3LS
LSE-404S
LSF-100
IP/IPX
DECnet 2
IP/IPX
DECnet 2
IP/IPX
DECnet 2
3LS
LSE-404S
LSF-100
IP/IPX
DECnet 3
IP/IPX
DECnet 3
IP/IPX
DECnet 3
WAN
DEC
Level 2 Router
DEC
Level 2 Routers
• One DECnet area per building
• Between separate segments within the same area, traffic is switched at Layer 2 by LANswitch.
• DECnet Level 2 routers provide inter-area connectivity and WAN access.
• DECnet uses “area-routers,” where traffic between areas travels between area-routers.
• One building remains as it was and continues to use its router for connectivity between same-area
segments, connectivity to other buildings (i.e., DECnet areas), WAN access, and to support other
applications as well.
2. Adding VLANs to routable protocols
Why should we configure VLANs at all? The main reason is that the IPX protocol requires it. Another
reason is broadcast control. By grouping a portion of the LAN users into a virtual LAN, we are able to
confine all broadcast traffic originating from those users to that VLAN group. In some cases, and
especially in switched networks, broadcast control is less important because the level of broadcast traffic on
the LAN is negligible or it does not adversely affect network performance.
However, when there is a lot of broadcast traffic that clogs up the LAN and reduces performance, virtual
LANs can be used to segment the switched network into separate broadcast domains, with each VLAN
representing a different domain.
For IP and IPX, which account for the majority of network connections, Madge recommends segmenting
the switched network (using VLANs) to the extent that adequately addresses the level of broadcast traffic
and enables the maximum amount of switching for all protocols. At one extreme, we could define a

Page 33
separate VLAN for each IP/IPX subnet. At the other extreme, we could put all put all IP subnets and IPX6
networks into a single VLAN, which would create one broadcast domain for all stations and is essentially
the same as having no VLANs at all. While both of these extremes are workable and wholly supported by
the 3LS, the optimum solution lies somewhere in between. The following guidelines should be considered
when deciding how to use VLANs to segment the switched network:
• The number of VLANs will depend on the size of the network. VLAN coverage should give you
flexible control of network traffic, reduce the level of broadcasts, and should not conflict with the
addressing schemes of other protocols present in the network. Specifically,
− Never divide a single Layer 3 protocol group into multiple VLANs (i.e., you cannot put the same
DECnet area into two separate VLANs)
− You should not divide non-routable protocol domains into multiple VLANs.
• By defining fewer VLANs, we can maximize Layer 2 switching for the protocols not supported by the
3LS.
• The number of VLANs will be equal to the number of different IPX networks you wish to define (one
VLAN per IPX network). This enables segmentation and switching of IPX throughout the corporate
network.
6
Configuring all IPX networks into one VLAN (broadcast domain) creates a flat IPX network.

Page 34
A VLAN Example: Multiple DECnet areas in the LAN
When VLANs are configured/required for the reasons we have discussed, it is possible to have a one-to-
one correlation between the DECnet area (comprising DECnet nodes and router ports), and the VLAN to
which all of its ports are assigned. Another possible configuration is to assign all DECnet areas to the
same virtual LAN, however, the feasibility of this option depends on the configuration of other protocols in
the LAN and the level of broadcast traffic in the DECnet network. The optimum solution probably lies
somewhere in between, in which 2 or more DECnet areas are combined into a single VLAN. In this way,
effective broadcast control can be achieved using fewer VLANs. The result is a network that is simple and
easy to manage.
In any case (i.e., one-to-one VLAN/area correlation, one-to-all VLAN/area correlation, or somewhere in
between) the DECnet router continues to forward internetwork traffic, while LANswitch switches the
intranetwork traffic. When there is a one-to-one correlation between DECnet areas and VLANs, the
LANswitch 3LS will perform VLAN bridging, and the DECnet routers will perform all routing functions.
Example 1: Multiple DECnet areas - one or multiple VLANs
3LS
LSE-404S
LSF-100
IP, IPX
DECnet 1
IP/IPX
DECnet 1
IP/IPX
DECnet 1
3LS
LSE-404S
LSF-100
IP, IPX
DECnet 2
IP/IPX
DECnet 2
IP/IPX
DECnet 2
Area
Router
V2
VLAN 1 VLAN 1 or VLAN 2
Area
Router
V1
• When both DECnet areas are in the same virtual LAN (VLAN 1), the DEC area-routers will route
traffic between area 1 and area 2.
• When each DECnet area belongs to a different virtual LAN (VLAN 1 & VLAN 2), routing between the
DECnet areas and VLAN bridging between the routers is required.

Page 35
Example 2: Multiple DECnet areas - multiple VLANs - area routers are linked
3LS
LSE-404S
LSF-100
IP, IPX
DECnet 1
IP/IPX
DECnet 1
IP/IPX
DECnet 1
3LS
LSE-404S
LSF-100
IP, IPX
DECnet 2
IP/IPX
DECnet 2
IP/IPX
DECnet 2
Area 1
Router
Area 2
Router
VLAN 1 VLAN 2
Router
Link
V1 V2
• Each DECnet area is assinged to its own VLAN.
• In this topology, no VLAN bridging will occur because the inter-area DECnet traffic travels via the
router link.
Recommended configuration of VLANs for routable and non-routable
protocols in a flat network (no routing required)
1. Flat network and flat VLAN
The wire-speed bridging functionality that LANswitch provides at Layer 2 maximizes performance of the
network. Therefore, to obtain optimum performance metrics and to keep the network configuration simple
and easy to manage, we should configure the network for Layer 2 switching (rather than VLAN bridging)
wherever possible.
One of the ways to make this possible is to configure all users of unsupported and non-routable protocols
as members of the same virtual LAN. By defining one VLAN for everybody, we create a “flat” virtual
network where traffic between users is switched (very much like the flat physical network, but without
being dependent upon physical connections, and having as many collision domains as needed). While this
configuration is easier to manage and maintain, it may not be possible due to conflicts with other protocol
and network requirements. For example, due to the limitations of IPX, a virtual LAN can have only one
IPX network associated with it. If DECnet and NetBIOS stations happen to be on the same LAN segments
as IPX stations, and the IPX networks require different broadcast domains, those segments cannot be
configured in the same VLAN.

Page 36
3LS
IPX2
NetBIOSDEC3
IPX1
VLAN 1
A B
DEC3
3LS
IPX1
NetBIOS
DEC3
IPX1
VLAN 1
A B
DEC3
IPX3
C
IP3
VLAN 2
Figure 15: Switch ports A and B may not be
configured in the same VLAN because only one
IPX network per VLAN is allowed
IPX1 and IPX2 have been consolidated into a
single IPX network. Now, switch ports A and B
are assigned to one VLAN which also includes
all DECnet stations.
If these kinds of conflicts exist, the single-VLAN solution will not work. One alternative is to re-evaluate
the IPX network segmentation. It could be preferable join the conflicting IPX networks into a single IPX
network/VLAN. This enables most of the traffic to be switched at Layer 2.
Another alternative which would keep most of the traffic switched, is to configure a separate VLAN for
each unsupported protocol. This would mean that all DECnet users would belong to one VLAN; all
Appletalk users would belong to another VLAN; all NetBIOS users would belong to a third VLAN; and so
on. This solution might require the network manager to physically move some end-stations from one
segment to another, but since these protocols comprise a minority of stations on the network, the number
of moves should be few.
3LS
IPX2
NetBIOSDEC3
IPX1
VLAN 1
A B
VLAN 2
DEC3
Figure 16: Putting each non-supported protocol in a separate VLAN enables switching within the
protocol group

Page 37
2. Flat network and segmented VLANs
As mentioned above, it is preferable to place each protocol in its own VLAN. However, there may be
networks where this is not possible, and therefore we might have to configure multiple VLANs for a given
protocol. Consider a DECnet area that has 1024 stations (the legal maximum). The IS manager might be
compelled to segment the DECnet area into two or more VLANs, where some stations are on VLAN 1,
some stations are on VLAN 2, and so on. This creates different broadcast domains, which means that the
different VLANs will not be able to communicate without the aid of a VLAN bridging device.
In these cases, the LANswitch 3LS will “bridge” between users of the same protocol who are located on
different VLANs. In order to use VLAN bridging across multiple switches, a 3LS module must be installed
in every LANswitch hub.7
that requires bridging services. Normally, one 3LS module is sufficient to
provide routing services for multiple LANswitch hubs. But when VLAN bridging is employed, a 3LS
module must be installed in each hub.
When the LANswitch 3LS operates in VLAN bridging mode (bridging enabled), it will bridge one and
only one of the following:
1. DECnet and LAT
2. NetBIOS
3. Other non-routable protocols
7
Applies to inter-switch link based on LANswitch LEB-200, LSF-100, and LSA+ backbone modules.

Page 38
6: Collapsed Routed Backbone in ALL Protocol Networks
Logical View: Before Logical View: After LANswitch 3LS
IP/IPX
WAN
NetBIOS
IP
LAT
Terminal Server
IP/IPXDECnet
IP1/IPX6
NetBIOS
LAT
Terminal Server
IP2/IPX7
DECnet
WAN
IPX 6
IPX2
VLAN 2
VLAN 1
VLAN 3
VLAN 4
VLAN 4
IP3
IP/IPX
ALL
WAN
IP/IPX
DECnet
LAT
IP
NetBIOS
VLAN 1
IP1
IPX6
WAN
VLAN 3
NetBIOS
IP
ALL
3LS
LSE-404S
LFE-4004
V2
V1
V4
V3
VLAN 2
IP2
IPX7
VLAN 4
DECnet
LAT
V2, IPX7
V1, IPX6
LSE-404S
VLAN 4
• Enterprise network is predominantly IP/IPX,
with some stations running other protocols.
• Protocol-specific routers needed in some cases,
such as DECnet.
• Network expansion is limited by the number of
router links and router capacity.
• Each non-routable protocol is configured in a
separate VLAN, enabling Layer 2 switching
between same-protocol users.
• The VLAN configuration of the router depends
on what kind of services it provides
• No VLAN bridging performed in this example
(only routing).

Page 39

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Madge, the Madge logo, Cellenium, LANswitch, and Visage are trademarks, and in some jurisdictions may be registered trademarks, of Madge Networks or its affiliated companies.
Other trademarks appearing in this document are the property of their respective owners.
© Copyright 1996 Madge Networks. All Rights Reserved.
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Madge LANswitch 3LS Application Guide

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Madge LANswitch 3LS Application Guide