A/B Copper Network Backup Switches – A Complete Design Guide

However simple the term A/B switch may sound, A/B switches are not necessarily simple to design. Following is a thought process with examples that can assist any network manager with the development of the exact switch to meet his or her requirements.

1. Location – Where are you going to put the switch?:
A) Desktop – A desktop A/B switch may look like a black box with a knob, but that is not the total story. An example is the Model 8050 RJ45 A/B Switch that is CAT5 compliant. This manual switch enables access to two 10/100 Base-T networks (up to 100 Mbps) and incorporates a high-quality sealed switch with self-wiping low-impedance contacts. The switch is transparent to data speed and format. The anodized enclosure provides EMI/RFI shielding which enables the switch to perform well in noisy environments. A desktop switch can be compact, full-featured and sit right on a desk.

B) Computer Room Rack – Following are two examples of rackmount A/B switches.
i. Switch Modules – Model 9740 switching system includes switch modules and a rack that can accommodate up to 40 channels in only 8.75 inches of panel height. The A, B and COMMON connections are on the rear panel. The 2-position rotary switches are neatly lined up on the front panel. All 8 pins are switched which allows compatibility with all RJ45 interfaces. Systems are available to accommodate both CAT5 and CAT5e high-speed requirements. Forty channels of A/B switching in a compact rack may meet your business requirements.

ii. Switch Box – A switch box instead of a module may be a better fit for some requirements. The Model 9716 16-Channel RJ45 CAT5e Compliant A/B Switch, with manual operation, fits into a standard 19″ rack (2U high). Sixteen front-panel knobs provide individual control of each channel. This switch configuration is rated for 10/100/1000 networks (up to CAT5e).

C) Process Control System – DIN rail mounting is an ideal method of mounting switches for use in process control systems. The Model 9080 RJ45 A/B/Offline Switch allows the user to access two RJ45 devices connected to its A and B ports with one RJ45 device connected to its COMMON port, or to isolate all ports by switching to the OFFLINE position. This unit is a manually operated keylock switch requiring no power. The switch is easily integrated as a system component by utilizing its rear panel DIN rail mounting bracket. A grounding screw is mounted on the front panel.

D) Nuclear Power Plant or other Rough Environments – The Model 4503 is a Seismic-Proof DB9 A/B switch. This manual switch has been ruggedized to withstand vibrations. The switch and its feed-through connector have successfully passed the rigorous seismic testing of the Electric Power Research Institute (EPRI) Seismic Qualification Reporting and Testing Standardization SQURTS Program, qualifying it for use in nuclear power plants. The Model 4503 is ideal for factory floors, energy facilities, and any other harsh environment application.

E) Ship or other Mobile/Motion Application – The manual Model 4504 Ruggedized DB25 A/B switch is designed to withstand vibrations encountered in mobile and motion applications. This switch has also passed rigorous seismic testing. The optional mounting ears allow firm attachment.

F) In the Wall – The Model 7190 is a manually operated double gang wall box Online/Offline switch. When in the ONLINE position, the switch connects the COMMON device to Device A. In the Offline position, the switch disconnects the COMMON device from Device A. There are two RJ45 CAT5e ports on the bracket inside the wall box. The RJ45 network cables must be run into the box and bracket before installing in the wall.

2. Connectors – Types of Connectors/Ports
The common types of connectors and ports include: DB9, DB15, DB25, DB37, HD15, BNC, RJ45, RJ11/12, MINI-DIN and USB.

3. RJ45 Connector/Port – If the switch has RJ45 ports, is CAT5, CAT5e, or CAT6 required?
A) Cat5 is a type of twisted pair cabling. Twisted pair cabling is categorized according to its transmission capability. Category 5 (CAT 5) cabling transmits data at speeds up to 100 Mbps.
B) Cat5e is a variation of CAT5 that supports short-run Gigabit Ethernet (1000 Mbps) networking by utilizing all four wire pairs in a CAT5 cable.
C) CAT6 is a cable standard for Gigabit Ethernet and includes stringent specifications for crosstalk and system noise. The CAT6 cable standard provides performance of up to 250 MHz and is suitable for 10BASE-T, 100BASE-TX (Fast Ethernet), 1000BASE-T/1000BASE-TX (Gigbit Ethernet) and 10GBASE-T (10-Gigabit Ethernet). Most high quality CAT6 cables will exceed the standard and actually provide performance of up to 550 Mhz.

4. Controls – How do you want to control the switch?
Our four categories include: Local Manual, Remotely Controllable, Automatic, or any combination.

A) Local Manual – All of the network switch examples above are manually operated. They can feature pushbuttons or rotary knobs and they require no power.

B) Remotely Controllable Network Switches – This switch group includes RS232 Serial Control, Contact Closure, IP Addressable, and any combination of the three.

i. RS232 Serial Control – The REMOTE connector accepts RS232 serial data ASCII commands. An example of a switch with RS232 Serial Control is the Model 7356 6-Channel RJ45 CAT5 A/B Switch with Local and Remote Individual Channel Control. Each channel maintains its current position in the event of a power loss and continues to pass data. The unit fits into a standard 19″ rack and is 1U high. The Supervisory Remote Port consists of a DB9 female connector that accepts RS232 serial data. Switch positions can be selected locally via front panel controls or remotely via RS232 ASCII command via the Remote port.

ii. Contact Closure – An example of a Contact Closure switch is the Model 7359 Tri-Channel RJ45 CAT5 A/B Switch with Remote Control via Contact Closure. The switch is controlled manually via pushbuttons or remotely via the DB9 female connector on the rear panel that accepts contact closure signal switch commands.

iii. IP Addressable – An example of an IP Addressable switch is the Model 7465 8-Channel RJ45 A/B Switch with 10/100 Base-T LAN TELNET access. The 8 channels on this switch can be independently controlled via pushbuttons. Remote access can be accomplished via the RJ45 Female connector on the rear panel that accepts 10/100 Base-T LAN Access Ethernet for remote control operation. Remotely select switch position, query switch position, and lockout the front-panel pushbuttons. During power loss, the Model 7465 continues to pass data in the lost position.

iv. Graphical User Interface (GUI) – The remote GUI interface allows the user to control the switch remotely with simple point and click operation. The Model 7358 RJ45/48 T1 Interface A/B Switch features both Telnet and GUI remote control. This switch allows quick connection to any one of two RJ45/48 T1 interface devices from one COMMON device. Local control is via a front-panel pushbutton. The remote control RJ45 port is an IP addressable, 10/100 Base-T port. Remote control Telnet command interface or the Graphical User Interface allow the user to control the switch position, lockout the front panel operations and obtain switch status. The software features allow the user to access the switch via any standard Web browser. With simple point and click operation the user can control and monitor the Model 7358. The user can also change the switch’s IP address. LAN access gives users across the LAN or over the Internet access to control the switch.

v. Code Operated – The switch position and lockout status can be changed through the data stream on the COMMON port. The Model 4406 RJ45 Code-Operated A/B Switch shares one RJ45 interface device between two other devices. The switch may be controlled via a front-panel pushbutton or remotely by sending a trigger character sequence to the unit via the Remote port. Switch position status is displayed by front-panel LEDs or can be queried by the PC connected to the Remote RS-232 serial port.

5. Security Concerns – Keylock, Lockout and Offline Positions
A) Keylock – The advantage of a keylock is the security of knowing that only the person with the key can change the switch position. The Model 8076 Dual-Channel RJ45/110-Block, CAT5e 100 Base-T Network Access Keylock Switch accepts two 8-conductor CAT5e cables INPUT via two RJ45/110-Block punch-down connectors. This switch allows the user to switch-through or break-from two OUTPUT RJ45 exit ports. The user can remove the top cover of the switch and punch down the connections inside the unit.

B) Lockout – The advantage of the lockout feature is that the user can lockout the switch position remotely and be assured that the switch is operating as prescribed. The Model 7348 Tri-Channel RJ45 CAT 5 A/B Switch may be controlled manually via pushbuttons or remotely from an RS232 serial port. Each channel is an individual switch that is independently controlled. Remote commands can switch each channel individually or all channels simultaneously as well as lockout the front panel control. Remote commands allow monitoring of channel switch position and lockout status.

C) Offline and Cutoff Positions – With remote and automatic switches, the switch can automatically switch to an offline position before switching between ports A and B. Manual and remotely controllable switches are also available with a physical offline position that can be selected to stop the switch from passing data. The Model 7246-ESL Dual Channel RS530 Switch and RJ45 Secure/Non-Secure Switch with Cutoff position provides two-channel switching in a low profile, 19-inch 1U rack unit. Channel one shares a single DB25(M) interface device connected to the COMMON port among two other DB25(F) devices connected to the SECURE and NON-SECURE DB25 ports. Channel two shares an RJ45 device connected to the COMMON port among two other RJ45 devices connected to the SECURE and NON-SECURE RJ45 ports. Both channels allow the user to set the switches to the CUTOFF position which stops any and all data throughput for the switch. If power to the Model 7246-ESL is removed, both switches will automatically move to the CUTOFF position. When power is restored, each switch will move to the programmed default position.

6. Power Loss – How do you want to handle a power loss?
Which position should the switch be in? Should the switch continue to pass data?

A) Last Position, Pass Data – The Model 4421 CAT5 RJ45 A/B Switch with Password Serial Remote Port includes an RS232 serial security enhanced Supervisory Remote Port requiring a password login to access. Upon proper authentication, a terminal or computer in terminal mode connected to this port can communicate with the unit, determine its status, change the switch position as desired, and/or lockout the front panel switching capability. The Model 4421 retains the last switch position in the event of a power loss and continues to pass data.

B) Default Position – The Model 4515 8-Channel A/B Single Contact Relay Port Switch, RJ11 Interface with 10/100 BASE-T LAN Access and Serial Remote Access shares a device connected to a single pin of each RJ11 interface port between two other devices connected to the A and B pins for each port. Remote access can be via a Web-based GUI interface through 10/100 BASE-T Ethernet connection or using ASCII commands sent to the unit via an RS232 connection. Each port has (4) active contacts: Normally OPEN, Normally CLOSED, the WIPER contact of the relay, and a pin for SG (signal ground referenced to the switch unit). The Model 4515 defaults to the Normally CLOSED position in the event of a power loss to the unit.

C) Switch Evaluates and Determines Power Up Position – The Model 7387 RS232 DB25 A/B Switch with Fallback and Remote Port shares a single port interface device connected to the COMMON port among two other devices connected to the A and B ports. This switch can sense RD activity or DCD presence on the ports and switch accordingly. The switch can also be controlled manually via pushbutton or remotely via contact closure. All switched signals are passed via latching copper contact relays that maintain their position and continuity in the event of a power loss. When power is restored, the Model 7387 loads the previous position and mode of operation and checks DIP switch settings and the remote port to determine the correct startup configuration.

7. Number of Channels per Chassis – From single channel A/B switches to multiple channel switches, the technology exists to handle specific requirements.

A) Combining Single Channel Switch Modules – Up to eight single-channel Model 7009 RJ45 CAT5e A/B/Off-Line Remotely Controllable Switch Modules compactly fit into a Model 9030 Rack. This modular expandable system allows the user to add switching capacity as required. Channels are switched individually.

B) 4 Channels in Slim Rackmount Configuration – The Model 7234 Quad-Channel RJ45 A/B Switch with Remote Control Port is slim, only 1U high, and fits into a standard 19″ rack. All four channels are switched simultaneously. This switch allows local switching via pushbutton. Remote switching is accomplished via the transition from open to closed or closed to open via a single set of contacts connected across pins 1 & 2 of the DB9/Female REMOTE connector port. Upon initial power to the unit, the unit will read the REMOTE port to determine the power up position state. If there are no connections to the REMOTE port connector, pins 1 & 2 are open, thus the unit will default to all four channels in the A position. All four channels are switched simultaneously.

C) 8 Channels in a Rackmount Configuration – Model 9066 8-channel RJ45 (2 Pair) 10BASE-T manual A/B Switch enables access to two 10 Base-T networks. The operator can reroute data between two networks with a simple push of a button. Switch each channel individually.

D) 16 Channels of Auto-Controlled Switching in Rackmount Configuration – The Model 7435 Auto-Controlled 16-Channel RJ45 A/B Switch system allows sharing a single port RJ45 interface device connected to the COMMON port among two other devices connected to the A and B ports for each of the switch’s 16 channels. The port position, A or B, of individual channels in the Model 7435 is user-configurable to be determined either manually, via the GUI, or automatically per the programming. In the Automatic mode, the position of the individual channels is controlled by sensing incoming data on ports A and B. All switched signals are passed via gold clad silver relays that maintain their position and continuity even in the event of a power loss. All channels can be switched simultaneously or independently.

E) Up to 40 Channels of A/B Switching – Model 9741 handles up to 40 channels of A/B switching in a high-density switch system that takes up only 8.75 inches of panel height. The A, B and COMMON connectors are on the rear panel. The 2-position rotary switches are on the front panel. All 8 pins are switched allowing compatibility with all RJ45 interfaces. This reliable switch system is manually operated and requires no power. Each channel is switched individually.

8. Channel Control – Simultaneous, Individual Remote Control or Both. How do you want to switch your channels?
The examples above provide a variety of control systems:
Model 7009: Individual switching
Model 7234: Simultaneous switching
Model 9066: Individual switching
Model 7435: Individual or simultaneous switching
Model 9741: Individual switching

9. Power Requirements
Most remotely controllable and automatic switches require an external power supply.
A) UL approved 120VAC, 60Hz wall mount power module that supplies 12 VDC, 500mA to the unit.
B) CE and UL listed wall mount wide range power module, 100VAC, 240VAC, 50Hz/60Hz supplies 12 VDC, 1.5A to the unit.
C) Exceptions: Some switches require customer supplied voltage to the power input connectors.

10. Summary
The data networks of today are almost as diverse as snowflakes. Managers have huge tasks: trying to backup data, secure the network, deal with fiber to copper conversions and so much more. This white paper was developed to be used as a guide to help in the design of an A/B copper network backup switch.

How to Determine the Right Fiber Optic Network Backup Switch For Your Application

1. Questions to Consider in the Design of Your Switch.

A. How many positions does your application require?

i. Two-position and three-position switches are very common. Complex multi-position switches are also required.

B. What type of connector or port preference? The selection of connectors include ST, SC, LC, ESCON and others.

i. ST connectors use a plug and socket that is locked in place with a half-twist bayonet lock.

ii. SC connectors feature a push-pull latching system providing speedy insertion and

removal along with a positive connection.

iii. LC connectors are smaller versions of the SC connectors.

iv. ESCON connectors have two 2.55 mm ceramic ferrules and a robust strain relief design.

C. Fiber Requirement: Simplex or Duplex?

i. In configuring your backup switch, a determination on the fiber type, simplex or duplex needs to be made.

1. Simplex fiber optic cable consists of a single fiber, and is primarily used in applications that only require one-way data transmission. Simplex fiber is available in both singlemode and multimode. Simplex means the cable has only one thread of fiber optic glass inside the single core and one single outer jacket.

2. Duplex cable consists of two fibers, usually in a zipcord (side-by-side) style. Duplex multimode or single mode fiber optic cables are used for applications that require simultaneous, bidirectional data transfer. Workstations, fiber switches and servers, fiber modems, and similar hardware usually require duplex cable. Duplex fiber is available in singlemode and multimode. Duplex fiber cable can be regarded as two simplex cables having their jackets joined by a jacket material. Some duplex fiber optic cables have clips on the two fiber optic connectors at each side of the cable to combine the two connectors together.

D. Mode: Multimode or Singlemode?

i. Multimode fiber optic cable has a large diameter core that is much larger than the wavelength of light transmitted, and therefore has multiple pathways of light. Several wavelengths of light may be used in the fiber core. Multimode optical cable is most commonly used for shorter distances, such as a building or a campus. Typical multimode links have data rates of 10 Mbit/s to 10 Gbit/s over link lengths of up to 600 meters.

ii. Singlemode fiber optic cable has a small core and only one pathway of light. With only a single wavelength of light passing through its core, singlemode realigns the light toward the center of the core instead of simply bouncing it off the edge of the core as with multimode. The glass fiber diameter is usually 8.3 to 10 microns. Single mode fiber provides a higher transmission rate and up to 50 times more distance than multimode.

E. Switch Specifications: Wavelength, Speed, Fiber Size, Simplex, Duplex, Interface Conversion will be unique to your network. Examples of two switches with very different specs follow.

F. Technology Preference: All Optic, Optic/Electronic/Optic, No Preference?

i. All-Optic (O-O-O) – Fiber optic network switches designed with scalable all-optical, O-O-O, MEMS (Micro-Electromechanical System) technology employ control mechanisms to tilt mirrors or direct prisms in multiple directions to manage light signals without converting the signals to electrical and back to optical. This increased level of control minimizes insertion loss and keeps the features of high data rate and protocol transparency.

ii. Optic/Electronic/Optic (O-E-O) Technology – Optic/Electronic/Optic technology is both economical and reliable, however such an architecture prevents the switch from performing with the same speed as an all-optical scheme and is not transparent to network protocols used.

G. Chassis Type: Rackmount or Desktop? – This table lists a variety of switches built to fit equipment racks and desktops.

H. Security Concerns can be addressed in a variety of ways.

i. Off-line positions.

1. External Off-line Position – The block diagram of the Model 4192 Fiber Optic SC Duplex A/B/C/D/Off-Line Switch illustrates a fiber optic switch with an external off-line position. This switch enables a fiber optic device connected to the SC Duplex COMMON connector of the unit to access any of the four fiber optic networks connected to the A, B, C, or D ports, or to disconnect completely from all output ports. The switch position can be changed via a pushbutton or via a device connected to the Remote port. Applying the appropriate voltage to the designated pins of the Remote connector will cause the switch to change position.

2. External Off-Line Position with Switch Position Memory – The Model 4196 4-Way All-Optic Fiber Switch, Multimode, 62.5/125 Microns with a Fully Decoupled Off-Line Capability allows a fiber optic device connected to the unit’s SC Duplex COMMON connector to access any of the four fiber optic networks connected to the A, B, C, or D ports, or to disconnect completely from all output ports. Switch position can be changed via front-panel pushbuttons or by a device connected to the rear panel Remote port. Applying appropriate voltage to designated pins of the Remote connector also changes the switch position. The Off-Line pushbutton uncouples all fiber ports from each other. The Model 4196 has Switch Position Memory. When power is lost, the Model 4196 automatically changes to the Off-Line position and decouples all fiber connection in and out of the unit. When power returns, the Model 4196 automatically reads the voltages on the Remote port and looks to the pushbutton activity to select its switch position.

3. Internal Off-Line Position with Options − The Model 6275 ST Duplex Fiber Optic 8-Position Switch with Off-Line Position and Remote Serial Control provides both an Off-Line position and a keylock to lock out the front panel pushbutton controls. The Model 6275 features both local and remote control. The Off-Line position is a valid state to preserve network and data isolation. The user can configure the switch to either maintain its position and data pathways on power failure or to revert to the Off-Line position during power failure. A key is provided to lockout the front-panel pushbutton controls.

ii. Front Panel Lockout – The Model 6293 Fiber Optic Mirror A/B/C Switch, Single Mode LC Duplex with Remote Serial Access allows sharing a fiber optic LC duplex pair connected to the COMMON port among three other sets of LC duplex pairs connected to the A, B, and C ports with local and remote access functionality. The front-panel pushbutton can be locked out using remote ASCII commands.

iii. PassWord Protection – Password protection is another method of providing network security. The Model 4185 Fiber Optic SC Duplex, Multimode Switch/Converter allows accessing two separate fiber optic 100 Base FX ports (ports A and B) from a 100 Base TX Fast Ethernet port (COMMON port). The fiber optic/twisted pair copper conversion is built in. This unit includes an RS232 serial security enhanced Supervisory Remote Port. Upon proper authentication, a terminal or computer in terminal mode connected to this port can communicate with the unit, determine its status, change the switch position as desired, and/or lock out the front panel switching capability. A modem can also be connected to this port to remotely access the switch. Access to the Supervisory Remote Port feature is password protected.

I. Power Loss − How should your switch function during a power loss?

i. Should the switch continue to pass data?

ii. If passing data during a power loss, should data pass through the last selected switch position or go to the default position?

iii. Upon power up, should the switch remain in the last position or start up in default mode?

J. Number of Channels per Chassis – Electro Standards manufactures fiber optic backup switches ranging from Single-Channel to 16-Channel Switches.

K. Multiple channel switch control: Simultaneous or Individual.

Examples of how these switches function follow:

i. Simultaneous Channel Switching:

ii. Individual Channel Switching: All channels are switched individually with the

2. Putting the Switch All Together

3. Summary – Fiber optic switches of various functions are available to add versatility, improve efficiency, and enhance scalability of data networks. They may be operated locally by pushbutton or remotely via a variety of common communication interfaces. The agility that they add to network operational performance is limited only by the innovation of the user and the design expertise of the switch product provider.

Applications include switching to backup data lines, to test equipment, to monitoring equipment, or simply switching to off-line for security. Electro Standards Laboratories is available to provide an optimum switch solution for your application.

What Is an Ethernet Switch?

An Ethernet switch is a networking device that is used in almost all data networks to provide connectivity for our networking devices. Prior to the invention of the Ethernet switch, our Ethernet data networks used either Repeaters or Hubs to build Local Area Networks.

Before Ethernet Switches, a lot of networks used coaxial cable for local network connections, in a network topology that became known as a bus network. The most common bus networks used two early Ethernet cabling standards, which were the 10Base5 and 10Base2 coaxial cable standards. The 10Base5 networks were often referred to as Thicknet, while the 10Base2 networks were known as Thinnet. All network devices such as computers and servers were connected to a segment of cable in what was known as a “shared environment”, or more commonly a collision domain. This type of network relied on data being broadcast across the media to all connected devices.

The invention of the hub made it easier for devices to be added or removed from the network, but an Ethernet network using a Hub was still a collision domain, where collisions were way of life. Ethernet network interface cards were designed to use CSMA/CD and detect and deal with collisions. Unfortunately collisions do have an effect of slowing down a network and make that network less than efficient. A Hub is said to be a Layer-1 device as it has no real intelligence, and in fact it is really just a multi-port repeater, with data entering one port being duplicated when sent out the other ports. The reference to Layer 1 is to the bottom layer of the OSI 7 Layer reference model.

The Hub was eventually replaced by the Ethernet switch as the most common device in Local Area Networks. The switch, which is a much more efficient device, is said to be a more intelligent device than a Hub because it is able to interrogate the data within the Ethernet Frames, whereas a hub just retransmits the data. With Ethernet, we use 48-bit MAC Addresses when labelling specific physical network interfaces, and an Ethernet frame of data contains both the Source and Destination MAC Addresses to enable data to be routed and switched from one specific physical interface to another.

An Ethernet switch has 3 main functions, which are:

Address Learning

Forwarding and Filtering

Loop Avoidance.

Address Learning

When a data frame enters through a port on a switch, the Ethernet Switch reads the Source MAC Address and adds that address to a MAC Address Table. This table is often referred to as Content Addressable Memory (CAM). Within the table the MAC Address is associated with the physical port on the switch to which the network device is attached. The switch now knows which port to forward data to when an Ethernet frame arrives from elsewhere in the network, because it checks the destination MAC Address, and looks for a match in the table. The Destination MAC Address is therefore used by the Ethernet Switch to forward data out of the correct port to reach the correct physical interface.

Forwarding and Filtering

When a switch receives an Ethernet frame, it will read the Destination MAC Address in order to determine which port to forward the data out of. When a switch receives an Ethernet frame with a Destination MAC Address that is not referenced in the table, it floods that frame out of all ports in an attempt to reach the correct physical interface. If the correct device responds, then the switch will now know where that MAC Address resides, and is therefore able to add that address to the table for future reference.


Almost all modern switches run a protocol known as the Spanning-Tree Protocol, or STP. STP was originally a proprietary protocol developed by DEC, but is now an IEEE Standard known as IEEE 802.1d, which was later revised to IEEE 802.1w (Rapid Spanning-Tree Protocol). The role of Spanning Tree is to detect and manage loops in a network, which can be a big problem by allowing duplicate frames to be delivered, and cause the MAC Address Table to become unstable. In severe cases network loops will cause a network to be over subscribed and eventually be overwhelmed by the amount of data. Spanning-Tree allows network designers to build redundancy and resilience into a network, safe in the knowledge that any physical or logical loops created will be managed by the Spanning Tree Protocol.

You will hear the terms Layer 2 and Layer 3 Switch, what do they mean?

A Layer 2 Ethernet switch operates by performing like we described in the previous paragraphs. The Layer 2 name comes from the fact that it operates at Layer 2 of the OSI 7 Layer Reference Model. This Layer is often referred to as the Data-Link Layer, and it is the layer that Ethernet is described, and where MAC Addresses are used.

So what is a Layer 3 Ethernet Switch?

A Layer 3 Ethernet Switch combines the features and functions of a basic Layer 2 switch, with features normally associated with a Router. In fact, it is probably easy to describe a Layer 3 switch as a switch and a router combined. A Layer 3 switch will have either a number of fixed Ethernet ports that have layer 3 IP Addresses associated with them, or more commonly, configurable ports that can be Layer 2 or Layer 3 as desired. All but the smallest home consumer Layer 2 switches allow the configuration of VLANs (Virtual Local Area Networks), but are not able to directly route traffic between multiple VLANs. In order to do this, the addition of a Layer 3 device such as a Router would be needed. A Layer 3 switch can perform this function in addition to tradition Layer 2 switch functions.

When purchasing an Ethernet switch, you need to determine what its role will be in the network, and whether or not Layer 3 functions will be required. Normally a Layer 3 Ethernet switch will be more expensive than a comparable Layer 2 device, so it would be an unnecessary expense to employ a Layer 3 switch when a Layer 2 switch would suffice.

Ethernet switches have evolved since the first simple devices were introduced, and some have a lot of additional features and support a wide range of ever increasing network protocols. Some of these features and protocols will be discussed in future articles.