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
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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
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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
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, 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
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.
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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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BBDNIIT Page 26
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.

ROUTER
BBDNIIT Page 27
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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BBDNIIT Page 28
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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BBDNIIT Page 29
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.

ROUTER
BBDNIIT Page 30
• 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

ROUTER
BBDNIIT Page 31
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.

ROUTER
BBDNIIT Page 32
• 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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BBDNIIT Page 33
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.

ROUTER
BBDNIIT Page 34
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.

ROUTER
BBDNIIT Page 35
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

ROUTER
BBDNIIT Page 36
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/

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