Basics Of Networking (Overview)

Basics Of Networking

Ashiesh Aryan

What is a Computer Network?
A network is a collection of computers, printers, routers, switches, and other
devices that are able to communicate with each other over some
transmission media.

Types of Networks
There are two basic types of networks currently in existence:
A Local Area Network (LAN)

A Wide Area Network (WAN)

Local Area
Networks A Local Area Network (LAN) is a group of computers and
(LAN) network communication devices within a limited geographic
area, such as an office building. No third party involvement here.
They are characterized by the following:
• High data transfer speeds
• Generally less expensive technologies
• Limited geographic area

Wide Area
Networks
(WAN) A Wide Area Network (WAN) interconnects LANs. It is not
restricted to a particular geographic area and may be
interconnected around the world. Third party network is involved.
They are characterized by the following:
• Multiple interconnected LANs
• Generally more expensive technology
• More sophisticated to implement than LANs
• Exist in an unlimited geographic area
• Less error resistance due to transmission travel distances

Common LAN Topologies
Bus Architecture In a bus topology:
• a single cable connects each
workstation in a linear, daisy-chained
fashion.

•signals are broadcasted to all
stations, but stations only act on the
frames addressed to them.

Ring Architecture
•In a ring topology:

•Unidirectional links connect the
transmit side of one device to the
receive side of another device.
•Devices transmit frames to the next
device (downstream member) in the
ring.

Star Topology

In a star topology, each station is connected to a central
hub or concentrator that functions as a multi-port
repeater. Each station broadcasts to all of the devices
connected to the hub. Physical LAN topologies are
usually characterized as either bus or ring.

LAN Transmission Methods
LAN transmission methods fall into 3 main categories:
• Unicast transmission
• Multicast transmission
• Broadcast transmission

Unicast Transmission
In unicast transmissions, a single data packet is sent from a source to a
single destination on the network.

Unicast Process

• The source addresses
the packet with the
destination address.
• The packet is sent into
the network.
• The network delivers the
packet to the destination.

Multicast Transmission
In multicast transmissions, a single data packet is copied and sent to
specific destinations on the network

Multicast Process

• The source addresses the packet
using a multicast address.
• The packet is sent into the
network.
• The network copies the packet.
• A copy is delivered to each
destination that is included in the
multicast address.

Broadcast Tranmission
In multicast transmissions, a single data packet is copied and sent to
specific destinations on the network

Broadcast Process

• The source addresses the packet with the broadcast address.
• The packet is sent into the network.
• The network copies the packet.
• The packet copies are delivered to all destinations on the
network.

LAN Infrastructure Devices

There are numerous devices associated with data
information flow across a LAN. When adjoined, they create
the infrastructure of a functional LAN. These devices
include:

•Repeaters

•Bridges

•Hubs

•Switches

•Routers

Repeaters
Repeaters, located within the physical layer of a network, regenerate and
propagate signals from one to another. They do not change any information
being transmitted, and they cannot filter any information. Repeaters help to
extend the distances of networks by boosting weak signals.
Bridges
Bridges are intelligent repeaters. They regenerate
transmitted signals, but unlike repeaters, they can also
determine destinations.

Hubs Hubs connect all computer LAN connections into one
device. They are nothing more than multiport repeaters.
Hubs cannot determine destinations; they merely
transmit to every line attached in a half-duplex mode.

Routers Routers are a step up from bridges. They are able to
route and filter information to different networks. Some
routers can automatically detect problems and redirect
information around the problem area. These are called
"intelligent routers."

Switches
Switches connect all computer LAN connections, the
same as hubs do. The difference is that switches can run
in full-duplex mode and are able to direct and filter
information to and from specific destinations.

WAN
WAN Infrastructure

As with LANs, there are numerous devices associated with data information
flow across a WAN. Together, these devices create the infrastructure of a
functional WAN. These devices include:
•Router
•ATM Switch
•Modem and CSU/DSU
•Communication Server
•Multiplexer
•X.25/Frame Relay Switches

ATM Switches

ATM Switches provide high-speed transfer
between both LANs and WANs.

Modem (modulator / demodulator)

Modems convert digital and analog signals. At the source, modems convert
digital signals to a form suitable for transmission over analog communication
facilities (public telephone lines). At the destination, modems convert the signal
back to a digital format.
CSU/DSU (Channel Service Unit / Data Service Unit)
CSUs/DSUs are similar to modems, however they send data in digital format
across digital telephone loops. They are usually in a physical box, but they may
come in two separate units: CSUs or DSUs.

Multiplexers

A Multiplexer combines multiple signals for
transmission over a single circuit. This allows
for the transfer of various data simultaneously,
such as video, sound, text, etc.

Communication Servers

Communication Servers are typically dial in/out servers that allow users
to dial in from remote locations and attach to the LAN.

X.25 / Frame Relay Switches

X.25 and Frame Relay Switches connect private data over public data circuits
using digital signal. These units are very similar to ATM switches, but the
transfer rate of data is not comparable.

Local Area Network Cabling

The earliest LANs used coaxial cables. Over time, the
twisted pair cables used in telephone systems were
improved to carry higher frequencies and support LAN
traffic. More recently, fiber optic cables have emerged as a
high-speed cabling option.
Local Area Networks use four types of cables:

•Coaxial

•Unshielded Twisted Pair (UTP)

•Shielded Twisted Pair (STP)

•Fiber Optic

Coaxial Cables
A coaxial cable consists of:
•a single copper conductor
•a layer of shielding with a
ground wire
•an outer jacket
Coaxial cables are sometimes
used for bus topologies, but
many LAN products are
dropping support of coaxial
cable connectivity.
The Ethernet LAN protocol was originally developed to operate over coaxial
cables.
10Base5 / Thicknet cable:
•was the original Ethernet cable.
•is no longer in use in modern LANs.
10Base2 / Thinnet cable:
has a smaller diameter than Thicknet.
•replaced Thicknet.
•is no longer recommended, but is still used in some very small LANs.

Unshielded Twisted Pair
Unshielded twisted pair (UTP) cable is used
for both LANs and telephone systems. UTP
cables are composed of four color-coded
pairs of copper conductors twisted around
each other. An outer jacket provides
protection and keeps the pairs in alignment.
UTP cable connects to devices via 8 pin
modular connectors called RJ-45 plugs. All
LAN protocols can operate over UTP. Most
modern LAN devices are equipped with RJ-45
jacks.
Shielded Twisted Pair
STP cable is also used for Data
Networks. It originated with IBM's
Token-Ring networks. Its shielding
allows greater tolerances for
protection from EMI interference,
such as from flourescent light
fixtures and electric motors.

Fiber Optic Cable
Fiber Optic cables are the latest
development in cabling technology.
They are constructed from optical
glass. There is a central glass
filament, called the core, and
surrounding layers of cladding, buffer
coatings, strengthening materials, and
an outer jacket.

Information is transmitted by wavelengths of light. This is accomplished through
devices that convert electrical signals into rapid pulses of either LED or Laser
light.
Fiber optic cables offer several advantages, including:
• high bandwidth capacity (many gigabits per second).
• longer distances between devices (from 2 to over 60 kilometers).
• immunity to electromagnetic interferences
Fiber optic cables are widely used in WANs for both voice and data
communications. The primary barrier to their widespread use in LANs is the
cost of electronics.

Ethernet
Ethernet was developed by Xerox in 1970. It was implemented through
thicknet cable running at 10 Mbps.
Ethernet is a connection media access method that allows all hosts on a
network to share the same bandwidth of a link.
Ethernet actually just refers to the LAN implementations that includes three
principal categories.
• Ethernet / IEEE 802.3---operates at 10 Mbps on coaxial cable and twisted
pair cable.
• 100-Mbps Ethernet---(also known as Fast Ethernet) operates at 100 Mbps
over twisted-pair cable.
• 1000-Mbps Ethernet---( also known as Gigabit Ethernet) operates at 1000
Mbps (1 Gbps) over fiber and twisted-pair cables.

Basic Operation
Ethernet and IEEE 802.3 operation involves three basic components:
• Transmission
• Media access
• Collision handling

Media Access
The Ethernet media access uses the following process:
• Any station on a LAN can access the network at any time.
• Before sending data, stations listen for traffic on the network.
• A station waits until it detects no traffic before it transmits data.
Collision handling
Ethernet is a "first come, first serve" environment. In such an environment,
any station on the network can transmit whenever the network is quiet. A
collision occurs when two stations listen for traffic, hear none, and then
transmit data at the same time. Both transmissions are damaged, and the
stations must retransmit at a later time.
CSMA / CD

Ehernet Cabling
Striaght Through cable: used to connect
• Host to switch or hub
•Router to switch or hub
Four wires are used in straight-through cable to connect Ethernet devices.

1 1
2 2
Cross Through cable: used to connect 3 3
• switch to switch 6 6
• Router direct to host
• hub to hub
• Host to host
Four wires are used as in straight-through cable to connect Ethernet devices.

1 1
2 2
3 3
6 6

Rolled cable

Although rolled cable is not used to connect any Ethernet connections
together, we use this cable to connect a host to a router console serial
communication (com) port.
Eight wires are used in this cable to connect serial devices.

1 1
2 2
3 3
4 4
5 5
6 6
7 7
8 8

Start HyperTerminal to create a console connection and configure the device.
Start Programs accessories communications HyperTerminal
Provide the default settings for com1 port

Network Model Overview
In order for a computer to send information to another computer, and for
that computer to receive and understand the information, there has to exist
a set of rules or standards for this communication process. These
standards ensure that varying devices and products can communicate with
each other over any network. This set of standards is called a model.
Network Model Advantages
This division provides advantages for the network design, architecture and
implementation. These include:

•Reduces complexity - by dividing the processes into groups, or layers,
implementation of network architecture is less complex
•Provides compatibility - standardized interfaces allow for "plug-and-play"
compatibility and multi-vendor integration
•Facilitates modularization - developers "swap" out new technologies at
each layer keeping the integrity of the network architecture
•Accelerates evolution of technology - developers focus on technology at
one layer while preventing the changes from affecting another layer
•Simplifies learning - processes broken up into groups divides the
complexities into smaller, manageable chunks

Basics Of Networking (Overview)

OSI Network Model
There are 7 layers in the OSI
model. Each layer is
responsible for a particular
aspect of data communication.
For example, one layer may be
responsible for establishing
connections between devices,
while another layer may be
responsible for error checking
during transfer.

The layers of the OSI model are divided into two groups: the upper layer
and lower layer. The upper layers focus on user applications and how files
are represented on the computers prior to transport. For the most part,
network engineers are more concerned with the lower layers. It's the lower
layers that concentrate on how the communication across a network
actually occurs.

The Application Layer
The Application Layer is the highest layer in the
protocol stack and the layer responsible for
introducing data into the OSI stack. In it resides the
protocols for user applications that incorporate the
components of network applications.
Classification of Applications
Computer applications
Network applications
Internetwork applications

Examples: Telnet, FTP, HTTP, WWW Browsers,
NFS, SMTP, POP, TFTP .

Presentation Layer

The Presentation Layer manipulates the
representation of data for transfer to applications on
different devices.

The Presentation Layer is responsible for the
following services:
• Data representation
• Data security
• Data compression

Data Representation

Session Layer

The Session Layer establishes, manages, and
terminates sessions (different from connections)
between applications as they interact on different hosts
on a network.
Its main job is to coordinate the service requests and
responses between different hosts for applications.
Examples: NFS, SQL, RPC, ASP

Transport Layer

The basic roles of the Transport Layer are to establish end-to-end
connections from one computer to another on the network and provide
reliable "transport" of data between devices.

Basic Transport Layer Services:
Resource Utilization (multiplexing)
Connection Management (establishing)
Flow Control (Buffering / Windowing)
Reliable Transport (positive acknowledgment / error checking)

Flow Control
Once the connection has occurred and transfer is in progress, congestion
of the data flow can occur at a destination for a variety of reasons. Possible
options include:
The destination can become overwhelmed if multiple devices are trying to
send it data at the same time.
It may become overwhelmed if the source is sending faster than it can
physically receive.

Congestion Prevention
The Transport Layer is responsible for providing flow control to alleviate the
issue of congestion and provide reliability in the data transfer. Two main
methods for flow control include
•Buffering
•Windowing

Buffering
Buffering is a form of data flow control regulated by the Transport Layer. It is
responsible for ensuring that sufficient buffers are available in the
destination for the processing of data and that is data transmitted at a rate
that does not exceed what the buffer can handle.

Windowing
Windowing is a flow control scheme in which the source computer will monitor
and make adjustments to the amount of information sent based on
successful, reliable receipt of data segments by the destination computer.
The size of the data transmission, called the "window size", is negotiated at
the time of connection establishment. It is determined by the amount of
memory or buffer that is available.

Given a window size of 3, the source
(in this case a router) sends 3 data
segments to the destination. The
destination sends an acknowledgement
asking for the next set of data
segments.

If the destination does not receive all
three of the negotiated data segments,
for example, due to a buffer overflow, it
sends no acknowledgment. Since the
source does not receive an
acknowledgment, it knows the data
segments should be retransmitted

Network Layer
The Network Layer is the 3rd layer in the OSI model and is responsible for
identifying computers on a network. This layer works closely with layer 2 to
translate data packets from a logical address (similar to an IP address) into
hardware based MAC addresses.
This layer is concerned with 2 functions:
• Routing
• Fragmentation / Reassembly

Two types of packets are used at the Network layer:

Data packets: Used to transport user data through the internetwork.
Protocols used to support data traffic are called routed protocols. Eg. IP
and IPX.

Route update packets: Used to update neighboring routers about the
network connected to all routers within the internetwork. Protocols that
send route updates are called routing protocols. Eg. RIP, EIGRP, OSPF

Data Link / Physical Layer
LAN and WAN protocols occupy the bottom two layers of the OSI model.
These two layers, Physical Layer and Data Link Layer, work very closely
together to ensure data transfer across the physical network. Examples:
HDLC, Frame Relay, PPP, ATM, FDDI, IEEE 802.3/802.2
To accomplish accurate delivery, the Data Link Layer provides the following
services:
1. Machine address determination of both sending and receiving machines
2. Formatting of Network Layer "packets" into frames with machine
addresses
attached
3. Sequencing and resequencing of frames transmitted out of sequence
Data Link Sublayers

Logical Link Control (LLC)
responsible for identifying Network
layer protocols and encapsulating
them.
Media Access Control (MAC) defines
how packets are placed on media

Physical Layer

The Physical Layer is the lowest layer in the OSI model and is concerned
with how the physical structure of the network enables transmission of
data. It is responsible for defining the mechanical and electrical
specifications for the transmission medium within a connection, as well
as the transformation or encoding of data into “bits”.
Examples:EIA/TIA-232, V.35, EIA/TIA-449, RJ-45, Ethernet, 802.3
Protocols

Protocols defined at the Physical Layer standardize physical
connections. Specifications include voltage levels, maximum
transmission distances, data rates, and physical connectors.

Each layer depends on the service
function of the ISO/OSI layer below it.
To provide this service, the lower
layer uses encapsulation to put the
PDU from the upper layer into its
data field; then it can add whatever
headers and trailers the layer will use
to perform its function.

As networks perform services for
users, the flow and packaging of
the information changes. In this
example of internetworking, five
conversion steps occur:

What do the 7 layers really do?

TCP/IP
The Transmission Control Protocol/Internet Protocol (TCP/IP) suite of
protocols was developed as part of the research done by the Defense
Advanced Research Projects Agency (DARPA).
TCP/IP Protocol Layers
• Process/Application Layer
• Transport Layer or Host-to-Host Layer
• Internet Layer
• Network Access Layer

Application protocols exist
for file transfer, e-mail,
and remote login.
Network management is
also supported at the
application layer.

Transport services allow
users to segment and
reassemble several upper-
layer applications onto the
same transport-layer data
stream.

TCP Segment

UDP Segment

IP provides connectionless,
best-effort delivery routing of
datagrams. It is not concerned
with the content of the
datagrams. Instead, it looks for
a way to move the datagrams to
their destination.

IP Datagram

Version - Version number (4 bits)
Header Length - Header length in 32-
bit words (4 bits)
Priority and Type of Service - How the
datagram should be handled. The first 3
bits are priority bits (8 bits).
IP Options - Network testing,
debugging, security, and others (0 or 32
bits if any)

ICMP
The Internet Control Message Protocol (ICMP) is implemented by all
TCP/IP hosts. ICMP messages are carried in IP datagrams and are used to
send error and control messages.

ICMP uses the following types of defined messages:
1. Destination Unreachable
2. Time Exceeded
3. Parameter Problem
4. Subnet Mask Request
5. Redirect
6. Echo
7. Echo Reply
8. Information Request
9. Information Reply
10.Address Request
11.Address Reply

Address Resolution Protocol
Address Resolution Protocol (ARP) is used to resolve or map a known IP
address to a MAC sublayer address to allow communication on a multi-
access medium such as Ethernet.

The term local ARP is used to describe resolving an address when both the
requesting host and the destination host share the same media or wire.

Reverse ARP
Reverse Address Resolution Protocol (RARP) relies on the presence of a
RARP server with a table entry or other means to respond to these requests.

ARP and RARP are implemented directly on top of the data link layer

IP Address
In a TCP/IP environment, end stations communicate seamlessly with
servers or other end stations. This communication occurs because each
node using the TCP/IP protocol suite has a unique 32-bit logical IP address.
Each IP datagram includes the source IP address and destination
IP address that identifies the source and destination network and host.

When IP was first developed, there were no classes of addresses.
Now, for ease of administration, the IP addresses are broken up into
classes.

The bits in the first octet
identify the address
class. The router uses
the first bits to identify
how many bits it must
match to interpret the
network portion of the
address

Class A addresses include the following:
• The first bit is 0.
• Range of network numbers: 1.0.0.0 to

126.0.0.0
• Number of possible networks: 127 (1-
126 usable, 127 is reserved)
• Number of possible values in the host

portion: 16,777,216.

Class B addresses include the following:
•The first two bits are 10.
•Range of network numbers: 128.0.0.0 to
191.255.0.0
•Number of possible networks: 16,384
•Number of possible values in the host
portion: 65,536

Class C addresses include the following:
•The first three bits are 110.
•Range of network numbers: 192.0.0.0 to
223.255.255.0
•Number of possible networks: 2,097,152
•Number of possible values in the host
portion: 256

Class D addresses include the
following:
• Range of network numbers:
224.0.0.0 to 239.255.255.255

•Planning IP Addressing

• Addressing Guidelines

Addressing Guidelines
IP Address are by TCP/IP v-4.0

There are 5 Classes of IP Addressing

Class A, B & C are used for General Networking

Class D is for Multicasting Purpose

Class E is for IETF’s own use

IP Address has two Part:-
1. Network
2. Host

The First Number in the Network ID Cannot Be 127

The Host ID Cannot Be All 255s

The Host ID Cannot Be All Zeros

IP Addresses are Represented in Dotted Decimal Format

Dotted Decimal is by Four Octet (w.x.y.z)

IP v-4.0 is 32 bit Addressing Format

1st Octet (w) is for the Identification of Class

Each Octet have 8 bit value

The Values are from 0-255 in each octet

•The Subnet Mask is used to Identify the Network Part

•The Network ID should be Constant for a Particular Network

The Host ID Must Be Unique to the Local Network ID

Major Components of a Router
• Random access memory (RAM)
contains the software and data
structures that allow the router to
function. The principle software
running in RAM is the Cisco IOS
image and the running
configuration.
• Read-only memory contains
microcode for basic functions to
start and maintain the router.
• Flash is primarily used to contain the IOS software image. Some routers
run the IOS image directly from Flash and do not need to transfer it to RAM.

• Non-volatile random access memory is mainly used to store the
configuration. NVRAM uses a battery to maintain the data when power is
removed from the router.

•Configuration Register The configuration register is used to control how the
router boots up.

Overview of Cisco Device Startup
• This event is a series of
hardware tests to verify
that all components of
the router are
functional. POST
executes from
microcode resident in
the system ROM.
• Bootstrap code is used
to perform subsequent
events like finding the
IOS software, loading
it, and then running it.
3. The bootstrap code determines where the IOS software to be run is
located. The configuration register, configuration file, or Flash memory
are the normal places to house the IOS image.
4. Once the bootstrap code has found the proper image, it then loads that
image into RAM and starts the IOS running
5. The default is to look in NVRAM for a valid configuration.
6. The desired configuration for the router is loaded and executed.

Setup: The Initial
Configuration Dialog

Router#setup

--- System Configuration Dialog ---

Continue with configuration dialog? [yes/no]: yes
At any point you may enter a question mark '?' for help.
Use ctrl-c to abort configuration dialog at any prompt.
Default settings are in square brackets '[]'.

Basic management setup configures only enough connectivity
for management of the system, extended setup will ask you
to configure each interface on the system

Would you like to enter basic management setup? [yes/no]: no

Setup Interface Summary

First, would you like to see the current interface summary? [yes]:

Interface IP-Address OK? Method Status Protocol

BRI0 unassigned YES unset administratively down down

BRI0:1 unassigned YES unset administratively down down

BRI0:2 unassigned YES unset administratively down down

E0 unassigned YES unset administratively down down

Serial0 unassigned YES unset administratively down down

Setup Initial
Global Parameters

Configuring global parameters:

Enter host name [Router]:wg_ro_c

The enable secret is a password used to protect access to
privileged EXEC and configuration modes. This password, after
entered, becomes encrypted in the configuration.
Enter enable secret: cisco

The enable password is used when you do not specify an
enable secret password, with some older software versions, and
some boot images.
Enter enable password: sanfran

The virtual terminal password is used to protect
access to the router over a network interface.
Enter virtual terminal password: sanjose
Configure SNMP Network Management? [no]: Configure LAT? [yes]: no
Configure AppleTalk? [no]:
Configure DECnet? [no]:
Setup Initial Configure IP? [yes]:
Protocol Configurations Configure IGRP routing? [yes]: no
Configure RIP routing? [no]:
Configure CLNS? [no]:
Configure IPX? [no]:
Configure Vines? [no]:
Configure XNS? [no]:
Configure Apollo? [no]:

Setup Interface
Parameters
BRI interface needs isdn switch-type to be configured
Valid switch types are :
[0] none..........Only if you don't want to configure BRI.
[1] basic-1tr6....1TR6 switch type for Germany
[2] basic-5ess....AT&T 5ESS switch type for the US/Canada
[3] basic-dms100..Northern DMS-100 switch type for US/Canada
[4] basic-net3....NET3 switch type for UK and Europe
[5] basic-ni......National ISDN switch type
[6] basic-ts013...TS013 switch type for Australia
[7] ntt...........NTT switch type for Japan
[8] vn3...........VN3 and VN4 switch types for France
Choose ISDN BRI Switch Type [2]:

Configuring interface parameters:

Do you want to configure BRI0 (BRI d-channel) interface? [no]:

Do you want to configure Ethernet0 interface? [no]: yes
Configure IP on this interface? [no]: yes
IP address for this interface: 10.1.1.33
Subnet mask for this interface [255.0.0.0] : 255.255.255.0
Class A network is 10.0.0.0, 24 subnet bits; mask is /24

Do you want to configure Serial0 interface? [no]:

Router User-Mode
Command List

Router>?
Exec commands:
access-enable Create a temporary Access-List entry
atmsig Execute Atm Signalling Commands
cd Change current device
clear Reset functions
connect Open a terminal connection
dir List files on given device
disable Turn off privileged commands
disconnect Disconnect an existing network connection
enable Turn on privileged commands
exit Exit from the EXEC
help Description of the interactive help system
lat Open a lat connection
lock Lock the terminal
login Log in as a particular user
logout Exit from the EXEC
-- More --

Router Privileged-Mode
Command List
Router#?
Exec commands:
access-enable Create a temporary Access-List entry
access-profile Apply user-profile to interface
access-template Create a temporary Access-List entry
bfe For manual emergency modes setting
cd Change current directory
clear Reset functions
clock Manage the system clock
configure Enter configuration mode
connect Open a terminal connection
copy Copy from one file to another
debug Debugging functions (see also 'undebug')
delete Delete a file
dir List files on a filesystem
disable Turn off privileged commands
disconnect Disconnect an existing network connection
enable Turn on privileged commands
erase Erase a filesystem
exit Exit from the EXEC
help Description of the interactive help system
-- More --

Enhanced Editing Commands
(Automatic scrolling of long lines.)
Ctrl-A Move to the beginning of the command line.
Ctrl-E Move to the end of the command line.
Esc-B Move back one word.
Esc-F Move forward one word.
Ctrl-B Move back one character.
Ctrl-F Move forward one character.
Ctrl-D Delete a single character.

Ctrl-P or Up Arrow Recalls last (previous) commands

Ctrl-N or Down Arrow Recalls more recent commands

show history Shows command buffer contents

history size line Sets the buffer size permanently

terminal history size lines Sets session command buffer size

Examining the Register Configuration
The configuration register is a 16-bit register. The lowest four bits of the
configuration register (bits 3, 2, 1, and 0) form the boot field.

You can change the default configuration register setting with the enabled
config-mode config-register command.

Examining the IOS Copy Command

Router#show flash
System flash directory:
File Length Name/status
1 10084696 c2500-js-l_120-3.bin
[10084760 bytes used, 6692456 available, 16777216
total]
16384K bytes of processor board System flash (Read
ONLY)
Router#copy tftp flash
Address or name of remote host? 10.1.1.1
Source filename? c2500-js-l_120-3.bin
Accessing tftp://10.1.1.1/c2500-js-l_120-3.bin...
Erase flash befor copying? [Enter]
Erasing the flash filesystem will remove all files!
Continue? [Enter]
Erasing device... eeeee(output omitted) ...erased
Erase of flash: complete
Loading c2500-js-l_120-3.bin from 10.1.1.1 (via
Ethernet0): !!!!!!!!!!!!!!!!!!!!
(output omitted)
[OK - 10084696/20168704 bytes]
Verifying checksum... OK (0x9AA0)
10084696 bytes copied in 309.108 secs (32636
bytes/sec)

The following example demonstrates the sequence of commands you would
enter to configure various passwords on a router with the following
characteristics:
Console password is cisco
Telnet password is cisco
Privileged Mode password is cisco
Secret password is cisco
Router(config)#line console 0
Router(config-line)#login
Router(config-line)#password cisco
Router(config-line)#exit
Router(config)#line vty 0 4
Router(config-line)#login
Router(config-line)#password cisco
Router(config-line)#exit
Router(config)#enable password ccna
Router(config)#enable secret cisco
Router(config)#service password-encryption

interface Command Syntax
router(config)#interface ethernet 1
router(config-if)#ip address 10.1.1.1 255.0.0.0
router(config-if)#no shut

The following example demonstrates the sequence of
commands you would enter to configure a serial line on a router
with the following characteristics:
Router interface is serial 0
Clock Rate is 64000
Bandwidth is 64 kbits
Router#configure terminal
Router(config)# interface serial 0
Router(config-if)#clock rate 64000
Router(config-if)#bandwidth 64
Router(config-if)# exit
Router(config)# exit
Router# show interface serial 0
Serial 0 is up, line protocol is up
Hardware is HD64570... MTU 1500 bytes, BW 64000
Kbit,...
Serial Interface show controller Command

Routing is the process by which an item gets from one location to another.
Many items get routed: for example, mail, telephone calls, and trains. In
networking, a router is the device used to route traffic.
Key Information a Router Needs
Destination Address - What is the destination (or address) of the item that
needs to be routed?
Identifying sources of information - From which source (other routers) can
the router learn the paths to given destinations?
Discovering routes - What are the initial possible routes, or paths, to the
intended destinations?
Selecting routes - What is the best path to the intended destination?
Maintaining routing information - A way of verifying that the known paths to
destinations are the most current.

•Routed protocols - Any network protocol that provides enough
information in its network layer address to allow a packet to be
forwarded from host to host based on the addressing scheme. Routed
protocols define the format and use of the fields within a packet.
Packets generally are conveyed from end system to end system. The
Internet protocol IP is an example of a routed protocol.

Here are some examples of Routed Protocols:
• Internet Protocol (IP)
• AppleTalk (AT)
• Novell NetWare Protocol
• Xerox Network Systems (XNS)

•Routing protocols - Supports a routed protocol by providing
mechanisms for sharing routing information. Routing protocol messages
move between the routers. A routing protocol allows the routers to
communicate with other routers to update and maintain tables.
examples of routing protocols are RIP,IGRP,EIGRP and OSPF.

Types of Routing
The different types of routing are:
• Static routing
• Default routing
• Dynamic routing

Static Routing

Routes learned by the router when an administrator manually establishes
the route. The administrator must manually update this static route entry
whenever an internetwork topology change requires an update.
Benefits:
• There is no overhead on the router CPU.
• There is no bandwidth usage between routers
• It adds security
Disadvantage:
•The administrator must really understand the internetwork and how
each router is connected to configure routes correctly.
• If a network is added to internetwork, the administrator has to add route to

it on all routers-by hand

Default Routing
A default route is a special type of static route. A default route is a route
to use for situations when the route from a source to a destination is not
known or when it is unfeasible for the routing table to store sufficient
information about the route.

In the image, Cisco B is configured to forward all frames for which the
destination network is not explicitly listed in its routing table to Cisco A.

Basics Of Networking (Overview)

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