Networking - OSI and IPv4

Source to Destination Delivery

Source to Destination Delivery

What is the Open Systems Interconnection (OSI) Model?

• OSI model describes seven layers that computer systems use to communicate over a network.
• Introduce in 1983 by US DoD and adopted by the ISO standards in 1984​

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The Seven Layers of the Open Systems Interconnection Model

Layer-7: Application Layer

• This is the layer that most users interact with and will recognise.

• Provides network services to the end user. ​

• These services are protocols that work with the data the client is using. HTTP, HTTPS etc that is used with web browsers such as Google Chrome, Firefox, and Internet Explorer.​

• Other examples of applications that use this layer are Office, Outlook, and Skype.​

Layer-6: Presentation Layer

• Syntax processing or converting data from one format to another.​

• This layer handles translating the data from the top layer, which is presented in application format, to network format and vice versa.​

• After the Presentation layer processes the data from one format to another, the information is then passed to the Session layer or the Application layer depending on whether the data is transmitting or receiving​

Layer-5: Session Layer

• The construction, direction, and conclusion of connections between devices occur. ​

• This layer supports multiple types of connections as well as being responsible for authentication and reconnection if a network interruption should occur.​

• After the session is established the data then passes to or from the Transport layer​

Layers-4: Transport Layer

• Transmission of data across network connections​

• Coordinates how much data to send, how fast, where it goes, and these sort of things. ​

• Services may be provided by TCP and “User Datagram Protocol” or UDP. Other protocols may provide additional capabilities including error recovery, data flow, and retransmission.​

Layer-3: Network Layer

• Handles the routing of data​

• Each frame of data is examined to conclude if the data has reached its ultimate target. ​

• Sends data to the correct destination on transmitted and received transmissions ​

• The IP portion of Transmission Control Protocol /Internet Protocol (TCP/IP) is the commonly known network layer for the Internet.​

Layer-2: Data Link

• Establishes and terminates a connections ​

• Frames ​

• Logical Link Control (LLC), which identifies ​network protocols, performs error checking and synchronizes frames​

• Media Access Control (MAC) which uses ​MAC addresses to connect devices and ​
  define permissions to transmit and receive data.​

Layers-1: Physical

• Physical cable between network nodes​

• Wireless connection between network nodes ​

• Connector, the ​electrical cable or ​wireless technology ​

• Transmission of the raw data packets ​0s and 1s,​

• Control of bit rate​

• Electrons, RF or Light​

Advantages of the OSI Model

The OSI model helps users and operators of computer networks:​

• Determine the required hardware and software to build their network​

• Understand and communicate the process followed by components communicating across a network​

• Perform troubleshooting, by identifying which network layer is causing an issue and focusing efforts on that layer​

Advantages of the OSI Model

The OSI model helps network device manufacturers and networking software vendors:​

• Create devices and software that can communicate with products from any other vendor, allowing open interoperability​

• Define which parts of the network their products should work with.​

• Communicate to users at which network layers their product operates – for example, only at the application layer, or across the stack.

OSI In Action Example 1

OSI In Action Example 2

TCP/IP Layer Stack Model

TCP/IP vs OSI

• The main difference is that OSI is a conceptual model that is not practically used for communication. Rather, it defines how applications can communicate over a network. ​

• TCP/IP, on the other hand, is widely used to establish links and network interaction.​

• The TCP/IP protocols lay out standards on which the internet was created, ​

• While the OSI model provides guidelines on how communication has to be done. Therefore, TCP/IP is a more practical model​

Operation Examples Using Both Models

Computer Networks

1. LAN (Local Area Network)

2. WAN (Wide Area Network)

What is the Internet Protocol

The Internet Protocol (IP) is the addressing scheme for machine on a network or the internet. The IP address per machine must be unique in the network it is connected to. ​

IPV1, IPV2 and IPV3 where experimental in 1973 to 1978.​

In 1981 the IPV4 protocol was established, which means that the addressing scheme is almost 40 years old. ​

192.168.1.20​

10.0.0.1​

68.32.240.1​

IPv4

Human readable dotted decimal format

Machine readable dotted binary format, each number is an octet because there are 8 binary digits, just like a byte. ​

Therefore 4 x 8 = 32​

IPv4 Possible Combinations of Addressess

Remember there are 32 binary positions.

Possible addressess

• First address:
• Last address

IPv4 Classes

IPv4 Formatting

Class D - A multicast (one-to-many) is different from a broadcast (one-to-al). Every device on a logical network must process a broadcast, whereas only devices configured to listen for a Class D address receive a multicast.

Class E - Class E addresses are reserved for experimental purposes and should not be used to address hosts or multicast groups.

Loopback Address

IP address range 127.0.0.0 to 127.255.255.255 is reserved.​

This is for the loopback address network and local host.​
​

• Allows for a device to send and receive its own data packet​

• Allows for analysis like testing and debugging, or allowing routers to communicate in specific ways​

$ cat /etc/hosts

127.0.0.1 localhost
::1 localhost
127.0.0.2 vakare
::1 vakare

IPv4 Addressing

What is this class is this address and its dotted decimal notation:​

Netmask/CIDR

• Netmasks defines how large a network can be, this help limit the number of devices that can connect to your network. i.e., the number of the available address

• Can help distinguish between network and host within the IP address.

• Classless Inter-Domain Routing (CIDR)/Netmask was designed by the Internet Engineering Task Force (IETF) to slow down the exhaustion of addresses and chaotic routing tables.​

• CIDR (e.g., /32)is the number of the bit from the left

• Size of Subnet Mask it's 32 bits

Examples

Netmask - Subnetting

So lets look at the binary subnet mask, we can see that /## denotes the number of ones masked off which means only the addresses not masked are available to that network. ​

Calculating the CIDR

The IP addresses range is from 21.19.35.64 and 21.19.35.127. Find the CIDR block?​

CIDR block is 21.19.35.64/26

Netmask - Subnetting

So lets look at the binary subnet mask, we can see that /## denotes the number of ones masked off which means only the addresses not masked are available to that network. ​

Network Address (Start Address)

• It is the address used to identify a specific network. It represents the beginning of a range of IP addresses assigned to devices (hosts) within that network.

• The network address is obtained by performing a logical AND operation between an IP address and its corresponding subnet mask.

• This operation effectively "masks out" the host portion of the IP address, leaving only the network portion intact

• All host bits are 0

Example

IP Address: 192.168.1.100
Subnet Mask: 255.255.255.0

1. Convert IP Address to Binary: IP=11000000.10101000.00000001.01100100

2. Convert Subnet Mask to Binary: SNM= 11111111.11111111.11111111.00000000

3. Perform Logical AND Operation:

4. Network Address: 192.168.1.0

Broadcast Address (Final Address):

The broadcast address is used to send data packets to all devices within a specific network. It represents the end of the range of IP addresses assigned to devices within that network

Example

1. Invert Subnet Mask to get Wildcard Mask: 00000000.00000000.00000000.11111111

2. Perform Logical OR Operation:

OR

=

Broadcast Address: 192.168.1.255