Fundamentals of computer Networks

The first chapter:

Network must first have many computers, to realize the sharing of resources and delivery of information

Computer network consists of several hosts, a communication subnet, and a lot of communication protocols, communication subnets are network nodes and communication links, responsible for data transmission and exchange

The transmission mode of computer network is broadcast network and point-point Network

There are three types of broadcast networks:

Unicast: Sends data to all destination nodes of the network in one-to-a-send format.

Multicast: Send data to a group of hosts on the network in a pair of send forms.

Broadcast: Send data to all destination nodes on the network in a pair of all send forms.

Point-to-point network:

The communication mode between the two nodes is point-to-point. If there is no direct connection between the two computers, then the packet transfer between them through the intermediate nodes receive, store, forward, until the destination node.

Chapter II:

Devices needed to connect to the network

1. Network card, inserted in the computer or server expansion slot, through network lines (such as twisted pair, coaxial cable or optical fiber) and network Exchange data, share resources

There are two main functions of the network card, one is to encapsulate the data of the computer, and send the data to the network via the network cable, and the second is to receive the data uploaded by the Internet, and then to the computer.

Network card Although there are many, not enough one thing in common is that each NIC has a unique ID number, also known as the MAC address (48-bit), MAC address is burned in the Rom on the NIC, like each of our genetic DNA, even in the world will never repeat.

2. Hubs, mainly used to form a network of star topology. In a network, a hub is a centralized point that connects computers in a network through a multitude of ports, enabling different computers to communicate with each other.

The basic function of a hub is information distribution, which forwards a signal received by one port to all other ports. At the same time, all ports of the hub share the bandwidth of the hub. When we connect only one computer to a 10mb/s-bandwidth hub, the bandwidth of this computer is 10mb/s, and when we connect two computers, the bandwidth of each computer is 5mb/s, and when you connect 10 computers, the bandwidth is 1mb/s. When you use hub networking, the more computers you connect, the slower your network speed

3. Switch, also used to form a network of star topology. In appearance, switches are almost the same as hubs, and their ports are almost the same as those for connections and hubs, but because the switch uses switching technology, its performance is better than the hub

The switch uses the switching technology, which can communicate in parallel instead of distributing bandwidth evenly like a hub. Each of the ports on a single-MB/s switch is 100mb/s, each connected computer communicates at a 100mb/s rate, rather than distributing bandwidth evenly as the hub does, which enables the switch to provide better communication performance.

Supplemental: Mac (Media Access Control) addresses, or MAC address, hardware location, are used to define the locations of network devices. In the OSI model, the third layer of the network layer is responsible for the IP address, and the second layer of the data link is responsible for MAC addresses. Therefore, a host will have an IP address, and each network location will have a Mac URL dedicated to it

4. Routers, which are devices that work on the network layer, are mainly used for interconnection of different types of networks.

The functions of routers are mainly embodied in the following aspects. Routing function: the so-called routing, that is, the choice of information transmission path. When we use routers to connect different networks, routers can choose the best information transfer path between different networks, allowing information to be transferred to their destination more quickly. In fact, the Internet we visit is through a number of routers to connect different networks around the world, routers in the Internet to select the path and forwarding information, so that the world's network can share network resources

5. Modem

function is the computer to represent the digital signal in the analog telephone line transmission, so as to achieve the purpose of data communications, mainly by two parts of the function: modulation and reconciliation. Modulation is the conversion of a digital signal to an analog signal suitable for transmission on the telephone line, the demodulation is to convert the analog signal on the telephone line into a digital signal, received by the computer and processed

TCP/IP Detailed

An IP address is a 32-bit binary number that identifies a computer in the network.

IP addresses are typically expressed in two ways: binary and decimal.
Binary number means: Inside the computer, the IP address is represented by a 32-bit binary number, each 8 bits is a paragraph, a total of 4 paragraphs. such as 10000011.01101011.00010000.11001000.
Decimal number: For ease of use, each segment is usually converted to a decimal number. such as the 10000011.01101011.00010000.11001000 converted format is:
130.107.16.200. This format is the format of the IP address that we configured in the computer.

3, the composition of IP address
The IP address consists of two parts: the network ID and the host ID.
Network ID: Used to identify the network in which the computer is located, or it can be said to be the number of the network.

Host ID: Used to identify different computers within the network, that is, the number of the computer.

IP Address provisions:
The network number cannot start with 127, the first byte cannot be all 0, and it cannot be all L. The host number cannot be all 0, nor can it be all l

4. Classification of IP addresses
Because IP addresses are limited resources, to better manage and use IP addresses, InterNIC divides IP addresses into 5 classes (ABCDE) based on the size of the network:
Class A address: The first group number (the Top 8) represents the network number, and the highest level is 0, so that only 7 bits can represent the network number, can be represented by the network number has 27-2=126 (remove the full "0" and the full "1" two addresses), the scope is: 1.0.0.0~126.0.0.0. The latter three groups (24-bit) represent the host number, the number of host numbers that can be represented is 224-2 = 16,777,214, that is, a class of network can accommodate 16777214 hosts. Class A addresses are assigned only to very large networks. Class B Address: The first two groups (the first 16 digits) represent the network number, and the latter two groups (16 bits) represent the host number. And the highest level is 10, the network number can be expressed as 214 = 16,384, the range is: 128.0.0.0~191.255.0.0. The number of hosts that a Class B network can hold is 216-2=65534. Class B IP addresses are typically used for medium-sized networks.
Class C Address: The first three groups represents the network number, the last group number represents the host number, and the highest level is 110, the maximum number of networks is 221=2097152, the range is: 192.0.0.0~223.255.255.0, can accommodate the number of hosts 28-2=254 host. Class C IP addresses are typically used for small networks. Class D Address: The highest bit is 1110, which is the multicast address. Class E Address: The highest bit is 11110, reserved for future use.
Note: You can only configure computers A, B, and C three IP addresses in the network, not the Class D, class E two addresses. 5. Several special IP addresses
Host number 0: Indicates the network number and cannot be assigned to the host. such as: 192.168.4.0 is the network address.
Host Number 1: Indicates that a broadcast is being sent to the specified subnet. Such as: 192.168.1.255 indicates to the network number 192.168.1.0 broadcast.
255.255.255.255: Broadcast address in the network. 127.X.Y.Z: Test address, cannot be configured to computer

5. Subnet mask

When we configure the ICP/IP parameter, we configure the subnet mask in addition to configuring the IP address. The subnet mask is also a 32-bit binary number, the configuration is: the IP address network bit corresponding subnet mask is set to "1", the host bit corresponding subnet mask is set to "0", such as: For the IP address is 131.107.16.200 host, because it is a Class B address, the first two groups of network number, the latter two groups are the host number. The subnet mask is configured as:
11111111.11111111.00000000.00000000, converted to a decimal number of: 255.255.0.0. Thus, the default subnet mask for each type of address is:

Class A: 11111111.00000000.0000000.00000000 or 255.0.0.0

Class B: 11111111.11111111.00000000.00000000 or 255.255.0.0

Class C: 11111111.11111111.11111111.00000000 is 255.255.255.0

The reason is to configure the subnet mask, because in the Internet, each host IP address is composed of network address and host address two parts, in order to enable the computer automatically from the IP address to isolate the corresponding network address, you need to specifically define a network mask, also known as the subnet mask, This allows you to quickly determine which part of the IP address represents the network number, which part represents the host number, and whether the two IP addresses belong to the same network.

6. Default Gateway

In the Internet, a gateway is an intermediary device that connects the intranet to other networks on the Internet, and the gateway address can be understood as the channel address for intranet and Internet Information transmission

7. DNS for Domain name addresses

It consists of a parser and a domain name server. A domain name server is a domain name and corresponding IP address that holds all the hosts in the network, and a server that converts the domain name to the IP address feature. Where the domain name must correspond to an IP address, and the IP address does not necessarily have a domain name.

Fundamentals of computer Networks