Computer Networking is the subject which explains how computers connect with each other for sharing resource and information and what technologies and devices they use for the coonectivity.
- Medium ( How are you connected? )
- Addressing ( How do you locate and identify the other party? )
- Content ( What information are sharing with the other party? )
Uniquely identify device on a network
- 32-bit address
- 192.168.112.20
The range of all possible IPv4 addresses was originally segmented into five classes, A through E. A, B, and C were used for general unicast assignments, class D was designated for multicast addressing, and class E was set aside for "experimental" use.
Here's a visualization of the entire IPv4 address space. Each square represents one possible value of the first octet of an address. For instance, the square on the top right, labeled 15, represents all the IPv4 addresses that start with 15 as their first octet (e.g. 15.72.9.277).
Visualization of the IPv4 address space. Each square represents the first octet of an IPv4 network address.
- The pink squares (0, 10, and 127) are blocks that are entirely reserved.
- The blue squares are blocks that are partially reserved. For instance, not all of the 192 block is reserved, but some of it is.
- The entire green row (starting at 224) is set aside for IP multicast
- And the entire orange bottom row (starting at 240) was originally set aside for "future use" but was effectively lost due to being blocked as invalid.
- RFC 6890 - Special-Purpose IP Address Registries, April 2013
- RFC 1918 - Address Allocation for Private Internets, February 1996
- Learn more about Wikipedia - IPv4 Address Exhaustion
Question : How many individual addresses are there on a /22 network? 2^10 - 3 = 1021 addresses 192.168.112.10/22 (Classless Interdomain Routing )(CIDR)
Conversion : IP Address to Binary
Question: IP addresses are on the same subnet as 122.48.253.2/18? 122.58.200.200 , 122.48.193.61
Question: Write an IP address that is in same subnet as 172.254.3.17/8? All IP address between 172.0.0.0 - 172.254.3.17 are is in same subnet.
If you recall, the number of addresses that are available for use in a netblock were reduced by three, because those three addresses are reserved for something. Well, what are they?
- The first address (.0) is used for identification of the network,
- The follow address (.1) is often assigned to the router,
- The last address (.255) is called the broadcast address. Anything sent to the broadcast address will be sent out to all devices on the network.
Some basic reading on subnetworks and Classless Inter-Domain Routing (CIDR):
- Subnetworks,
- A good read on CIDR with a helpful table on all IPv4 CIDR blocks.
And several technical reports on the following subjects:
The OSI model is a breakdown of the various aspects of network communication. It is concerned with the ability of different systems to be connected with each other. It's a conceptual breakdown of all the parts that are involved and groups them into logical sections. Let's check them out.
There are 7 layers in the OSI model. We'll start at the top-most layer, layer 7, and work our way down to layer 1.
Layer 7 - Application
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical
Remember that the OSI model is a conceptual model of how network communication occurs. For network communication to happen, the layers must work together to transmit a message from one device to another.
( People Do Not Throw Sausage Pizza Away )
The OSI model is a conceptual model and helps describe data in many ways. It provides a standard for how network communication occurs, how data is transferred, and provides a way to group similar protocols together.
For example, network devices can be grouped at several different layers in the OSI model. Layer 1 of the OSI model deals with the physical and electrical specification for devices. Items such as physical cables, wireless signless, the network identification card (NIC) inside a computer are all grouped at the Layer 1 level. But even though Layer 1 is called the physical layer, that doesn't mean that every physical device shows up there. For example, a switch is a Layer 2 device and a router is a Layer 3 device.
The OSI Model also helps group network protocols together. Here are some of the most common protocols at each layer:
Layer 7 = HTTP
Layer 6 = SSL and TLS
Layer 5 = socket
Layer 4 = TCP and UDP
Layer 3 = IP and ICMP
Layer 2 = ARP
Layer 1 = 1000BASE-T, DSL, DOCSIS, 802.11a/b/g/n
In the OSI model, a layer is only concerned with the layers above and below it. For example, layer 3 (the Network layer) is only concerned with the two layers that are on either side of it:
Layer 4 - the Transport layer
Layer 2 - the Data Link layer
Layer 3 will receive data from Layer 4 and send it to Layer 2 or it will receive data from Layer 2 and send it to Layer 4.
Layer 7 (the Application layer) is at the very top of the OSI model. Since it is at the top, it is only concerned with sending data to Layer 6 (the Presentation layer) or receiving data from Layer 6.
A single layer does not need to know the whole path that data takes through the OSI model. It just need to know about the layers above and below it that it needs to interact with. Now, why is this important? Each layer in the OSI model is an abstraction layer. An abstraction layer is:
a way of hiding the working details of a subsystem
For example, the way that the data is formatted, processed, and changed in Layer 2 does not matter to Layer 4, because Layer 3 abstracts those implementation details away. All Layer 4 has to worry about is how it needs to receive data from Layer 3 - it doesn't have to worry about the specifics of Layer 2 (since that's Layer 3's job).
Earlier, I said:
Layer 3 will receive data from Layer 4 and send it to Layer 2 or it will receive data from Layer 2 and send it to Layer 4.
When does data move down the layers from Layer 4 to Layer 3 to Layer 2 and when does the data move up the layers from Layer 2 to Layer 3 to Layer 4? These two processes are called encapsulation and decapsulation. Let's take a look at them in more detail.
Remember that the OSI model is a conceptual model of how data is packaged and sent across a network to another device. In this scenario, let's assume that there are only two devices that are trying to communicate with each other. The OSI model is used on both devices.
As the data is being packaged up on a sending device, the data moves down the OSI model; this process of the data moving down the OSI model is called encapsulation.
When the data is being unpacked on a receiving device, the data moves up OSI model; this process of the data moving up the OSI model is called decapsulation.
To recap, when data travels down the OSI model, the data from a higher layer becomes the "payload" for a lower layer. When the data moves from a higher layer to a lower layer, the data is wrapped in new information called a "header" and a "footer". This is where it gets the name "encapsulation"; because the data is wrapped (or encapsulated) with new header/footer layers.
Conversely, the opposite happens when traveling up the OSI model. As the data moves up the OSI model, these header/footer layers are removed. This is where it gets the name "decapsulation".
A network switch is a multiport network bridge that uses media access control addresses(MAC) to forward data at the data link layer (layer 2) of the OSI model. Some switches can also forward data at the network layer (layer 3) by additionally incorporating routing functionality. Such switches are commonly known as layer-3 switches or multilayer switches.
Unicast 1:1 Multicast 1:Many Broadcast 1:All
A Fully Qualified Domain Name (FQDN) consists of three parts - the hostname, domain, and top-level domain (TLD). The format looks like so,
[host name].[domain].[tld]
For the FQDN www.github.com - www is the hostname, github is the domain, and com is the top-level domain.
Other examples of FQDNs include:
- www.wikipedia.org
- www.baidu.com
- maps.google.com
- news.yandex.ru
