Basics of networking and routing

Presented By :
Owner and Founder of Perfect Training Center
Ethical Hacker
Motivator
Career Councilor

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
(LAN) A Local Area Network (LAN) is a group of computers and
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
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.
In unicast transmissions, a single data packet is sent from a source to a
single destination on the network.

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

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
LAN Infrastructure Devices

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 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
Hubs
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

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
3 3
6 6
Striaght Through cable: used to connect
• switch to switch
• 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

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.
ALL People Seem to Need Data Processing (Layer 7 to 1)
Please Do Not Take Sausage Pizzas Away (Layer 1 to 7)

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
Three different communication modes exists for data
transfer within a session connection:
• Single-duplex
• Half-duplex
• Full-duplex.

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. Main method
for flow control include
•Buffering
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.

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.

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

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

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

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Basics of networking and routing

Basics of networking and routing

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