Transcript Where Have We Been? - IIS Windows Server

Institute of Technology Sligo - Dept of Computing
THE OSI MODEL
Application
Presentation
Session
Transport
Network
Data-Link
Physical
Where We’ve
Been
Chapter 1—Review
Paul Flynn
Institute of Technology Sligo - Dept of Computing
Table of Contents
Go There!

Enterprise
Go There!

Review the OSI Model

Encapsulation

LAN Devices &
Technologies

Transport Layer

IP Addressing
Go There!
Go There!
Go There!
Go There!
Institute of Technology Sligo - Dept of Computing
A New Word!—Enterprise
A corporation, agency,
school, or other
organization that works
to tie together its data,
communication,
computing, and file
servers.
Institute of Technology Sligo - Dept of Computing
Your Job as a Network Guru

Help Enterprises meet their needs by:



Interconnecting their LANs so that geographically
remote services can be accessed
Ensuring users get high bandwidth access over their
LANs (i.e. Replacing hubs with switches; 10Mbps
NICs with 10/100 Mbps NICs)
Implementing new technologies as they emerge like
e-commerce, video conferencing, voice over IP, and
distance learning.
Institute of Technology Sligo - Dept of Computing
THE OSI MODEL
Application
Presentation
Review The Model
Session
Transport
Network
Data-Link
Physical
Open Systems
Interconnected
Reference Model
Table of Contents
Institute of Technology Sligo - Dept of Computing
Why A Layered Model?
Application

Presentation

Session

Transport
Network

Data-Link
Physical


Reduces complexity
Standardizes interfaces
Facilitates modular
engineering
Ensures interoperable
technology
Accelerates evolution
Simplifies teaching & learning
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Host Layers vs. Media Layers
Application
Host Layers
Presentation
Provides accurate
data delivery
between computers
Session
Transport
Network
Data-Link
Physical
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Host Layers vs. Media Layers
Application
Presentation
Session
Transport
Network
Data-Link
Physical
Media Layers
Controls physical
delivery of the message
over the network
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Application Layer
Application

Presentation
Session

Transport
Network
Data-Link
Physical

Provides network services
(processes) to applications.
For example, a computer on a
LAN can save files to a server
using a network redirector
supplied by NOSs like Novell.
Network redirectors allow
applications like Word and
Excel to “see” the network.
Institute of Technology Sligo - Dept of Computing
Presentation Layer
Application
Presentation


Session
Transport
Network
Data-Link
Physical

Provides data representation
and code formatting.
Code formatting includes
compression and encryption
Basically, the presentation
layer is responsible for
representing data so that the
source and destination can
communicate at the
application layer.
Institute of Technology Sligo - Dept of Computing
Session Layer
Application

Presentation
Session

Transport
Network
Data-Link
Physical

Provides inter-host communication
by establishing, maintaining, and
terminating sessions.
Session uses dialog control and
dialog separation to manage the
session
Some Session protocols:






NFS (Network File System)
SQL (Structured Query Language)
RCP (Remote Call Procedure)
ASP (AppleTalk Session Protocol)
SCP (Session Control Protocol)
X-window
Institute of Technology Sligo - Dept of Computing
Transport Layer
Application

Presentation
Session

Transport
Network
Data-Link

Physical


Provides reliability, flow control, and
error correction through the use of
TCP.
TCP segments the data, adding a
header with control information for
sequencing and acknowledging
packets received.
The segment header also includes
source and destination ports for
upper-layer applications
TCP is connection-oriented and
uses windowing.
UDP is connectionless. UDP does
Institute of Technology Sligo - Dept of Computing
Network Layer
Application

Presentation
Session

Transport
Network

Data-Link
Physical

Responsible for logically
addressing the packet and path
determination.
Addressing is done through routed
protocols such as IP, IPX,
AppleTalk, and DECnet.
Path Selection is done by using
routing protocols such as RIP,
IGRP, EIGRP, OSPF, and BGP.
Routers operate at the Network
Layer
Institute of Technology Sligo - Dept of Computing
Data-Link Layer


Application
Presentation
Session
Transport

Network
Provides access to the media
Handles error notification,
network topology issues, and
physically addressing the
frame.
Media Access Control
through either...
Data-Link

Physical


Deterministic—token passing
Non-deterministic—broadcast
topology (collision domains)
Important concept: CSMA/CD
Institute of Technology Sligo - Dept of Computing
Physical Layer

Application
Presentation
Session
Transport
Network
Data-Link
Physical

Provides electrical,
mechanical, procedural and
functional means for
activating and maintaining
links between systems.
Includes the medium through
which bits flow. Media can
be...




CAT 5 cable
Coaxial cable
Fiber Optics cable
The atmosphere
Institute of Technology Sligo - Dept of Computing
THE OSI MODEL
Application
Presentation
Encapsulation
Session
Transport
Network
Data-Link
Peer-to-Peer
Communications
Physical
Table of Contents
Institute of Technology Sligo - Dept of Computing
Peer-to-Peer Communications

Peers communicate using the PDU of their
layer. For example, the network layers of the
source and destination are peers and use
packets to communicate with each other.
Application
Data
Application
Presentation
Data
Presentation
Session
Session
Transport
Data
Segments
Transport
Network
Packets
Network
Data-Link
Frames
Data-Link
Physical
Bits
Physical
Institute of Technology Sligo - Dept of Computing
Encapsulation Example
Application

Presentation
Session
Transport

Network
Data-Link
Physical

You type an email message.
SMTP takes the data and
passes it to the Presentation
Layer.
Presentation codes the data
as ASCII.
Session establishes a
connection with the
destination for the purpose
of transporting the data.
Institute of Technology Sligo - Dept of Computing
Encapsulation Example

Application
Presentation
Session
Transport


Network
Data-Link
Physical

Transport segments the
data using TCP and hands it
to the Network Layer for
addressing
Network addresses the
packet using IP.
Data-Link then encaps. the
packet in a frame and
addresses it for local
delivery (MACs)
The Physical layer sends
the bits down the wire.
Institute of Technology Sligo - Dept of Computing
THE OSI MODEL
Application
Presentation
Session
Transport
Network
Data-Link
LAN Devices &
Technologies
The Data-Link &
Physical Layers
Physical
Table of Contents
Institute of Technology Sligo - Dept of Computing
Devices
What layer device?

What does it do?
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
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Connects LAN
segments;
Filters traffic based on
MAC addresses; and
Separates collision
domains based upon
MAC addresses.
Institute of Technology Sligo - Dept of Computing
Devices
What layer device?

What does it do?

Since it is a multi-port
bridge, it can also
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Connect LAN segments;
Filter traffic based on MAC
addresses; and
Separate collision
domains
However, switches also
offer full-duplex, dedicated
bandwidth to segments or
desktops.
Institute of Technology Sligo - Dept of Computing
Devices
What layer device?

What does it do?


Concentrates LAN
connections from
multiple devices into
one location
Repeats the signal (a
hub is a multi-port
repeater)
Institute of Technology Sligo - Dept of Computing
Devices
What layer device?

What does it do?




Interconnects networks and
provides broadcast control
Determines the path using
a routing protocol or static
route
Re-encapsulates the
packet in the appropriate
frame format and switches
it out the interface
Uses logical addressing
(i.e. IP addresses) to
determine the path
Institute of Technology Sligo - Dept of Computing
Media Types
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LAN Technologies
Three Most
Common Used
Today in
Networking
Institute of Technology Sligo - Dept of Computing
Ethernet/802.3
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Cable Specifications:
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10Base2
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10Base5
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Called Thicknet; uses coax
Max. distance = 500 meters
10BaseT
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
Called Thinnet; uses coax
Max. distance = 185 meters (almost 200)
Uses Twisted-pair
Max. distance = 100 meters
10 means 10 Mbps
Institute of Technology Sligo - Dept of Computing
Ethernet/802.3
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Ethernet is broadcast topology.

What does that mean?
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Every devices on the Ethernet segment sees every frame.
Frames are addressed with source and destination ______
addresses.
When a source does not know the destination or wants to
communicate with every device, it encapsulates the frame
with a broadcast MAC address: FFFF.FFFF.FFFF
What is the main network traffic problem caused by
Ethernet broadcast topologies?
Institute of Technology Sligo - Dept of Computing
Ethernet/802.3



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Ethernet topologies are also shared
media.
That means media access is controlled on
a “first come, first serve” basis.
This results in collisions between the data
of two simultaneously transmitting devices.
Collisions are resolved using what
method?
Institute of Technology Sligo - Dept of Computing
Ethernet/802.3


CSMA/CD (Carrier Sense Multiple Access with
Collision Detection)
Describe how CSMA/CD works:




A node needing to transmit listens for activity on the
media. If there is none, it transmits.
The node continue to listen. A collision is detected by
a spike in voltage (a bit can only be a 0 or a 1--it
cannot be a 2)
The node generates a jam signal to tell all devices to
stop transmitting for a random amount of time (backoff algorithm).
When media is clear of any transmissions, the node
can attempt to retransmit.
Institute of Technology Sligo - Dept of Computing
Address Resolution Protocol




In broadcast topologies, we need a way to
resolve unknown destination MAC addresses.
ARP is protocol where the sending device sends
out a broadcast ARP request which says,
“What’s you MAC address?”
If the destination exists on the same LAN
segment as the source, then the destination
replies with its MAC address.
However, if the destination and source are
separated by a router, the router will not forward
the broadcast (an important function of routers).
Instead the router replies with its own MAC
Institute of Technology Sligo - Dept of Computing
THE OSI MODEL
Application
Presentation
Transport Layer
Session
Transport
Network
A Quick Review
Data-Link
Physical
Table of Contents
Institute of Technology Sligo - Dept of Computing
Transport Layer Functions

Synchronization of the connection

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Flow Control


Three-way handshake
“Slow down, you’re overloading my memory buffer!!”
Reliability & Error Recovery


Windowing: “How much data can I send before
getting an acknowledgement?”
Retransmission of lost or unacknowledged segments
Institute of Technology Sligo - Dept of Computing
Transport’s Two Protocols

TCP



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

Transmission Control
Protocol
Connection-oriented
Acknowledgment &
Retransmission of
segments
Windowing
Applications:



Email
File Transfer
E-Commerce
UDP
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User Datagram
Protocol
Connectionless
No Acknowledgements
Applications:

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

Routing Protocols
Streaming Audio
Gaming
Video Conferencing
Institute of Technology Sligo - Dept of Computing
THE OSI MODEL
Application
Presentation
IP Addressing
Session
Transport
Network
Subnetting Review
Data-Link
Physical
Table of Contents
Institute of Technology Sligo - Dept of Computing
Logical Addressing

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
At the network layer, we use logical, hierarchical
addressing.
With Internet Protocol (IP), this address is a 32bit addressing scheme divided into four octets.
Do you remember the classes 1st octet’s value?
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Class A: 1 - 126
Class B: 128 - 191
Class C: 192 - 223
Class D: 224 - 239 (multicasting)
Class E: 240 - 255 (experimental)
Institute of Technology Sligo - Dept of Computing
Network vs. Host
Class A:
27 = 126 networks; 224 > 16 million hosts
N
Class B :
H
H
214 = 16,384 networks; 216 > 65,534 hosts
N
Class C :
H
N
H
H
221 > 2 million networks; 28 = 254 hosts
N
N
N
H
Institute of Technology Sligo - Dept of Computing
Why Subnet?



Remember: we are usually dealing with a
broadcast topology.
Can you imagine what the network traffic
overhead would be like on a network with 254
hosts trying to discover each others MAC
addresses?
Subnetting allows us to segment LANs into
logical broadcast domains called subnets,
thereby improving network performance.
Institute of Technology Sligo - Dept of Computing
Stealing Bits



In order to subnet, we must steal or “borrow” bits
from the host portion on the IP address.
First, we must to determine how many subnets
we need and how many hosts per subnet.
We do this through the power of 2

For example, I need 8 subnets from a Class C:



24 = 16 - 2 = 14 subnets
Remember: we subtract 2 because these subnets are not
used
How many host do we have?


It’s a Class C, so 4 bits are left: 24 = 16 - 2 = 14 hosts
Remember: we subtract 2 because one address is the
subnet address and one is the broadcast address
Institute of Technology Sligo - Dept of Computing
Subnet Mask


We determine the subnet mask by adding up the
decimal value of the bits we borrowed.
In the previous Class C example, we borrowed 4
bits. Below is the host octet showing the bits we
1
1and their
1 decimal
1
borrowed
values.
128 64 32 16
8
4
2
1
We add up the decimal value of these bits and get 240.
That’s the last non-zero octet of our subnet mask.
So our subnet mask is 255.255.255.240
Institute of Technology Sligo - Dept of Computing
Last Non-Zero Octet

Memorize this table. You should be able to:



Quickly calculate the last non-zero octet when given
the number of bits borrowed.
Determine the number of bits borrowed given the last
non-zero octet.
Determine the amount
of
bits left over for hosts and
Bits
Non-Zero
the number of Borrowed
host addresses
Octet available.
Hosts
2
3
4
5
6
192
224
240
248
252
62
30
14
6
2
Institute of Technology Sligo - Dept of Computing
CIDR Notation



Classless Interdomain Routing is a method of
representing an IP address and its subnet mask
with a prefix.
For example: 192.168.50.0/27
What do you think the 27 tells you?
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27 is the number of 1 bits in the subnet mask.
Therefore, 255.255.255.224
Also, you know 192 is a Class C, so we borrowed 3
bits!!
Finally, you know the magic number is 256 - 224 = 32,
so the first useable subnet address is 197.168.50.32!!
Let’s see the power of CIDR notation.
Institute of Technology Sligo - Dept of Computing
202.151.37.0/26

Subnet mask?
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
Bits borrowed?


256 - 192 = 64
First useable subnet address?

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Class C so 2 bits borrowed
Magic Number?


255.255.255.192
202.151.37.64
Third useable subnet address?

64 + 64 + 64 = 192, so 202.151.37.192
Institute of Technology Sligo - Dept of Computing
198.53.67.0/30

Subnet mask?


Bits borrowed?


256 - 252 = 4
Third useable subnet address?


Class C so 6 bits borrowed
Magic Number?


255.255.255.252
4 + 4 + 4 = 12, so 198.53.67.12
Second subnet’s broadcast address?

4 + 4 + 4 - 1 = 11, so 198.53.67.11
Institute of Technology Sligo - Dept of Computing
200.39.89.0/28

What kind of address is 200.39.89.32?





Class C, so 4 bits borrowed
Last non-zero octet is 240
Magic number is 256 - 240 = 16
32 is a multiple of 16 so 200.39.89.32 is a subnet
address--the second subnet address!!
What’s the broadcast address of 200.39.89.32?

32 + 16 -1 = 47, so 200.39.89.47
Institute of Technology Sligo - Dept of Computing
194.53.45.0/29

What kind of address is 194.53.45.26?






Class C, so 5 bits borrowed
Last non-zero octet is 248
Magic number is 256 - 248 = 8
Subnets are .8, .16, .24, .32, ect.
So 194.53.45.26 belongs to the third subnet address
(194.53.45.24) and is a host address.
What broadcast address would this host use to
communicate with other devices on the same
subnet?

It belongs to .24 and the next is .32, so 1 less is .31
(194.53.45.31)
Institute of Technology Sligo - Dept of Computing
No Worksheet Needed!




After some practice, you should never need a
subnetting worksheet again.
The only information you need is the IP address
and the CIDR notation.
For example, the address 221.39.50/26
You can quickly determine that the first subnet
address is 221.39.50.64. How?



Class C, 2 bits borrowed
256 - 192 = 64, so 221.39.50.64
For the rest of the addresses, just do multiples of
64 (.64, .128, .192).
Institute of Technology Sligo - Dept of Computing
The Key!!

MEMORIZE THIS TABLE!!!
Bits
Non-Zero
Borrowed Octet
Hosts
2
192
62
3
224
30
4
240
14
5
248
6
6
252
2
Institute of Technology Sligo - Dept of Computing
Practice On Your Own

Below are some practice problems. Take out a
sheet of paper and calculate...



1.
2.
3.
4.
5.
6.
Bits borrowed
Last non-zero octet
Second subnet address and broadcast address
192.168.15.0/26
220.75.32.0/30
200.39.79.0/29
195.50.120.0/27
202.139.67.0/28
Challenge: 132.59.0.0/19
Answers