chandan singh seminar report pdf.......router

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ACKNOWLEDGEMENT

I wish to extend my sincere gratitude to my seminar guide, Ms. Sonam Singh

Lecturer, Department of Electronics & Communication, for her valuable

guidance and encouragement which has been absolutely helpful in successful

completion of this seminar.

I am indebted to Prof. Poonam Pathak, Professor and Head, Department of

Electronics & Communication for her valuable support.

I am also grateful to my parents and friends for their timely aid without which I

wouldn’t have finished my seminar successfully. I extend my thanks to all my

well-wishers and all those who have contributed directly and indirectly for the

completion of this work.

And last but not the least; I thank God Almighty for his blessings without which

the completion of this seminar would not have been Possible

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ABSTRACT

This seminar discusses the basic concepts of Router.Basically A router is a

device that forwards data packets between computer networks, creating an

overlay internetwork. A router is connected to at least two networks,

commonly two LANs or WANs or a LAN and its ISP's network. Routers are

located at gateways, the places where two or more networks connect.

Various types of Router such as Broadband router,Wireless router,Core router

etc are also discussed in this report.Alongwith this it also includes the

components of router such as motherboard,CPU,Memory etc.It also describes

its various functions,advantages & disadvantages.

Besides this basic concepts of hubs,switches,delivering,forwarding & routing

are also discussed

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INDEX

1. Acknowledgement 01

2. Abstract 02

3. Index 03

4. Introduction 05

5. Router 06

6. Symbol Of Router 07

7. Difference between Hubs ,Switches & Router 09

8.Delivery,Forwarding & Routing 13

8.1 Delivery

8.2 Forwarding

8.3 Routing

9.Router and the network layer 16

10.Types of Router 18

10.1 Broadband Router

10.2 Wireless Router

10.3 Edge Router

10.4 Core Router

11. Functions of Router 23

11.1 Restrict Broadcasts to the LAN

11.2 Act as the Default Gateway

11.3 Move (route) Data between Networks

11.4 Learn and Advertise Loop-Free Paths

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12. Router Component 26

12.1 Router Motherboard

12.2 Router CPU

12.3 RAM

12.4 NVRAM

12.5 Flash Memory

12.6 ROM

13. Applications of Router 29

13.1 Access

13.2 Distribution

13.3 Security

13.4 Core

14. Advantages of Router 33

15. Disadvantages of Router 34

16. Conclusion 35

17. Bibiliography 36

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INTRODUCTION

Firstly we understand the concept of what is broadband connection in

communication networks. Broadband is a high-capacity high-speed Data

transmission medium. This can be done on a single cable by establishing

different bandwidth channels. Broadband technology can be used to transmit

voice, data and video over long distances simultaneously.

Routers capture the information that come though broadband connection via a

modemvand deliver it to your computer. The router choose route for the

packet so that you receive the information firstly. Routers and multiport

devices and more sophisticated as compared to repeaters and brigdes.

Router s also support filtering and encapsulation like bridges. They operate at

physical data link and network layer of OSI model. Like bridges they are self

learning. As they can communicate their existence to other devices and can

learn of the existence of new routers. Nodes and LAN segments.

A router has access to the network layer address or logical address (IP

address) it contains a routing table that enables it to make decisions about the

route i.e. to determine which of several possible paths between the source

and destination is the best for a particular transmission. These routing tables

are dynamic are updated using routing protocols.

The router receive the packets from one connected network and pass them to

asecond connected network. However if a received packet contains the

address of a node that is on sone other network (of which the router is not a

member). The router determines which of its connected networks is the best

next relay point for that packet. Once the router has identified the best rout for

a packet to travel. It passes the packet along the appropriate network to

another router.

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ROUTER

A router is a device that forwards data packets between computer networks,

creating an overlay internetwork. A router is connected to at least two

networks, commonly two LANs or WANs or a LAN and its ISP's network.

Routers are located at gateways, the places where two or more networks

connect.

Routers use headers and forwarding tables to determine the best path for

forwarding the packets, and they use protocols such as ICMP to communicate

with each other and configure the best route between any two hosts.

When a data packet comes in one of the lines, the router reads the address

information in the packet to determine its ultimate destination. Then, using

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 reaches its

destination node

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The most familiar type of routers are

pass data, such as web pages, email, IM, and videos between the home

computers and the Internet. An example of a router would be the

owner's cable or DSL modem

More sophisticated routers, such as enterprise routers, connect large

business or ISP networks up to the powerful

high speed along the

routers are typically dedicated hardware devices, use of software

routers has grown increasingly common.

SYMBOL OF ROUTER

The most familiar type of routers are home and small office routers



DSL modem, which connects to the Internet through an


business or ISP networks up to the powerful core routers that forw

optical fiber lines of the Internet backbone

e typically dedicated hardware devices, use of software

routers has grown increasingly common.

SYMBOL OF ROUTER

home and small office routers that simply



, which connects to the Internet through an ISP.


that forward data at

Internet backbone. Though

e typically dedicated hardware devices, use of software-based

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DIFFERENCE BETWEEN HUB, SWITCH & ROUTER

The functions of the three devices are all quite different from one another,

even if at times they are all integrated into a single device. Which one do you

use when? Let's take a look... HUB

A common connection point for devices in a network. Hubs are commonly

used to connect segments of a LAN. A hub contains multiple ports. When

a packet arrives at one port, it is copied to the other ports so that all segments

of the LAN can see all packets.

SWITCH

In networks, a device that filters and forwards packets between LAN

segments. Switches operate at the data link layer (layer 2) and sometimes

the network layer (layer 3) of the OSI Reference Model and

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therefore support any packet protocol. LANs that use switches to

join segments are called switched LANs or, in the case of

switched Ethernet LANs.

ROUTER

A device that forwards data

at least two networks, commonly two

its ISP.s network. Routers are located at

more networks connect. Routers use

determine the best path for forwarding the pa

use protocols such as ICMP

the best route between any two hosts.

Today most routers have become something of a Swiss Army knife,

combining the features and functionality of a router and switch/hub into a

single unit. So conversations regarding these d

especially to someone new to computer networking.

The functions of a router, hub and a switch are all quite different from one

another, even if at times they are all integrated into a single

with the hub and the switch since these

network

Each serves as a central connection for all of your network equipment and

handles a data type known as frames. Frames carry your data. When a frame

any packet protocol. LANs that use switches to

are called switched LANs or, in the case of Ethernet networks,

switched Ethernet LANs.

data packets along networks. A router is connected to

at least two networks, commonly two LANs or WANs or a LAN and

network. Routers are located at gateways, the places where two or

more networks connect. Routers use headers and forwarding tables to

determine the best path for forwarding the packets, and they

ICMP to communicate with each other and configure

the best route between any two hosts.

ers have become something of a Swiss Army knife,


single unit. So conversations regarding these devices can be a bit misleading

especially to someone new to computer networking.

functions of a router, hub and a switch are all quite different from one

another, even if at times they are all integrated into a single device

with the hub and the switch since these two devices have similar roles on the



any packet protocol. LANs that use switches to

Ethernet networks,

. A router is connected to

or a LAN and

, the places where two or

and forwarding tables to

ckets, and they

to communicate with each other and configure

ers have become something of a Swiss Army knife,


evices can be a bit misleading

functions of a router, hub and a switch are all quite different from one

device. Let's start

two devices have similar roles on the



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is received, it is amplified and then transmitted on to the port of the destination

PC. The big difference between these two devices is in the method in which

frames are being delivered.

In a hub, a frame is passed along or "broadcast" to every one of its ports. It

doesn't matter that the frame is only destined for one port. The hub has no

way of distinguishing which port a frame should be sent to. Passing it along to

every port ensures that it will reach its intended destination. This places a lot

of traffic on the network and can lead to poor network response times.

Additionally, a 10/100Mbps hub must share its bandwidth with each and every

one of its ports. So when only one PC is broadcasting, it will have access to

the maximum available bandwidth. If, however, multiple PCs are

broadcasting, then that bandwidth will need to be divided among all of those

systems, which will degrade performance.

A switch, however, keeps a record of the MAC addresses of all the devices

connected to it. With this information, a switch can identify which system is

sitting on which port. So when a frame is received, it knows exactly which port

to send it to, without significantly increasing network response times. And,

unlike a hub, a 10/100Mbps switch will allocate a full 10/100Mbps to each of

its ports. So regardless of the number of PCs transmitting, users will always

have access to the maximum amount of bandwidth. It's for these reasons why

a switch is considered to be a much better choice then a hub.

Routers are completely different devices. Where a hub or switch is concerned

with transmitting frames, a router's job, as its name implies, is to

route packets to other networks until that packet ultimately reaches its

destination. One of the key features of a packet is that it not only contains

data, but the destination address of where it's going.

A router is typically connected to at least two networks, commonly two Local

Area Networks (LANs) or Wide Area Networks (WAN) or a LAN and its ISP's

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network . for example, your PC or workgroup and EarthLink. Routers are

located at gateways, the places where two or more networks connect.

Today, a wide variety of services are integrated into most broadband routers.

A router will typically include a 4 - 8 port Ethernet switch (or hub) and a

Network Address Translator (NAT). In addition, they usually include a

Dynamic Host Configuration Protocol (DHCP) server, Domain Name Service

(DNS) proxy server and a hardware firewall to protect the LAN from malicious

intrusion from the Internet.

All routers have a WAN Port that connects to a DSL or cable modem for

broadband Internet service and the integrated switch allows users to easily

create a LAN. This allows all the PCs on the LAN to have access to the

Internet and Windows file and printer sharing services.

Routers might have a single WAN port and a single LAN port and are

designed to connect an existing LAN hub or switch to a WAN. Ethernet

switches and hubs can be connected to a router with multiple PC ports to

expand a LAN. Depending on the capabilities (kinds of available ports) of the

router and the switches or hubs, the connection between the router and

switches/hubs may require either straight-thru or crossover (null-modem)

cables. Some routers even have USB ports, and more commonly, wireless

access points built into them.

Some of the more high-end or business class routers will also incorporate a

serial port that can be connected to an external dial-up modem, which is

useful as a backup in the event that the primary broadband connection goes

down, as well as a built in LAN printer server and printer port.

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DELIVERY, FORWARDING & ROUTING

DELIVERY

The network layer supervises the handling of the packets by the underlying

physical networks. We define this handling as the delivery of a packet.

o Direct Datagram Deliveries: When datagrams are sent between two

devices on the same physical network, it is possible for datagrams to be

delivered directly from the source to the destination. Imagine that you want

to deliver a letter to a neighbor on your street. You probably wouldn't

bother mailing it through the post office; you'd just put the neighbor’s name

on the envelope and stick it right into his or her mailbox.

o Indirect Datagram Deliveries: When two devices are not on the same

physical network, the delivery of datagrams from one to the other

is indirect. Since the source device can't see the destination on its local

network, it must send the datagram through one or more intermediate

devices to deliver it. Indirect delivery is analogous to mailing a letter to a

friend in a different city. You don't deliver it yourself—you put it into the

postal system. The letter journeys through postal system, possibly taking

several intermediate steps, and ends up in your friend's neighborhood,

where a postal carrier puts it into his or her mailbox.

FORWARDING

o For pure Internet Protocol (IP) forwarding function, a router is designed to

minimize the state information associated with individual packets. The

main purpose of a router is to connect multiple networks and forward

packets destined either for its own networks or other networks. A router is

considered aLayer 3 device because its primary forwarding decision is

based on the information in the Layer 3 IP packet, specifically the

destination IP address. This process is known as routing. When each

router receives a packet, it searches its routing table to find the best match

between the destination IP address of the packet and one of the network

addresses in the routing table. Once a match is found, the packet is

encapsulated in the Layer 2 data link frame for that outgoing interface. A

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router does not look into the actual data contents that the packet carries,

but only at the layer 3 addresses to make a forwarding decision, plus

optionally other information in the header for hints on, for example, quality

of service (QoS).

o Forwarding decisions can involve decisions at layers other than layer 3. A

function that forwards based on layer 2 information is properly called

a bridge. This function is referred to as layer 2 bridging, as the addresses

it uses to forward the traffic are layer 2 addresses (e.g. MAC

addresses on Ethernet).

o Besides making decision as to which interface a packet is forwarded to,

which is handled primarily via the routing table, a router also has to

manage congestion, when packets arrive at a rate higher than the router

can process. Three policies commonly used in the Internet are tail

drop, random early detection (RED), and weighted random early

detection (WRED). Tail drop is the simplest and most easily implemented;

the router simply drops packets once the length of the queue exceeds the

size of the buffers in the router. RED probabilistically drops datagrams

early when the queue exceeds a pre-configured portion of the buffer, until

a pre-determined max, when it becomes tail drop. WRED requires a

weight on the average queue size to act upon when the traffic is about to

exceed the pre-configured size, so that short bursts will not trigger random

drops.

o Another function a router performs is to decide which packet should be

processed first when multiple queues exist.

ROUTING

Routing is the process of selecting best paths in a network. In the past, the

term routing was also used to mean forwarding network traffic among

networks. However this latter function is much better described as simply

forwarding. Routing is performed for many kinds of networks, including

the telephone network (circuit switching), electronic data networks (such as

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the Internet), andtransportation networks. This article is concerned primarily

with routing in electronic data networks using packet switching technology.

In packet switching networks, routing directs packet forwarding (the transit of

logically addressed network packets from their source toward their ultimate

destination) through intermediate nodes. Intermediate nodes are typically

network hardware devices such as routers, bridges, gateways, firewalls,

or switches. General-purpose computers can also forward packets and

perform routing, though they are not specialized hardware and may suffer

from limited performance. The routing process usually directs forwarding on

the basis of routing tables which maintain a record of the routes to various

network destinations. Thus, constructing routing tables, which are held in the

router's memory, is very important for efficient routing. Most routing algorithms

use only one network path at a time. Multipath routing techniques enable the

use of multiple alternative paths.

In case of overlapping/equal routes, the following elements are considered in

order to decide which routes get installed into the routing table (sorted by

priority):

• Prefix-Length: where longer subnet masks are preferred (independent of

whether it is within a routing protocol or over different routing protocol).

• Metric: where a lower metric/cost is preferred (only valid within one and

the same routing protocol).

• Administrative distance: where a lower distance is preferred (only valid

between different routing protocols)

Routing, in a more narrow sense of the term, is often contrasted

with bridging in its assumption that network addresses are structured and that

similar addresses imply proximity within the network. Structured addresses

allow a single routing table entry to represent the route to a group of devices.

In large networks, structured addressing (routing, in the narrow sense)

outperforms unstructured addressing (bridging).

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ROUTER AND THE NETWORK LAYER

The main purpose of a router is to connect multiple networks and forward


considered a Layer 3 device because its primary forwarding decision is based

on the information in the Layer 3 IP packet, specifically the destination IP

address. This process is k

When a router receives a packet, it examines its destination IP address. If the

destination IP address does not belong to any of the router's directly

connected networks, the router must forward this packet to another router. In

the figure, R1 examines the destination IP address of the packet. After

searching the routing table, R1 forwards the packet onto R2. When R2

receives the packet, it also examines the packet's destination IP address.

After searching its routing table, R2 forwards the

connected Ethernet network to PC2.

When each router receives a packet, it searches its routing table to find the

best match between the destination IP address of the packet and one of the

network addresses in the routing table. On

encapsulated in the layer 2 data link frame for that outgoing interface. The

type of data link encapsulation depends on the type of interf

Ethernet or HDLC.






s process is known as routing.




, R1 examines the destination IP address of the packet. After



After searching its routing table, R2 forwards the packet out its directly




network addresses in the routing table. Once a match is found, the packet is


type of data link encapsulation depends on the type of interf









, R1 examines the destination IP address of the packet. After



packet out its directly




ce a match is found, the packet is


type of data link encapsulation depends on the type of interface, such as

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Eventually the packet reaches a router that is part of a network that matches

the destination IP address of the packet. In this example, router R2 receives

the packet from R1. R2 forwards the packet out its Ethernet interface, which

belongs to the same network as the destination device, PC2.

This sequence of events is explained in more detail later in this chapter.

Routers Operate at Layers 1, 2, and 3

A router makes its primary forwarding decision at Layer 3, but as we saw

earlier, it participates in Layer 1 and Layer 2 processes as well. After a router

has examined the destination IP address of a packet and consulted its routing

table to make its forwarding decision, it can forward that packet out the

appropriate interface toward its destination. The router encapsulates the

Layer 3 IP packet into the data portion of a Layer 2 data link frame

appropriate for the exit interface. The type of frame can be an Ethernet,

HDLC, or some other Layer 2 encapsulation - whatever encapsulation is used

on that particular interface. The Layer 2 frame is encoded into the Layer 1

physical signals that are used to represent bits over the physical link.

To understand this process better, refer to the figure. Notice that PC1

operates at all seven layers, encapsulating the data and sending the frame

out as a stream of encoded bits to R1, its default gateway.

R1 receives the stream of encoded bits on its interface. The bits are decoded

and passed up to Layer 2, where R1 decapsulates the frame. The router

examines the destination address of the data link frame to determine if it

matches the receiving interface, including a broadcast or multicast address. If

there is a match with the data portion of the frame, the IP packet is passed up

to Layer 3, where R1 makes its routing decision. R1 then re-encapsulates the

packet into a new Layer 2 data link frame and forwards it out the outbound

interface as a stream of encoded bits.

R2 receives the stream of bits, and the process repeats itself. R2

decapsulates the frame and passes the data portion of the frame, the IP

packet, to Layer 3 where R2 makes its routing decision.

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TYPES OF ROUTER

BROADBAND ROUTER

A broadband router combines the features of a traditional network switch,

anetwork firewall, and a DHCP server. Broadband routers are designed for

convenience in setting up home networks, particularly for homes with high-

speed Internet service. Besides easier sharing of a home Internet connection,

broadband routers also enable sharing of files, printers and other resources

among home computers.

A broadband router utilizes the Ethernet standard for wired connections.

Traditional broadband routers required Ethernet cables be run between the

router, the broadband modem, and each computer on the home network.

Newer broadband routers also incorporate wireless networking capability

utilizing the Wi-Fistandards.

Several manufacturers offer broadband router products to consumers.

Features that differentiate broadband router products

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WIRELESS ROUTER

A wireless router is a device that performs the functions of a router but also

includes the functions of a wireless access point. It is commonly used to

provide access to the Internet[note 1] or a computer network. It does not require

a wired link, as the connection is made wirelessly, via radio waves. It can

function in a wired LAN (local area network), in a wireless-only LAN (WLAN),

or in a mixed wired/wireless network, depending on the manufacturer and

model.

Most current wireless routers have the following characteristics:

• One or multiple NICs supporting Fast Ethernet or Gigabit

Ethernet integrated into the main SoC

• One or multiple WNICs supporting a part of the IEEE 802.11-standard

family also integrated into the main SoC or as separate chips on

the Printed circuit board. It also can be a distinct card connected over

a MiniPCI or MiniPCIe interface.

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• So far the PHY-Chips for the WNICs are generally distinct chips on the

PCB. Dependent on the mode the WNIC supports, i.e. 1T1R, 2T2R or

3T3R, one WNIC have up to 3 PHY-Chips connected to it. Each PHY-Chip

is connected to a Hirose U.FL-connector on the PCB. A so-called pigtail

cable connects the Hirose U.FL either to a RF connector, in which case

the antenna can be changed or directly to the antenna, in which case it is

integrated into the casing. Common are single-band (i.e. only for 2.4 GHz

or only for 5 GHz) and dual-band (i.e. for 2.4 and 5 GHz) antennas.

• Often an Ethernet Switch supporting Gigabit Ethernet or Fast Ethernet,

with support for IEEE 802.1Q, integrated into the main SoC

(MediaTekSoCs) or as separate Chip on the PCB.

• Some wireless routers come with either xDSL

modem, DOCSIS modem, LTE modem, or fiber optic modem integrated.

• IEEE 802.11n compliant or ready.

• Some dual-band wireless routers operate the 2.4 GHz and 5 GHz bands

simultaneously.

• Some high end dual-band wireless routers have data transfer rates of at

most 300 Mbit/s (For 2.4 GHz band) and 450 Mbit/s (For 5 GHz band).

• Some wireless routers have 1 or 2 USB port(s). For wireless routers

having 1 USB port, it is designated for either printer or desktop/mobile

external hard disk drive. For wireless routers having 2 USB ports, one is

designated for the printer and the other one is designated for either

desktop or mobile external hard disk drive.

• Some wireless routers have a USB port specifically designed for

connecting 3G mobile broadband modem aside from connecting the

wireless router to a xDSL modem.

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EDGE ROUTER An edge router is a specialized router residing at the edge or boundary of a

network. This router ensures

networks, a wide area network or the Internet. An edge router uses an

External Border Gateway Protocol, which is used extensively over the Internet

to provide connectivity with remote networks.

Instead of providing communication with an internal network, which the core

router already manages, an edge router may provide communication with

different networks and autonomous systems.

This term is also sometimes known as an access router or core router.

Edge routers use External BGP Protocol for data transmission because they

are intermediary devices between two different networks and operate at the

external or border layer of the network. There are several types of edge

routers, including edge routers placed

an essential device for connecting the host network with the Internet.

Whenever a node sends data on a network unmonitored by the host

administrator, the data packet is sent to the last router on the authorized

network, which is the edge router.

CORE ROUTER

An edge router is a specialized router residing at the edge or boundary of a

network. This router ensures the connectivity of its network with external



ectivity with remote networks.

ding communication with an internal network, which the core




routers use External BGP Protocol for data transmission because they



routers, including edge routers placed at the outer boundary of the network as




rk, which is the edge router.

An edge router is a specialized router residing at the edge or boundary of a

the connectivity of its network with external



ding communication with an internal network, which the core




routers use External BGP Protocol for data transmission because they



at the outer boundary of the network as




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A core router is a router designed to operate in the Internet backbone, or core.

To fulfill this role, a router must be able to support multiple

telecommunications interfaces of the highest speed in use in the core Internet

and must be able to forward IP packets at full speed on all of them. It must

also support the routing protocols being used in the core. A core router is

distinct from an edge router: edge routers sit at the edge of a backbone

network and connect to core routers

.

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FUNCTION OF A ROUTER

A router (including a wireless router) is a specialized networking device

connected to two or more networks running software that allows the router to

move data from one network to another. Router functions in an Internet

protocol based network operate at the network layer (OSI Model's layer 3).

The primary function of a router is to connect networks together and keep

certain kinds of broadcast traffic under control they are several companies

that make routers cisco,Linksys , Juniper, Netgear, NORTEL, Redback,

Lucent

FUNCTIONS OF A ROUTER (identify and describe)

1. Restrict broadcasts to the LAN

2. Act as the default gateway.

3. Perform Protocol Translation (Wired Ethernet to Wireless/WiFi, or Ethernet

to CATV)

4. Move (route) data between networks

5. Learn and advertise loop free paths

Restrict Broadcasts to the LAN

Networks (especially Ethernet networks) use broadcast communication at

the physical, datalink and network layer. Network layer broadcasts are

transmissions sent to all hosts using the network layer protocol

(usually Internet Protocol [IP] or IPX). Network broadcast communication is

used to communicate certain kinds of information that makes

the network function (ARP, RARP, DHCP, IPX-SAP broadcasts etc.). Since

several devices could attempt to transmit simultaneously and cause collisions,

it is preferable to separate large sets of hosts into different broadcast domains

using a switch, or router.

As the number of hosts on the network increases, the amount

of broadcast traffic increases. If enough broadcast traffic is present on

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the network, then ordinary communication across the network becomes

difficult.

To reduce broadcasts, a network administrator can break up a network with a

large number of hosts into two smaller networks. Broadcasts are then

restricted to each network, and the router performs as the 'default gateway' to

reach the hosts on the other networks.

Act as the Default Gateway

Especially in today's networks, people want to use their computer to connect

to the Internet. When your computer wants to talk to a computer on

another network, it does so by sending your data to the default gateway. The

default gateway is the local router connected to the same network your

computer is connected to. The router serving as the default gateway receives

your data, looks for the remote address of that far-off computer and makes a

routing decision. Based on that routing decision, it forwards your data out a

different interface that is closer to that remote computer. There could be

several routers between you and the remote computer, so several routers will

take part in handing off the packet, much like a fireman's bucket brigade.

Move (route) Data between Networks

Routers have the capability to move data from one network to another. This

allows two networks managed by different organizations to exchange data.

They create a network between them and exchange data between the routers

on that network. Because a router can accept traffic from any kind of network

it is attached to, and forward it to any other network, it can also allow networks

that could not normally communicate with each other to exchange data. In

technical terms, a token ring network and an ethernet network can

communicate over a serial network. Routers make all this possible.

A router can take in an Ethernet frame, strip the ethernet data off, and then

drop the IP data into a frame of another type such as SDH/SONET, PDH/T1,

ATM, FDDI. In this way a router can also perform 'protocol conversion',

provided it has the appropriate hardware and software to support such a

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function. The whole point, however, is to forward the data from the interface it

receives data on, to another interface that retransmits the received data onto

another interface serving another network.

Learn and Advertise Loop-Free Paths

Routers can only learn and advertise routes dynamically if they are using a

routing protocol such as RIP, OSPF, EIGRP, IS-IS or BGP. Otherwise, a

human has to configure the routes by hand, which is called static routing.

Routing moves data on a hop-by-hop basis, what is often called 'hot potato'

routing. If a set of routers ends up passing the data around in a circle, without

reaching the destination, it's calleda a 'routing loop'. Packets get handed off

around the loop until they die of old age: their 'Time To Live' expires. Time To

Live is a counter that is part of the IP datagram header. The Time To Live

value is decremented as it passes through each router and eventually it

reaches zero and is discarded.

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ROUTER COMPONENT

The components of a modern router differ very slightly from the PC

architecture. The most obvious difference internally is that there is no hard

disk. The router has non-volatile Flash memory to hold the operating system

whilst power is off. It also has another type of non-volatile memory known as

NVRAM to hold files containing the setup details for the router once it has

been configured. In common with the PC, the router has RAM and ROM, a

motherboard and ports through which it can be accessed.

Externally, the router has no monitor nor keyboard attached during normal

operation. To access the router, it is necessary to use a PC and the

appropriate program to interface with the router. When a router is first

purchased, it is necessary to use a PC running a terminal emulator such as

hyperterminal to set up the initial configuration, however once the router is in

operation in a live network, it is possible to access the router either by

TELNET or by using a modem to make a direct connection via POTS.

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ROUTER MOTHERBOARD

ROUTER CPU

50 MHz CPUs are generally used for small offices & homes.For more

powerful purposes, processors from Motorola, Silicon Graphics, etc. are used.

RAM

It is also called dynamic RAM (DRAM), has the following characteristics and

functions:

1. Stores routing tables

2. Holds ARP cache

3. Holds fast-switching cache

4. Performs packet buffering (shared RAM)

5. Provides temporary memory for the configuration file of the router while

the router is powered on

6. Loses content when router is powered down or restarted

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NVRAM

It has the following characteristics and functions:

1. Provides storage for the startup configuration file

2. Retains content when router is powered down or restarted

Flash memory


1. Holds the operating system image (IOS)

2. Allows software to be updated without removing and replacing chips on

the processor

3. Retains content when router is powered down or restarted.

4. Can store multiple versions of IOS software

5. Is a type of electronically erasable, programmable ROM (EEPROM)

Read-only memory (ROM)


1. Maintains instructions for power-on self test (POST) diagnostics

2. Stores bootstrap program and basic operating system software

3. Requires replacing pluggable chips on the motherboard for software

upgrades

Interfaces have the following characteristics and functions:

• Connect router to network for frame entry and exit

• Can be on the motherboard or on a separate module

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APPLICATIONS OF ROUTER

When multiple routers are used in interconnected networks, the routers

exchange information about destination addresses using a dynamic routing

protocol. Each router builds up a table listing the preferred routes between

any two systems on the interconnected networks. 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 Communications protocol standards. Each network interface uses

this specialized computer software to enable data packets to be forwarded

from one protocol transmission system to another.

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.

• Control plane: A router records a routing table listing what route should be

used to forward a data packet, and through which physical interface

connection. It does this using internal pre-configured directives, called

static routes, or by learning routes using a dynamic routing protocol. Static

and dynamic routes are stored in the Routing Information Base (RIB). The

control-plane logic then strips the RIB from non essential directives and

builds a Forwarding Information Base (FIB) to be used by the forwarding-

plane.

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• Forwarding plane: The router forwards data packets between incoming

and outgoing interface 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 may provide connectivity within enterprises, between enterprises and

the Internet, and between internet service providers (ISPs) networks. The

largest routers (such as the Cisco CRS-1 or Juniper T1600) interconnect the

various ISPs, or may be used in large enterprise networks.[4] Smaller routers

usually provide connectivity for typical home and office networks. Other

networking solutions may be provided by a backbone Wireless Distribution

System (WDS), which avoids the costs of introducing networking cables into

buildings.

All sizes of routers may be found inside enterprises.[5] The most powerful

routers are usually found in ISPs, academic and research facilities. Large

businesses may also need more powerful routers to cope with ever increasing

demands of intranet data traffic. A three-layer model is in common use, not all

of which need be present in smaller networks.

ACCESS

Access routers, including 'small office/home office' (SOHO) models, are

located at customer sites such as branch offices that do not need hierarchical

routing of their own. Typically, they are optimized for low cost. Some SOHO

routers are capable of running alternative free Linux-based firmwares like

Tomato, OpenWrt or DD-WRT.

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 have considerable memory

installed, multiple WAN interface connections, and substantial onboard data

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

servers or other external networks.

SECURITY

External networks must be carefully considered as part of the overall security

strategy. Separate from the router may be a firewall or VPN handling device,

or the router may include these and other security functions. Many companies

produced security-oriented routers, including Cisco Systems' PIX and

ASA5500 series, Juniper's Netscreen, Watchguard's Firebox, Barracuda's

variety of mail-oriented devices, and many others.

CORE

In enterprises, a core router may provide a "collapsed backbone"

interconnecting the distribution tier routers from multiple buildings of a

campus, or large enterprise locations. They tend to be optimized for high

bandwidth, but lack some of the features of Edge Routers.[8]

INTERNET CONNECTIVITY AND INTERNAL USE

Routers intended for ISP and major enterprise connectivity usually exchange

routing information using the Border Gateway Protocol (BGP). RFC

4098 standard defines the types of BGP-protocol routers according to the

routers' functions:

• Edge router: Also called a Provider Edge router, is placed at the edge of

an ISP network. The router uses External BGP to EBGP protocol routers

in other ISPs, or a large enterpriseAutonomous System.

• Subscriber edge router: Also called a Customer Edge router, is located at

the edge of the subscriber's network, it also uses EBGP protocol to its

provider's Autonomous System. It is typically used in an (enterprise)

organization.

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• Inter-provider border router: Interconnecting ISPs, is a BGP-protocol

router that maintains BGP sessions with other BGP protocol routers in ISP

Autonomous Systems.

• Core router: A core router resides within an Autonomous System as a

back bone to carry traffic between edge routers.[10]

• Within an ISP: In the ISPs Autonomous System, a router uses internal

BGP protocol to communicate with other ISP edge routers,

other intranet core routers, or the ISPs intranet provider border routers.

• "Internet backbone:" The Internet no longer has a clearly identifiable

backbone, unlike its predecessor networks. See default-free zone (DFZ).

The major ISPs system routers make up what could be considered to be

the current Internet backbone core.[11] ISPs operate all four types of the

BGP-protocol routers described here. An ISP "core" router is used to

interconnect its edge and border routers. Core routers may also have

specialized functions in virtual private networks based on a combination of

BGP and Multi-Protocol Label Switching protocols.[12]

• Port forwarding: Routers are also used for port forwarding between private

internet connected servers.[5]

• Voice/Data/Fax/Video Processing Routers: Commonly referred to

as access servers or gateways, these devices are used to route and

process voice, data, video, and fax traffic on the internet. Since 2005,

most long-distance phone calls have been processed as IP traffic (VOIP)

through a voice gateway. Voice traffic that the traditional cable networks

uses. Use of access server type routers expanded with the advent of the

internet, first with dial-up access, and another resurgence with voice

phone service.

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ADVANTAGE OF ROUTER

In addition to packet forwarding, a router provides other services as well. To

meet the demands on today's networks, routers are also used :

1. To ensure steady, reliance availability of network connectivity. Routers use

alternative parts in the case the primary part fails to the delivery of

packets.

2. To provide integrated services of data, video, and voice over wired and

wireless networks.

For security, router helps in mitigating the impact of worms, viruses, and other

attacks on the network by permitting or denying the forwarding of packets.

Easily Shared Internet

One of the biggest reasons for using a router is to connect multiple users to

the Internet. Connecting to the Internet requires a publicly-unique IP address.

As such, Internet providers typically only offer a single IP address or charge

fees for large amounts of publicly routable addresses. The solution is to add a

router with network address translation enabled. Connecting to the Internet

through a router with NAT allows the router to use the single public IP address

and a series of UDP ports to share the connection. Without NAT, connecting a

large organization’s computers to the Internet becomes virtually impossible.

Security and Adaptability

Connecting an Internet modem directly to a PC exposes that PC to a host of

security issues. Furthermore, expanding a direct-connection network

becomes complicated without the addition of switches or a router and

communicating between the individual PCs becomes difficult. Using a router

as an intermediary between the “outside” network of the Internet and the

“inside” network of your organization provides a scalable environment that is

also, to a degree, easier to secure.

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DISADVANTAGE OF ROUTER

1. Router is more expensive than Hub, Bridge & Switch.

2. Router only waork with routable protocol.

3. Routing updates consume bandwidth.

4. Increase latency due to greater degree of packet filtering.

Complicated Setup

The aforementioned router requires NAT to be set up. In addition, each

computer must be assigned a private IP address that is typically organized by

a DHCP server. This is required for the simplest connections. Connecting to

additional IP-based networks adds additional complication in the form of

routing tables -- a table that describes the best route for reaching a desired

network. If IP telephony or video services are to be running on the IP network,

you’ll also need to consider quality of service configurations. QoS helps

prioritize one type of traffic, such as voice, over others when bandwidth is

limited. As additional services are added, more configuration becomes

required of the router.

Data Overhead

Unlike a point-to-point “layer 2” link, routers add additional IP-based headers.

These headers include information such as source and destination addresses,

UDP information and checksums. These headers are attached to every

payload of data. Large pieces of data are typically broken into thousands of

smaller headers, making this header data consume a percentage of the total

available bandwidth. Additionally, the routers communicate updates on the

network in order to maintain routing tables. When possible, eliminating the

routed network environment will offer a nominal speed gain.

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CONCLUSION

Thus a router is an electronic device that interconnects two or more computer

networks. It works at Layer 3, Network Layer in an intelligent manner and can

connect different network segments, whether they are in the same building or

even on the opposite side of the globe

It works in LAN, WAN environments and allows access to resources by

selecting the best path. It can interconnect different networks. A Router

changes packet size and format to match the requirements of the destination

network .

Routing is the process of selecting best paths in a network. In the past, the

term routing was also used to mean forwarding network traffic among

network. Routing is performed for many kinds of networks, including

the telephone network (circuit switching), electronic data networks (such as

the Internet), andtransportation networks

We have also studied about the various components of Router such as

motherboard,CPU,RAM ,NVRAM,ROM etc.Alongwith this certain applications

of router have also been studied

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BIBILIOGRAPHY

• The Router Book: A Complete Guide to the Router and Its

Accessories Paperback by Pat Warner (Author)

• Router Basics (Basics Series) Paperback by Patrick Spielman (Author)

• http://en.wikipedia.org/wiki/Router_(computing)

• http://ecomputernotes.com/computernetworkingnotes/communication-

networks/what-is-routers-explain-types-of-routers

• http://www.orbit-computer-solutions.com/Types-of-Router.php

• http://blogs.cisco.com/smallbusiness/understanding-the-different-types-of-

wireless-routers/

• http://compnetworking.about.com/od/homenetworking/a/routernetworks.ht

m

• https://www.google.co.in/search?q=what+is+router+motherboard&oq=wha

t+is+router&aqs=chrome.0.69i59j69i57j0l2j69i60l2.10055j0j8&sourceid=ch

rome&espv=210&es_sm=93&ie=UTF-8

• http://www.techpowerup.com/forums/threads/what-is-the-point-of-two-

ethernet-ports-on-my-motherboard.168960/

chandan singh seminar report pdf.......router

Engineering

broadband router

core router

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router cpu

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functions of router

disadvantages of router