1. Semester 3 Chapter 1
Review

2. Table of Contents Review the OSI Model LAN Devices & Technologies
IP Addressing
CIDR Notation
Routing
Transport Layer

3. Open Systems Interconnected Reference Model
Review The Model
Open Systems Interconnected Reference Model

4. Why A Layered Model? Reduces complexity Standardizes interfaces
Facilitates modular engineering
Ensures interoperable technology
Accelerates evolution
Simplifies teaching & learning
Application
Presentation
Session
Transport
Network
Data-Link
Physical

5. Application Layer
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.
Application
Presentation
Session
Transport
Network
Data-Link
Physical

6. Presentation Layer 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.
Application
Presentation
Session
Transport
Network
Data-Link
Physical

7. Session Layer
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
Application
Presentation
Session
Transport
Network
Data-Link
Physical

8. Transport Layer
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 not acknowledge the receipt of packets.
Application
Presentation
Session
Transport
Network
Data-Link
Physical

9. Network Layer
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
Application
Presentation
Session
Transport
Network
Data-Link
Physical

10. Data-Link Layer Provides access to the media
Handles error notification, network topology issues, and physically addressing the frame.
Media Access Control through either...
Deterministic—token passing
Non-deterministic—broadcast topology (collision domains)
Important concept: CSMA/CD
Application
Presentation
Session
Transport
Network
Data-Link
Physical

11. Physical Layer
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
Application
Presentation
Session
Transport
Network
Data-Link
Physical

12. 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
Presentation
Data
Session
Data
Transport
Segments
Network
Packets
Data-Link
Frames
Physical
Bits

13. Encapsulation Example
You type an 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.
Application
Presentation
Session
Transport
Network
Data-Link
Physical

14. Encapsulation Example
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.
Application
Presentation
Session
Transport
Network
Data-Link
Physical

15. LAN Devices & Technologies
The Data-Link & Physical Layers
Data-Link
Physical

16. Devices What does it do? What layer device? Connects LAN segments;
Filters traffic based on MAC addresses; and
Separates collision domains based upon MAC addresses.

17. Devices What layer device? What does it do?
Since it is a multi-port bridge, it can also
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.

18. Devices What does it do? What layer device?
Concentrates LAN connections from multiple devices into one location
Repeats the signal (a hub is a multi-port repeater)

19. 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

20. Media Types

21. Three Most Common Used Today in Networking
LAN Technologies
Three Most Common Used Today in Networking

22. Ethernet/802.3 Cable Specifications: 10Base2 10Base5 10BaseT
Called Thinnet; uses coax
Max. distance = 185 meters (almost 200)
10Base5
Called Thicknet; uses coax
Max. distance = 500 meters
10BaseT
Uses Twisted-pair
Max. distance = 100 meters
10 means 10 Mbps

23. Ethernet/802.3 Ethernet is broadcast topology. What does that mean?
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?

24. Ethernet/802.3 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?

25. 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 continues 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 (back-off algorithm).
When media is clear of any transmissions, the node can attempt to retransmit.

26. 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 address.

27. IP Addressing
Subnetting Review
Network

28. Logical Addressing
At the network layer, we use logical, hierarchical addressing.
With Internet Protocol (IP), this address is a 32-bit addressing scheme divided into four octets.
Do you remember the classes 1st octet’s value?
Class A:
Class B:
Class C:
Class D: (multicasting)
Class E: (experimental)

29. Network vs. Host
Class A: 27 = 126 networks; 224 > 16 million hosts N H
Class B : 214 = 16,384 networks; 216 > 65,534 hosts N H
Class C : 221 > 2 million networks; 28 = 254 hosts N H

30. 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.

31. Four Subnetting Steps
To correctly subnet a given network address into subnet addresses, ask yourself the following questions:
How many bits do I need to borrow?
What’s the subnet mask?
What’s the “magic number” or multiplier?
What are the first three subnetwork addresses?
Let’s look at each of these questions in detail

32. 1. How many bits to borrow?
First, you need to know how many bits you have to work with.
Second, you must know either how many subnets you need or how many hosts per subnet you need.
Finally, you need to figure out the number of bits to borrow.

33. 1. How many bits to borrow? How many bits do I have to work with?
Depends on the class of your network address.
Class C: 8 host bits
Class B: 16 host bits
Class A: 24 host bits
Remember: you must borrow at least 2 bits for subnets and leave at least 2 bits for host addresses.
2 bits borrowed allows = 2 subnets

34. 1. How many bits to borrow? I need x hosts:
How many subnets or hosts do I need?
A simple formula:
Total Bits = Bits Borrowed + Bits Left
TB = BB + BL
I need x subnets:
I need x hosts:
Remember: we need to subtract two to provide for the subnetwork and broadcast addresses.

35. 1. How many bits to borrow? Class C Example: 210.93.45.0
Design goals specify at least 5 subnets so how many bits do we borrow?
How many bits in the host portion do we have to work with (TB)?
What’s the BB in our TB = BB + BL formula? (8 = BB + BL)
2 to the what power will give us at least 5 subnets?
= 6 subnets

36. 1. How many bits to borrow? How many bits are left for hosts?
TB = BB + BL
8 = 3 + BL
BL = 5
So how many hosts can we assign to each subnet?
= 30 hosts

37. 1. How many bits to borrow? Class B Example: 185.75.0.0
Design goals specify no more than 126 hosts per subnet, so how many bits do we need to leave (BL)?
How many bits in the host portion do we have to work with (TB)?
What’s the BL in our TB = BB + BL formula? (16 = BB + BL)
2 to the what power will insure no more than 126 hosts per subnet and give us the most subnets?
= 126 hosts

38. 1. How many bits to borrow? How many bits are left for subnets?
TB = BB + BL
16 = BB + 7
BL = 9
So how many subnets can we have?
= 510 subnets

39. 2. What’s the 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 3 bits. Below is the host octet showing the bits we borrowed and their decimal values. 1
We add up the decimal value of these bits and get That’s the last non-zero octet of our subnet mask.
So our subnet mask is

40. 3. What’s the “magic number?”
To find the “magic number” or the multiplier we will use to determine the subnetwork addresses, we subtract the last non-zero octet from 256.
In our Class C example, our subnet mask was is our last non-zero octet.
Our magic number is = 32

41. 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 the number of host addresses available.

42. 4. What are the subnets?
We now take our “magic number” and use it as a multiplier.
Our Class C address was
We borrowed bits in the fourth octet, so that’s where our multiplier occurs
1st subnet:
2nd subnet:
3rd subnet:
We keep adding 32 in the fourth octet to get all six available subnet addresses.

43. Host & Broadcast Addresses
Now you can see why we subtract 2 when determining the number of host address.
Let’s look at our 1st subnet:
What is the total range of addresses up to our next subnet, ?
to or 32 addresses
.32 cannot be assigned to a host. Why?
.63 cannot be assigned to a host. Why?
So our host addresses are or 30 host addresses--just like we figured out earlier.

44. A Different Way to Represent a Subnet Mask
CIDR Notation
A Different Way to Represent a Subnet Mask
Network

45. CIDR Notation
Classless Interdomain Routing is a method of representing an IP address and its subnet mask with a prefix.
For example: /27
What do you think the 27 tells you?
27 is the number of 1 bits in the subnet mask. Therefore,
Also, you know 192 is a Class C, so we borrowed 3 bits!!
Finally, you know the magic number is = 32, so the first useable subnet address is !!
Let’s see the power of CIDR notation.

46. 202.151.37.0/26 Subnet mask? Bits borrowed? Magic Number?
Bits borrowed?
Class C so 2 bits borrowed
Magic Number?
= 64
First useable subnet address?
Third useable subnet address?
= 192, so

47. 198.53.67.0/30 Subnet mask? Bits borrowed? Magic Number?
Bits borrowed?
Class C so 6 bits borrowed
Magic Number?
= 4
Third useable subnet address?
= 12, so
Second subnet’s broadcast address?
= 11, so

48. 200.39.89.0/28 What kind of address is 200.39.89.0?
Class C, so 4 bits borrowed
Last non-zero octet is 240
Magic number is = 16
32 is a multiple of 16 so is a subnet address--the second subnet address!!
What’s the broadcast address of ?
= 47, so

49. 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 = 8
Subnets are .8, .16, .24, .32, ect.
So belongs to the third subnet address ( ) 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 ( )

50. 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 /26
You can quickly determine that the first subnet address is How?
Class C, 2 bits borrowed
= 64, so
For the rest of the addresses, just do multiples of 64 (.64, .128, .192).

51. The Key!!
MEMORIZE THIS TABLE!!!

52. Practice On Your Own
Below are some practice problems. Take out a sheet of paper and calculate...
Bits borrowed
Last non-zero octet
Second subnet address and broadcast address
/26
/30
/29
/27
/28
Challenge: /19
Challenge: /16
Answers

53. Answers Don’t Cheat Yourself!!
Work them out before you check your answers. Click the back button if you’re not done. Otherwise, click anywhere else in the screen to see the answers.

54. Path Determination & Packet Switching
Routing Basics
Path Determination & Packet Switching
Network

55. A Router’s Functions
A router is responsible for determining the packet’s path and switching the packet out the correct port.
A router does this in five steps:
De-encapsulates the packet
Performs the ANDing operation
Looks for entry in routing table
Re-encapsulates packet into a frame
Switches the packet out the correct interface

56. Routed v. Routing Protocols
What is a routed protocol?
Routed protocols are protocols that enable data to be transmitted across a collection of networks or internetworks using a hierarchical addressing scheme.
Examples include IP, IPX and AppleTalk.
A routable protocol provides both a network and node number to each device on the network. Routers AND the address to discover the network portion of the address.
An example of a protocol that is not routable is NetBEUI because it does not have a network/node structure.

57. Routed v. Routing Protocols
What is a routing protocol?
A routing protocol is a protocol that determines the path a routed protocol will follow to its destination.
Routers use routing protocols to create a map of the network. These maps allow path determination and packet switching. Maps become part of the router’s routing table.
Examples of routing protocols include: RIP, IGRP, EIGRP, & OSPF

58. Multi-protocol Routing
Routers are capable of running multiple routing protocols (RIP, IGRP, OSPF, etc.) as well as running multiple routed protocols (IP, IPX, AppleTalk).
For a router to be able use different routing and routing protocols, you must enable the protocols using the appropriate commands.

59. Dynamic v. Static Routing
Dynamic routing refers to the process of allowing the router to determine the path to the destination.
Routing protocols enable dynamic routing where multiple paths to the same destination exist.

60. Dynamic v. Static Routing
Static routing means that the network administrator directly assigns the path router are to take to the destination.
Static routing is most often used with stub networks where only one path exists to the destination.

61. Default Routes
A default route is usually to a border or gateway router that all routers on a network can send packets to if they do not know the route for a particular network.

62. Routing Protocol Classes
Routing protocols can be divided into three classes:
Distance–vector: determines the route based on the direction (vector) and distance to the destination
Link-state: opens the shortest path first to the destination by recreating an exact topology of the network in its routing table
Hybrid: combines aspects of both

63. Convergence
Convergence means that all routers share the same information about the network. In other words, each router knows its neighbor routers routing table
Every time there is a topology change, routing protocols update the routers until the network is said to have converged again.
The time of convergence varies depending upon the routing protocol being used.

64. Distance-vector Routing
Each router receives a routing table periodically from its directly connected neighboring routers.
For example, in the graphic, Router B receives information from Router A. Router B adds a distance-vector number (such as a number of hops), and then passes this new routing table to its other neighbor, Router C.

65. Link-state Routing
Link-state protocols maintain complex databases that summarize routes to the entire network.
Each time a new route is added or a route goes down, each router receives a message and then recalculates a spanning tree algorithm and updates its topology database.

66. Comparing the Two DISTANCE-VECTOR LINK-STATE
Views network topology from neighbor’s perspective
Gets common view of entire network topology
Adds distance vectors from router to router
Calculates the shortest path to other routers
Frequent, periodic updates: slow convergence
Event triggered updates: fast convergence
Passes copies of routing tables to neighbors
Passes link-state routing updates to all routers in the system.

67. Hybrid Routing
Cisco’s proprietary routing protocol, EIGRP, is considered a hybrid.
EIGRP uses distance-vector metrics. However, it uses event-triggered topology changes instead of periodic passing of routing tables.

68. Transport Layer
Transport
A Quick Review

69. Transport Layer Functions
Synchronization of the connection
Three-way handshake
Flow Control
“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

70. Transport’s Two Protocols
TCP
Transmission Control Protocol
Connection-oriented
Acknowledgment & Retransmission of segments
Windowing
Applications:
File Transfer
E-Commerce
UDP
User Datagram Protocol
Connectionless
No Acknowledgements
Applications:
Routing Protocols
Streaming Audio
Gaming
Video Conferencing