Networking Devices - Introductory Summary

7/28/2019 Networking Devices - Introductory Summary

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A White Paper on

Networking DevicesAnd Components

Adie Josh (Aditya Joshi)

Adapted from an Academic Assignment Report


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Networking Devices

And Components


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Index

Introduction 4

Hub 5

Repeater 7

Switch 8

Bridge 10

Router 11

Gateway 13

Brouter 15

Multilayer Switch 16

Network Interface Card 17

Modem 18

Firewall 19

Load Balancer 20

Proxy Server 21

Protocol Converter 21


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Since the advent of computer age, a new need started sprouting up. Data needed to be

transferred between devices, between universities and military establishments. By 1960s,

techniques were developed to efficiently route telephone calls through already existing

telephone networks. Meanwhile the concept of packets was under development. By 1969,

the Advanced Research Projects Agency Network (ARPANET) was built as the world's first

operational packet switching network and the core network of a set that came to compose the

global Internet. The network was funded by the Advanced Research Projects Agency

(ARPA) which later evolved into the Defense Advanced Research Projects Agency

(DARPA) of the United States Department of Defense for use by its projects at universities

and research laboratories in the US.

Rise of newer systems required newer devices. Machines needed devices to help them

translate and transmit the messages over regular telephone lines. Computers directlyconnected to other computers needed separate kind of hardware and communication medium.

These needs brought us to a totally new range of electronic devices. Digital switching and

routing devices started to be developed to facilitate communication through vastly growing

networks of computers.

Today, computer networks are the core of modern communication. All modern aspects of the

public switched telephone network (PSTN) are computer-controlled, and telephony

increasingly runs over the Internet Protocol, although not necessarily the public Internet. The

scope of communication has increased significantly in the past decade, and this boom in

communications would not have been possible without the progressively advancing computernetwork. Computer networks, and the technologies needed to connect and communicate

through and between them, continue to drive computer hardware, software, and peripherals

industries. This expansion is mirrored by growth in the numbers and types of users of

networks, from the researcher to the home user.

There is a vast array of Networking Devices and components available in the market. Their

applications depend on the use we desire to make of them. Many of them are ambiguous in

terms of their use in trivial situations. Many modern devices can perform the jobs of other

devices as well. They come in different configurations. You can buy a router for Rs. 5000/-

for home use and other one costing in lacs to be used in large networks and ISPs.

This white paper provides an insight into mostly used networking devices and components. It

also discusses their features, working and variants available in the market.


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Hub

Hub is a simple layer 1 device used in ComputerNetworks. It is used for connecting multiple Ethernet

devices together and making them act as a single

network segment. It has multiple input/output (I/O)

ports, in which a signal introduced at the input of any

port appears at the output of every port except the

original incoming. A hub works at the physical layer

(layer 1) of the OSI model.

A hub is a small rectangular box, often made of

plastic, that receives its power from an ordinary walloutlet. A hub joins multiple computers (or other

network devices) together to form a single network

segment. On this network segment, all computers can communicate directly with each other.

Ethernet hubs are by far the most common type, but hubs for other types of networks such as

USB also exist.

A hub includes a series of ports that each accept a network cable. Small hubs network four

computers. They contain four or sometimes five ports, the fifth port being reserved for

"uplink" connections to another hub or similar device. Larger hubs contain eight, 12, 16, and

even 24 ports.

Hub

Purpose: ConnectingEthernet devicesActing Layer : 1Commercial Examples :

D-Link DE-805TP 1538 Series Micro Hub


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Features in Commercial Models

Modern hubs like DLink 1008 provide upto 16Gbps forwarding capacity, which is more than

enough for general use. It is a store-and-forward device and provides a buffer memory of

1Mb for every device connected to it.

Advanced devices like Cisco 2518 combines ethernet hub and router capabilities with a built-

in Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI). Although this can

be counted as one of the hybrid devices, it is commercially available as a hub.

Working

The most common operation it performs is that it repeats all the information it receives and

forward it to all PC terminals attached to it. This repetition of data results in unnecessary data

traffic being sent to the network. Therefore the data is sent in bulk without the identificationof its destination.

Types

Passive hubs, active hubs and intelligent hubs are three kinds of hubs most frequently used.

Hubs are not often preferably used because they are considered passive devices, which do not

respond to the electrical signals. Such hubs which are not capable of regenerating electrical

signals to efficiently transfer data packets are known as Passive hubs. Passive hubs are often

termed as concentrators. More recently there are hubs available in the market which can

perform actively. Multi port repeaters which can amplify the electric signals to deliver packetof data are known as active hubs. When active hubs are developed more to be used by

companies they are known as intelligent hubs. The purpose of these hubs is to preserve the

space in an operation room or office. Various hubs are set one over the other to allow enough

space for the human working. Intelligent hubs can also back up media and multiple protocols.


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Repeater

The Repeater is a layer-1 internetworking device that

simply re-times and regenerates the frames to transfer data

from one network to another. Since the Ethernet repeater

operates at the physical layer, it does not understand frame

structures and can therefore only be used to connect

networks of the same type. For example, a repeater could

be used to link two Ethernet segments.

The ports can be AUI (Thick), BNC (Thin), RJ-45

(10 Base-T), or fiber optic (10 Base-FL)

Working

The basic function of a repeater is to take the data recieved on any port and immediatelyforward it to all other ports. In the process of forwarding the data, it is also retimed and

amplified to eliminate any distortion which may have been introduced after the signal was

originally transmitted.

The repeaters would amplify the data signals before sending them on to the uplinked

segment, thereby countering signal decay that occurs over extended lengths of wire. A WiFi

network repeater will pick up the signal from a wireless router and amplify it, propagating

signal strength to boost distance and coverage of the WLAN. For example, assume an

upstairs office gets only a weak signal from a router located in the basement. The building

might have a steel infrastructure, cordless phones and other forms of interference. One optionis to relocate the router on another floor to see if the entire building can be covered, but this

isnt always convenient.

Repeaters also provide a function called partitioning. If a repeater detects many collisions

originating on one of its ports, it assumes that a fault has occured somewhere on that segment

and isolates it from the rest of the network.

In general sense, repeaters can be categorized as under :

o An analog device that amplifies an input signal regardless of its nature.o A digital device that amplifies, reshapes and retimes these functions on a digital signal

Ethernet repeaters and extenders are digital devices.

Features

Digital Sampling and Amplification

Most of networking devices perform as repeaters by themselves. Repetition can be performed

by regular hubs and routers.

Devices like D-Link DIR-505 perform repetition of wireless communication signals.

Repeater

Purpose:Extending the limitsof an Ethernet networkbeyond the capacities of itscablesActing Layer : 1Commercial Examples :

Siecor RL6000


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Switch

A networking switch is the central device in a wired or

wireless LAN (local area network). It receives signals

from each computer on the network via Ethernet cables in

a wired network or radio waves in a wireless LAN. In

both cases, the networking switch directs traffic across the

LAN, enabling the computers to talk to each other and

share resources.

Most business networks today use switches to

connect computers, printers and servers within a

building or campus. A switch serves as a controller,

enabling networked devices to talk to each other

efficiently. Through information sharing and resource

allocation, switches save businesses money and

increase employee productivity.

Working

An Ethernet switch operates at the data link layer of the OSI model to create a separate

collision domain for each switch port. With 4 computers (e.g., A, B, C, and D) on 4 switch

ports, any pair (e.g. A and B) can transfer data back and forth while the other pair (e.g. C and

D) also do so simultaneously, and the two conversations will not interfere with one another.

Switches can be :

1. Unmanaged SwitchesAn unmanaged switch works right out of the box. It's not designed to be configured, so you

don't have to worry about installing or setting it up correctly. Unmanaged switches have less

network capacity than managed switches.

2. Managed SwitchesA managed network switch is configurable, offering greater flexibility and capacity than an

unmanaged switch. You can monitor and adjust a managed switch locally or remotely, to give

you greater network control.

Switch

Purpose: Redirecting trafficto a particular node/port inthe established networkActing Layer : 2(commercially available in other OSIlevel variants too)

Commercial Examples : D-Link DES-1210 Cisco Catalyst 6500


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Features :

Turn particular port range on or off and setting their priority

Link bandwidth and duplex settings

MAC filtering and other types of "port security" features which prevent MAC flooding

Use of Spanning Tree Protocol

SNMP monitoring of device and link health

Advanced FeaturesAdvanced switching platforms for moderate and high density 1G/10G distribution

deployments

Integrated services modules enhance security, manageability, and wireless control

Modern Cisco switches use Catalyst technology that uses CatOS operating system that

allows software level configuration of the switches. Some newer Catalyst switch models also

allow configuration via web-based graphical interface module which is hosted on a HTTP

server located on the switch.


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Bridge

A network bridge connects multiple network segments at

the data link layer. Bridges broadcast to all ports except

the port on which the broadcast was received. Bridges use

MAC addresses to learn which port is the data to be

forwarded to. Once the bridge associates a port and an

address, it will send traffic for that address to that port

only.

Bridges learn the association of ports and addresses by

examining the source address of frames that it sees on

various ports. Once a frame arrives through a port, its

source address is stored and the bridge assumes that MAC

address is associated with that port. The first time that a

previously unknown destination address is seen, the bridge will forward the frame to all ports otherthan the one on which the frame arrived.

Traditional bridges, though, support one network boundary, whereas switches usually offer

four or more hardware ports. Switches are sometimes called "multi-port bridges" for this

reason.

Working

In order to cut down on the collision rate, a single network can be subdivided into two or

more LANs. For example, a single LAN can be subdivided into several departmental LANs.

Most of the traffic in each departmental network stays within the department network, and so

it needn't travel through all the workstations on all the LANs on the network. In this way,

collisions are reduced. Bridges are used to link the networks. The only traffic that needs to

travel across bridges is traffic bound for another network. Any traffic within the LAN need

not travel across a bridge.

Bridges consult a learning table that has the addresses of all the network nodes in it. If a

bridge finds that a packet belongs on its own LAN, it keeps the packet inside the LAN. If it

finds that the workstation is on another LAN, it forwards the packet. The bridge constantly

updates the learning table as it monitors and routes traffic.

Bridge v/s Switch

Switches and Bridges are pretty similar, both operate at the Data Link layer (just above

Physical) and both can filter data so that only the appropriate segment or host receives a

transmission. Both filter packets based on the physical address of the sender/receiver

although newer switches sometimes include the capabilities of a router and can forward data

based on IP address (operating at the Network Layer) and are referred to as IP Switches.

Often the desired results could be achieved using either a switch or a bridge but bridges are

used to as an interface between two networks while minimizing overall traffic.

Bridge

Purpose: Filter and Forwarddata between networkboundariesActing Layer : 2Commercial Examples : D-Link Xtreme Duo Cisco Aironet 1400 Wi


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Router

A router is a device that forwards data packets along

networks through the best possible route. Router reads the

IP header of the packet and using this information in its

routing table or routing policy, it directs the packet to the

next network on its journey. Routers perform the traffic

directing functions on the Internet. A data packet is

typically forwarded from one router to another through

the networks that constitute the internetwork until it gets

to its destination node.

When data is sent between locations on one network or

from one network to a second network the data is always

seen and directed to the correct location by the router. The router accomplishes this by using headers

and forwarding tables to determine the best path for forwarding the data packets, and they also useprotocols such as ICMP to communicate with each other and configure the best route between any

two hosts.

Working

A router has interfaces for different physical types of network connections, (such as copper

cables, fiber optic, or wireless transmission). It also contains firmware for different

networking protocol standards. Each network interface uses this specialized computer

software to enable data packets to be forwarded from one protocol transmission system to

another. The routers exchange information about destination addresses, using a dynamicrouting protocol. Each router builds up a table listing the preferred routes between any two

systems on the interconnected networks.

Routers may also be used to connect two or more logical groups of computer devices known

as subnets, each with a different sub-network address. The subnets addresses recorded in the

router do not necessarily map directly to the physical interface connections.A router has two

stages of operation called planes:

1. Control plane: A router records a routing table listing what route should be used toforward a data packet, and through which physical interface connection. It does this using

internal pre-configured addresses, called static routes.

2. Forwarding plane: The router forwards data packets between incoming and outgoinginterface connections. It routes it to the correct network type using information that the

packet header contains. It uses data recorded in the routing table control plane.

Routers can be :

Access routers

They are simple low cost office/home models. They do not need hierarchical routing of their

own. Some of them are capable of running alternative free Linux-based firmwares.

Router

Purpose: Forward networkdata through the networkActing Layer : 3Commercial Examples :

Cisco XR 12000 Series Cisco 800 Series

(for home use)


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Eg. Cisco 800, Cisco1900 Series

Distribution

Distribution routers aggregate traffic from multiple access routers, either at the same site, or

to collect the data streams from multiple sites to a major enterprise location. Distribution

routers are often responsible for enforcing quality of service across a WAN, so they may haveconsiderable memory installed, multiple WAN interface connections, and substantial onboard

data processing routines. They may also provide connectivity to groups of file servers or

other external networks.

Eg. Cisco 7600 Series

Core

They are high bandwidth routers which provide a collapsed backbone interconnecting the

distribution tier routers from multiple buildings of a campus, or large enterprise locations.

Eg. Cisco Carrier Routing System which provides network flow upto 322 Tbps

Advanced Features :

Layer 2 VPN and Layer 3 VPN services

Mobile aggregation

Video service-delivery networks

Some advanced models extend network as a platform for cloud computing

Most of modern routers come with built-in Wi-Fi capabilities


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Gateway

Gateway is a device on a network that serves as an

entrance to another network. In enterprises, the gateway is

the computer that routes the traffic from a workstation to

the outside network that is serving the Web pages. For

regular home users, Gateway is present at their ISP.

The gateway node also operates as a firewall and a proxy

server. A firewall is a system created to prevent

unauthorized admission into a private network. A proxy

server is located right between a client application such as

a web browser and the real server.

Working

On an IP network, clients send IP packets with a

destination outside a given subnet mask to a network

gateway. A subnet mask defines the IP range of a private network. For example, if a private

network has a base IP address of 192.168.0.0 and has a subnet mask of 255.255.255.0, then

any data going to an IP address outside of 192.168.0.X will be sent to that network's gateway.

While forwarding an IP packet to another network, the gateway might or might not perform

Network Address Translation.

A gateway is an essential feature of most routers, although other devices (such as any PC or

server) can function as a gateway. A gateway may contain devices such as protocoltranslators, impedance matching devices, rate converters, fault isolators, or signal translators

as necessary to provide system interoperability. It also requires the establishment of mutually

acceptable administrative procedures between both networks.

Features and Functions

1. A gateway can be implemented in software, hardware and some time as a mixture oftogether. There are lots of equipments and techniques which are being processed such as

voice and data communication.

2. The gateways are the best option to achieve the multimedia communications betweendissimilar networks because every network has different protocol and characteristics.

3. Gateway controls the processing information across the network which containsinformation about to set up the actual end to end call.

4. A network gateway work like a firewall and filters packets. It also separates corporatenetwork as intranet from a public network.

5. A gateway may also install on a stand alone device. A gateway performs as theinterface between local and wide area protocols such as TCP/IP on the Internet.

GatewayPurpose: Provide access to anetworkActing Layer : 4-7Commercial Examples :

Microsoft CE 5.0provides very powerfulfeatures for Gateway

Operation :A configured network node

acts as the Gateway


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Default Gateway and Internet Access

Default gateway is the device that passes traffic from the local subnet to devices on other

subnets. The default gateway often connects a local network to the Internet, although internalgateways for local networks also exist.

Default gateways are important to make IP routing work efficiently. In most cases, the router

that acts as the default gateway for TCP/IP hosts--either a dedicated router or a computer that

connects two or more network segments--maintains knowledge of other networks in the

larger network and how to reach them.

TCP/IP hosts rely on default gateways for most of their communication needs with hosts on

remote network segments. In this way, individual hosts are freed of the burden of having to

maintain extensive and continuously updated knowledge about individual remote IP networksegments. Only the router that acts as the default gateway needs to maintain this level of

routing knowledge to reach other remote network segments in the larger internetwork.


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Brouter

A network device that combines the functions of a bridge

and a router in one unit. It may support multiple protocolsby routing routable packets and bridging non-routable

packets. Or, it may support a variety of bridging

requirements while providing routing.

Working

Brouters operate at both the network layer for

routable protocols and at the data link layer for non-

routable protocols. As networks continue to become

more complex, a mix of routable and non-routableprotocols has led to the need for the combined

features of bridges and routers.

Brouters handle both routable and non-routable features by acting as routers for routable

protocols and bridges for non-routable protocols. Bridged protocols might propagate

throughout the network, but techniques such as filtering and learning might be used to reduce

potential congestion. Brouters are used as connecting devices in the networking system, so it

acts as a bridge in a network and as a router in an internetwork.

A Brouter transmits two types of traffic at the exact same time: bridged traffic and routed

traffic. For bridged traffic, the Brouter handles the traffic the same way a bridge or switch

would, forwarding data based on the physical address of the packet. This makes the bridged

traffic fairly fast, but slower than if it were sent directly through a bridge because the Brouterhas to determine whether the data packet should be bridged or routed.

Brouter

Purpose: Provide features ofbridge and routerActing Layer : 2, 3Commercial Examples : 2wire 2700HG-B Router

(Legacy Device)

*2Wire is now merged with Pace


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Multilayer Switch

A multilayer switch (MLS) is a computer networking

device that switches on some other layers along with OSIlayer 2. Multi-Layer Switching (MLS) has become a

highly desired method of accelerating routing performance

through the use of dedicated Application Specific

Integrated Circuits (ASICs). Traditional routing is done

through a central CPU and software. MLS offloads a

significant portion of routing (packet rewrite) to hardware,

and thus has also been termed switching. MLS and Layer

3 switching are equivalent terms.

Working

MultiLayer Switching (MLS) is Ethernet-based

routing switch technology by Cisco that provides Layer 3 (L3) switching in conjunction with

existing routers.The major difference between the packet switching operation of a router and

that of a Layer 3 switch is the physical implementation. In general-purpose routers, packet

switching takes place using software that runs on a microprocessor, whereas a Layer 3 switch

performs this using dedicated application-specific integrated circuit (ASIC) hardware

A Multilayer Switch (MLS) can prioritize packets by the 6 bits in IP DSCP (differentiated

services CodePoint).

Some switches can use up to OSI layer 7 packet information; these may be called layer 4-7

switches, content-switches, content services switches, web-switches or application-switches.

Content switches are typically used for load balancing among groups of servers. Load

balancing can be performed on HTTP, HTTPS, VPN, or any TCP/IP traffic using a specific

port. Load balancing is explained later in this whitepaper.

Multilayer Switch

Purpose: Provide services forfurther layersActing Layer : 2, 3 (IP MLS),4-7 (Content Switch) Commercial Examples :

CISCO Catalyst6500/6000 provide

support for MLS


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Network Interface Card

A network interface card/ controller, also called network

adapter is a computer hardware component that connects a

computer to a computer network. It implements the

electronic circuitry required to communicate using a

specific physical layer and data link layer standard such as

Ethernet, Wi-Fi, or Token Ring. This provides a base for a

full network protocol stack, allowing communication

among small groups of computers on the same LAN and

large-scale network communications through routable

protocols, such as IP.

Working

Early network interface controllers were commonlyimplemented on expansion cards that plugged into a

computer bus.

The NIC may use one or more of four techniques to transfer data:

Polling is where the CPU examines the status of the peripheral under program control.

Programmed I/O is where the microprocessor alerts the designated peripheral by applying

its address to the system's address bus.

Interrupt-driven I/O is where the peripheral alerts the microprocessor that it is ready totransfer data.

Direct memory access is where an intelligent peripheral assumes control of the system bus

to access memory directly. This removes load from the CPU but requires a separate processor

on the card.

A wireless network interface controller (WNIC) is a network interface controller which

connects to a radio-based computer network rather than a wire-based network such as Token

Ring or Ethernet. A WNIC, just like other NICs, works on the Layer 1 and Layer 2 of the OSI

Model. A WNIC is an essential component for wireless desktop computer. This card uses anantenna to communicate through microwaves.

Network InterfaceCard

Purpose: Connects acomputer/node to a networkActing Layer : 1 Commercial Examples :

Realtek RTL8100 Family Broadcom 802.11g

Adapter (Wireless)


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Modem

A modem (a modulator/demodulator) is a device that

lets a computer connect to a network through phone

lines or other standard media. It performs the task of

modulation and demodulation of digital signals in the

computer and analog signals in the phone line.

Working

Modems are commercially available as internal modems

which are plugged in the motherboard and external

modems, which can be connected externally through a

serial connection.

A standard modem of today contains two functional parts: an analog section for generating

the signals and operating the phone, and a digital section for setup and control. The modem

can be in one of two modes, data mode in which data is sent to and from the computer over

the phone lines, and command mode in which the modem listens to the data from the

computer for commands, and carries them out. A typical session consists of powering up the

modem (often inside the computer itself) which automatically assumes command mode, then

sending it the command for dialing a number. After the connection is established to the

remote modem, the modem automatically goes into data mode, and the user can send and

receive data. When the user is finished, the escape sequence, "+++" followed by a pause of

about a second, may be sent to the modem to return it to command mode, then a command

(e.g. "ATH") to hang up the phone is sent. Note that on many modem controllers it is possible

to issue commands to disable the escape sequence so that it is not possible for data being

exchanged to trigger the mode change inadvertently.

Variants

ADSL modems, a more recent development, are not limited to the telephone's voiceband

audio frequencies.

DSL modems utilize a property that standard twisted-pair telephone cable can be used for

short distances to carry much higher frequency signals than what the cable is actually rated tohandle. This is also why DSL modems have a distance limitation.

Cable modems use a range of frequencies originally intended to carry RF television channels,

and can coexist on the same single cable alongside standard RF channel signals. Multiple

cable modems attached to a single cable can use the same frequency band, using a low-level

media access protocol to allow them to work together within the same channel. Typically, 'up'

and 'down' signals are kept separate using frequency division multiple access.

ModemPurpose: Performs Modulationand Demodulation betweenanalog and digital signalsActing Layer : 1Commercial Examples : D-Link standard 56kbps D-Link DSL-2740BR


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Firewall

A firewall, working closely with a router program,

examines each network packet to determine whether

to forward it toward its destination. A firewall also

includes or works with a proxy server that makes

network requests on behalf of workstation users. A

firewall is often installed in a specially designated

computer separate from the rest of the network so that

no incoming request can get directly at private

network resources.

There are a number of firewall screening methods. A simple one is to screen requests to make

sure they come from acceptable (previously identified) domain name and Internet Protocol

addresses. For mobile users, firewalls allow remote access in to the private network by theuse of secure logon procedures and authentication certificates.

Types

Packet filters

Network layer firewalls, also called packet filters, operate at a relatively low level of the

TCP/IP protocol stack, not allowing packets to pass through the firewall unless they match

the established rule set. The firewall administrator may define the rules; or default rules may

apply. The term "packet filter" originated in the context of BSD operating systems.

Modern firewalls can filter traffic based on many packet attributes like source IP address,

source port, destination IP address or port, destination service like WWW or FTP. They can

filter based on protocols, TTL values, netblock of originator, of the source, and many other

attributes.

Application-layer Firewalls

Application-layer firewalls work on the application level of the TCP/IP stack, and may

intercept all packets traveling to or from an application. On inspecting all packets for

improper content, firewalls can restrict or prevent outright the spread of networked computerworms and trojans. The additional inspection criteria can add extra latency to the forwarding

of packets to their destination.

Proxies

A proxy server may act as a firewall by responding to input packets in the manner of an

application, while blocking other packets. A proxy server is a gateway from one network to

another for a specific network application, in the sense that it functions as a proxy on behalf

of the network user.

FirewallPurpose: Protect a node or anetwork by acting as anintermediate agent between thecommunicating entities.


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Load Balancer

A load balancer is a device that acts as a reverse

proxy and distributes network or application traffic

across a number of servers. Load balancers are used to

increase capacity (concurrent users) and reliability of

applications. They improve the overall performance of

applications by decreasing the burden on servers

associated with managing and maintaining application

and network sessions, as well as by performing application-specific tasks.

It is used to distribute workload across multiple computers or a computer cluster, network

links, central processing units, disk drives, or other resources, to achieve optimal resourceutilization, maximize throughput, minimize response time, and avoid overload. Using

multiple components with load balancing, instead of a single component, may increase

reliability through redundancy. The load balancing service is usually provided by dedicated

software or hardware, such as a multilayer switch or a Domain Name System server.

Load Balancers offer following features :

Asymmetric load: A ratio can be manually assigned to cause some backend servers to get a

greater share of the workload than others.

Priority activation: When the number of available servers drops below a certain number, or

load gets too high, standby servers can be brought online

Distributed Denial of Service (DDoS) attack protection: load balancers can provide features

such as SYN cookies and delayed-binding (the back-end servers don't see the client until it

finishes its TCP handshake) to mitigate SYN flood attacks and generally offload work from

the servers to a more efficient platform.

TCP buffering: the load balancer can buffer responses from the server and spoon-feed the

data out to slow clients, allowing the web server to free a thread for other tasks faster than it

would if it had to send the entire request to the client directly.

Health checking: the balancer will poll servers for application layer health and remove failed

servers from the pool.

Priority queuing: also known as rate shaping, the ability to give different priority to different

traffic.

Firewall: direct connections to backend servers are prevented, for network security reasons

Firewall is a set of rules that decide whether the traffic may pass through an interface or not.

Load Balancer

Purpose: Forwards clientrequests to the server while

performing some additionalaction
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Proxy Server

A proxy server is a server that acts as an intermediary

for requests from clients seeking resources from other

servers. A client connects to the proxy server, requesting

some service, such as a file, connection, web page, or

other resource available from a different server. The

proxy server evaluates the request as a way to simplify

and control their complexity.

A proxy server receives a request for an Internet

service (such as a Web page request) from a user. If

it passes filtering requirements, the proxy server, assuming it is also a cache server , looks in

its local cache of previously downloaded Web pages. If it finds the page, it returns it to the

user without needing to forward the request to the Internet. If the page is not in the cache, the

proxy server, acting as a client on behalf of the user, uses one of its own IP addresses to

request the page from the server out on the Internet. When the page is returned, the proxy

server relates it to the original request and forwards it on to the user.

To the user, the proxy server is invisible; all Internet requests and returned responses appear

to be directly with the addressed Internet server. (The proxy is not quite invisible; its IP

address has to be specified as a configuration option to the browser or other protocol

program.)

The functions of proxy, firewall, and caching can be in separate server programs or combined

in a single package. A proxy server may in the same machine with a firewall server or it may

be on a separate server and forward requests through the firewall.

Protocol Converter

A Protocol Converter is a device used to convert

standard or proprietary protocol of one device to the

protocol suitable for the other device or tools to

achieve the interoperability. Protocols are software

installed on the routers which convert the data

formats, data rate and protocols of one network into

the protocols of the network in which data is

navigating. There are varieties of protocols used in

different fields like Power Generation, Transmission

& Distribution, Oil & Gas, Automaton, Utilities,

AMR, and Remote Monitoring applications. The

major protocol translation messages involve

conversion of data messages, events, commands and

time synchronization.

Protocol Converter

Purpose: Translationbetween two differentprotocolsActing Layer : 1-7 (dependson the protocols)Commercial Examples :

Aftec India APC SeriesWestermo MD-54(out of production)

Proxy ServerPurpose: Forwards clientrequests to the server while

performing some additionalaction

Networking Devices - Introductory Summary

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