A router is a networking device that forwards data packets between computer networks. It chooses the best path within the network to send data from one PC to another. Routers use internal components like a CPU, RAM, and flash memory to run an operating system like Cisco IOS, which allows it to perform routing functions. Routers have external ports that connect to both local area networks and wide area networks. Routers can also act as firewalls by hiding private IP addresses and only exposing a public IP address to the internet, protecting devices on the private network.

1. Introduction To
ROUTER

2.  Farhan Noor Galib (09.01.04.015)
 Zahidul islam george
(09.01.04.023)

3. What is Router?
• A router is a device that acts as a
medium for interconnecting several
PCs. If a PC named compA wants to
send data to compB, the router will
choose the best path within the network
and send data.
• A router is a device that forwards data
packets between computer networks

4. Router is one kind of a Computer
A router is a computer, just like any other
computer including a PC. The very first
router, used for the Advanced Research
Projects Agency Network (ARPANET),
was the Interface Message Processor
(IMP). The IMP was a Honeywell 316
minicomputer; this computer brought the
ARPANET to life on August 30, 1969.
Interface Message Processor (IMP) – The First Internet Router

5. Router Classification
 Non Upgradeable  Upgradeable
 Cannot add and  Can add and remove
remove the Ethernet interfaces as per
or serial interfaces. requirement.
 Doesn’t have any  Number of slots
slot. available.

6. Some other Router types
Wireless router
It combines a number of base stations (wireless access point) as well as a number of wired LAN switch
It connects more than one computer to a single DSL line for Internet access. Modem Routers provides the network
Modem router address translation (NAT) which is required to support several computers
Brouter A Bridge Router or brouter is a network device that works as a bridge and as a router
This router interfaces with an ATM (Asynchronous Transfer Mode) network
Edge router
Access routers are used in 'small office/home office' (SOHO) networking models. Typically, they are optimized for low
Access router
cost
Distribution router Distribution routers aggregate traffic from multiple access routers. . They are often responsible for enforcing quality of
service across a WAN
A core router may provide a "collapsed backbone" interconnecting the distribution tier routers from multiple buildings
Core router of a campus, or large enterprise locations

7. Some other Router types…(Cont’d)
Wireless router Modem router Brouter Edge router
Access router Distribution router Core router

9. Forwarding Packets…(Cont’d)

10. Internal Components of a Router
CPU RAM ROM Flash NVRAM
NVRAM
Memory
CPU executes RAM is volatile ROM does not lose its This is volatile RAM,
Non an example
operating system memory and it loses its content when the Internetwork similar to Hard Disk.
text. Go ahead and
instructions, such as content when the router is powered Operating System replaceknown as
Also it with your
system initialization, router is restarted. It is down or restarted. A (IOS) developed by permanent storage and
own text
routing functions and also known as bootstrap program is Cisco is stored here. is used to load startup
switching functions. temporary storage and located here. It is same IOS is Command line configuration file.
is used to store running as the bios of the PC. interface.
configuration file.

11. Inside view of a router

12. External Ports (Interfaces) of Router
•WAN interfaces
1
•LAN interfaces - Ethernet
2
•Administration
3 interfaces(Configuration)
 Serial interface (S0, S1 etc) – 60 pin/26 pin(smart serial)
 ISDN interface(BRI0 etc) – RJ45
WAN  WAN interfaces are used to connect routers to external networks, usually
Interfaces over a larger geographical distance. Similar to LAN interfaces, each WAN
interface has its own IP address and subnet mask, which identifies it as a
member of a specific network.

13. Interfaces of router…(Cont’d)
 AUI (Attachment Unit Interface) (E0)15 pin
 10baseT – RJ45
LAN  As the name indicates, LAN interfaces are used to connect the router to the LAN, similar to how a PC Ethernet
Interfaces NIC is used to connect the PC to the Ethernet LAN. Like a PC Ethernet NIC, a router Ethernet interface also
has a Layer 2 MAC address and participates in the Ethernet LAN in the same way as any other hosts on that
LAN.
 Console – RJ45 – Local Administration
 Auxiliary – RJ45 – Remote Administration.
Administration  The console port is used to connect a terminal, or most often a PC running terminal emulator software, to
Interfaces configure the router without the need for network access to that router. The console port must be used during
initial configuration of the router.
 At times the auxiliary port can be used in ways similar to a console port. It can also be used to attach a modem.

14. Interfaces of router…(Cont’d)
Iterfaces along with their Ports

15. Router acting as Firewall
Why do we need firewall:
When our PC is directly connected to the internet, a globally unique IP address is
assigned to our PC by the Internet Service Provider (ISP), this address is public i.e. it
can be known to anyone anywhere on the internet. In such cases, anyone can use the
IP address of user machine to do some mischievous work.
How router act as firewall:
 What happens in such cases is,the IP address is assigned to the router by ISP
(Internet Service Provider) and not to the PC, now it’s the work of router to assign
private address to the PC.
 When we send any packet, router removes the source IP address and attaches its
own public IP address, in turn stores the information about all the changes which
were made.
 When any packet comes to the PC , router gets information which it has stored and
accordingly routes the packet to the source machine.
 In this way our PC is not visible on the net, but our PC can see the internet.

16. Router acting as Firewall…(Cont’d)
Lets take a
closer look

17. Router plane
A router has two stages of operation called planes:
 Control Plane
 Forwarding Plane
Control plane Forwarding plane
1 2
A router records a routing table listing what route The router forwards data packets between
should be used to forward a data packet, and incoming and outgoing interface connections. It
through which physical interface connection. It routes it to the correct network type using
does this using internal pre-configured addresses, information that the packet header contains. It uses
called static routes. data recorded in the routing table control plane.

18. Cisco IOS
A router cannot function without an operating system. Without an operating system, the hardware does not have any capabilities.
The Cisco Internetwork Operating System (Cisco IOS) is the system software in Cisco devices. Different company uses different
IOS for their devices i.e Juniper uses JUNOS for their devices.
The Cisco IOS provides devices with the following network services:
 Basic routing and switching functions
 Reliable and secure access to networked resources
 Network scalability
The services provided by the Cisco IOS are generally accessed using a command line interface (CLI). The IOS file itself is several
megabytes in size and is stored in flash. Flash memory provides non-volatile storage. This means that the contents of the memory
are not lost when the device loses power.

19. Accessing command line interface(CLI)
There are several ways to access the CLI environment. The most
usual methods are:
 Console
 Telnet or SSH
 AUX port
Console:
The CLI can be accessed through a console session, also known as
the CTY line. A console uses a low speed serial connection to
directly connect a computer or terminal to the console port
on the router or switch. The console port is accessible even if

20. Accessing CLI….(Cont’d)
Telnet and SSH:
• A method for remotely accessing a CLI
session is to telnet to the router. Unlike
the console connection, Telnet sessions
require active networking services on the
device.
• The Secure Shell (SSH) protocol is a more
secure method for remote device access.
This protocol provides the structure for a
remote login similar to Telnet, except that
it utilizes more secure network services.
SSH provides stronger password
authentication than Telnet and uses
encryption when transporting session data.
AUX port:
Another way to establish a CLI session
remotely is via a telephone dialup connection

21. Router configuration files
1 The startup configuration file 2 The running configuration file
1 The startup configuration file
 The startup configuration file (startup-config) is used
during system startup to configure the device.
 The startup configuration file is stored in non-volatile
RAM (NVRAM). Since NVRAM is non-volatile, when the
Cisco device is turned off, the file remains intact.
 The startup-config files are loaded into RAM each time

22. Configuration files…(Cont’d)
2 The running configuration file
 Once the startup configuration file is loaded into RAM, it
is considered the running configuration or running-config.
 The running configuration is modified when the network
administrator performs device configuration.
 Because the running configuration file is in RAM, it is lost
if the power to the device is turned off or if the device is
restarted.
 Changes made to the running-config file will also be
lost if they are not saved to the startup-config file

23. Configuration files…(Cont’d)

24. Router boot-up process
Step 1 2 3 4
locating
and
loading the
Performing configurati
Loading the Locating and Locating and
on file
the Power- bootstrap loading Cisco loading the
On Self Test program IOS configuration
(POST). file

25. Router boot-up process…(Cont’d)
Performing the Power-On Self Test (POST):
 The Router Performs A POST which is a series of Hardware Test that verify whether all components of the device are
functional.
Loading the bootstrap program:
 After the POST process, the router copies the bootstrap program from ROM into RAM.
 The main purpose of the bootstrap program is to locate the Cisco IOS and load it into RAM.
Locating and loading Cisco IOS:
 The Bootstrap Attempts To Load The IOS From Flash.
 Usually, the IOS is located in the flash memory, but it can also be stored in a TFTP server
 If a full IOS image can not be located, a scaled-down version of the IOS is copied from ROM into RAM.

26. Router boot-up process…(Cont’d)
Locating and loading the configuration file:
After the IOS is loaded, the bootstrap program searches for the startup configuration file (startup-config) in
the NVRAM.
If the file exists, it is copied into RAM as the running configuration file (running-config). if the file does not
exists, the router may serach for a TFTP server.
if the startup configuration file can not be located, the router prompts the user to enter setup mode. setup
mode is a series of questions prompting the user for basic configurations information.
 if the setup mode is not used, the IOS creates a default running-config. this file is a basic configuration file

27. Block diagram of router boot-up process

28. Worldwide market leaders of router

29. Router advantages and issues
Advantages of router:
 ability to share a network connection with multiple machines, which increases productivity.
 Routers deliver the packets of data in an organized way, thus lowering the data load.
 Routers enable a steady and reliable connection between network hosts.
 Routers make use of alternative parts incase the main parts fail to transfer data packets
Router issues:
 Connections can become slow when multiple computers are using a network. This situation is
described as "connection lag ".
 A router basically allows multiple computers to share the same network, which means that the
resources of the network are distributed among the machines, and they may run slower as a result.

30. Any
Question
???