Introduction to Computer Networking
Welcome to the exciting
world of computer networking and Cisco certification!
There are 3 levels of Cisco certification:
Associate level
CCNA Cisco Certified Network Associate
CCDA Cisco Certified Design Associate
Professional level
CCNP Cisco Certified Network Professional
CCDP Cisco Certified Design Professional
CCSP Cisco Certified Security Professional
CCIP Cisco Certified Internetwork Professional
CCVP Cisco Certified Voice Professional
Expert level
CCIE Cisco Certified Internetwork Expert
- Routing and Switching
- Security
- Service Provider
- Voice
- Storage Networking
- Wireless
- Below are the available paths to become a CCNA:
1 One exam: CCNA (640-802), 50-60 questions,
90 minutes, USD$250.
2 Two exams: ICND1 (640-822), 50-60 questions,
90 minutes, USD$125.
. ICND2 (640-816),
45-55 questions, 75 minute, USD$125.
LAN SETUP
The figure shows the lan configuration in a building with four computers
LAN configuartion using different networks with the help of a router
Most common Internetworking
Models are OSI Reference Model and TCP/IP Model.
Note: OSI – Open Systems Interconnection.
Below
describes the roles and functions of every layer in the OSI reference model:
Application Acts
as the interface between applications and the presentation layer.
Applications
such as web browsers are not reside in this layer. In fact they use
this
interface for communication with remote applications at the other end.
Ex.
Protocols: HTTP, FTP, SMTP, Telnet, SNMP.
Presentation Defines
data formats, presents data, and handles compression and encryption.
As
an example, the FTP ASCII and binary transfer modes define how FTP
transfer
data between 2 end systems. The receiving end will reassemble data
according
to the format used and pass them back to the application layer.
Ex.
Formats: ASCII, EBCDIC, JPEG, GIF, TIFF, MPEG,
WAV, MIDI.
Session Defines how
to setup / establish, control / manage, and end / terminate the
presentation
layer sessions between 2 end systems. Uses port numbers to keep
different
application data separated from each other.
Ex:
SQL, NFS, RPC, X Window, NetBIOS, Winsock,
BSD socket.
Transport Provides
reliable (TCP) and unreliable (UDP) application data delivery
services,
as well as segmentation and reassembly of applications data.
Important
concepts are connection-oriented, connectionless, error
recovery,
acknowledgment,
flow control, and windowing.
Ex.
Protocols: TCP, UDP, SPX (Sequenced Packet Exchange).
Network Defines end-to-end
packet delivery and tracking of end system locations
with
logical addressing – IP addresses. Determines the best path to transfer
data
within an internetwork through the routes learning via routing protocols.
Allows
communication between end systems from different networks.
There
are 2 types of packets – data packets and routing update packets.
Ex.
Protocols: IP, IPX, AppleTalk.
Data Link Defines
how to transmit data over a network media (how to place network layer
packets
onto the network media – cable or wireless) with physical addressing.
Allows
communication between end systems within the same network.
Ex.
Protocols: LAN – Ethernet, WAN – HDLC, PPP, Frame Relay,
ATM.
Physical Defines
specifications for communication between end systems and the physical
media
(how to place data link layer frames onto the media).
Defines
connector shapes, number of pins, pin usages or assignments, electrical
current
levels, and signal encoding schemes. Ex: Ethernet, RS-232, V.35.
Switches and Bridges
Below
lists some comparison points between common network devices:
Routers
They
are Network layer (L3) devices.
Their
main concern is locating specific networks – Where is it? Which is the
shortest
path or best way to reach there?
They
create separate broadcast domains.
Switches and Bridges
They
are Data Link layer (L2) devices.
Their
main role is locating specific hosts within the same network.
Devices
connected to a switch do not receive data that is meant only for
devices
connected to other ports.
They
create separate collision domains for devices connected to them
(segmentation)
but the devices are still reside in the same broadcast domain.
Note: VLAN
technology found in enterprise-class switches are able to create
separate
broadcast domains (multiple networks).
Hubs
They
are Physical layer (L1) devices.
Hubs
are not smart devices. They send all the bits received from one port to all
other
ports; hence all devices connected via a hub receive everything the
other
devices
send. This is like being in a room with many people – everyone hear if
someone
speaks. If there is more than one person speaks at a time, there is only
noise.
Repeaters also fall under the category of L1 devices. All devices
connected
to a hub reside in the same collision and broadcast domains
Below lists the all the UTP categories and their characteristics:
Introduction to Routers
Router is a device which makes communication
possible between two or more different networks present in different
geographical locations.
To make communication possible between two or more
different networks present in the same geographical location, what are the
steps to be taken:
Answer : Configuring a Software Router or
Implementing the CIDR concept
Which Routers to buy ?
Many companies are manufacturing Router :
•
Cisco
•
Nortel
•
Multicom
•
Cyclades
•
Juniper
•
Dlink
•
Linksys
•
3Com
But
Cisco is having monopoly in the market of Routers
Cisco Hierarchical Model
Defined by Cisco to simplify the design, implementation, and maintenance of responsive,
scalable, reliable, and cost-effective networks.
The 3 layers are logical and not physical – there may be many devices in a single layer,
or a single device may perform the functions of 2 layers, eg: core and distribution.
Core layer
Also referred to as the backbone layer. It is responsible for transferring large
amounts of traffic reliably and quickly – switches traffic as fast as possible. A
failure in the core can affect many users; hence fault tolerance is the main
concern in this layer. The core layer should be designed for high reliability,
high availability, high speed, and low convergence. Do not support
workgroup access, implement access lists, VLAN routing, and packet filtering
which can introduce latency to this layer.
Distributionlayer
Also referred to as the workgroup layer. Its primary functions are routing,
Inter-VLAN routing, defining or segmenting broadcast and multicast domains,
network security and filtering with firewalls and access lists, WAN access,
and determining (or filtering) how packets access across the core layer.
Access layer
Also referred to as the desktop layer. Here is where end systems gain access to
the network. The access layer (switches) handles traffic for local services
(within a network) whereas the distribution layer (routers) handles traffic for
remote services. It mainly creates separate collision domains. It also defines the
access control policies for accessing the access and distribution layers.
- In a hierarchical network, traffic on a lower layer is only allowed to be forwarded to the upper
layer after it meets some clearly defined criteria. Filtering rules and operations restrict
unnecessary traffic from traversing the entire network, which results in a more responsive (lower
network congestion), scalable (easy to grow), and reliable (higher availability) network.
- A clear understanding of the traffic flow patterns of an organization helps to ensure the
placement of network devices and end systems within the organization.
ROUTER CLASSIFICATION
FIXED ROUTERS
•
Fixed Router are just like a branded PC where
modification of interfaces is not possible
•
Access Layer Routers are example of Fixed Router
except 1600 and 1700 series
MODULAR ROUTER
•
Modular Router are just like a Assembled PC where
modification of interfaces is possible
•
Distribution and Core Layer Routers example of
Modular Router
Ports of Router
Attachment Unit Interface
•
AUI pin configuration is 15 pin female.
•
It is known as Ethernet Port or LAN port or Default Gateway.
•
It is used for connecting LAN to the Router.
•
Transceiver is used for converting 8 wires to 15
wires. i.e. RJ45 to 15 pin converter.
Attachment Unit Interface
If both sides of a cable are connected with different devices the crimping has to in straight order
color coding for the straight crimping order
If the computer is directly connected to the router the color coding has to cross over
ie:
color coding for the Cross over crimping order
Serial Port
•
Serial pin configuration is 60 pin
configuration female (i.e. 15 pins
and 4 rows) and Smart Serial pin configuration
is 26 pin configuration female.
•
It is known as WAN Port
•
It is used for connecting to Remote Locations
V.35 cable is having 60 pin configuration male at
one end and on the other end 18 pin configuration male
Console Port
•
It is known as Local Administrative Port
•
It is generally
used for Initial Configuration, Password Recovery and Local
Administration of the Router. It is RJ45 Port
•
IMP : It is the most delicate port on the Router. So
make less use of the Console Port.
Console Connectivity
•
Connect a rollover cable to the router console port
(RJ-45 connector).
•
Connect the other end of the rollover cable to the
RJ-45 to
DB-9 converter
•
Attach the female DB-9 converter to a PC Serial Port.
•
Open Emulation Software
Auxiliary Port
•
It is
known as Remote Administrative Port.
•
Used for
remote administration
•
Its an
RJ-45 port
•
A
console or a rollover cable is to be used.
Other Ports
• BRI Port
Basic
Rate Interface used to connect ISDN to the Router. It is a RJ45 Port. It is available on 2503 and 2520 model
router.
•
10 Base T Port
It is
a RJ45 Port and used for connecting LAN to the Router. Its function is same as
the AUI Port but there is no need for a Transceiver. It is available on 2520
model router.
Brief Overview
•
WAN interfaces
–
Serial interface (S0, S1 etc) – 60 pin/26 pin(smart
serial)
–
ISDN interface(BRI0 etc) – RJ45
–
LAN interfaces - Ethernet
–
AUI (Attachment Unit Interface) (E0)– 15 pin
–
10baseT – RJ45
–
Administration interfaces
–
Console – RJ45 - Local
–
Auxiliary – RJ45 – Remote
Internal Components
ROM
A bootstrap program is located here. It is same as the BIOS of the
PC. Bootstrap program
current version is 11.
FLASH
Internetwork Operating System (IOS) developed by Cisco is
stored here. IOS is
Comman line interface. NVRAM
Non volatile RAM, similar
to Hard Disk
It is also known as
Permanent Storage or Startup Configuration. Generally size of NVRAM is 32 KB.
RAM
It is also known as Temporary Storage or running Configuration.
Minimum size of RAM is 2MB. The size of RAM is greater than NVRAM in the Router.
Processor
Motorola Processor 70 Mhz,
RISC based processor
(Reduced Instruction Set Computer)
Router
Classification
BOOT sequence
