The network layer protocol of the network layer, why does the protocol structure of the LAN not incl

Why does the protocol structure of the LAN not include the network layer, the process of network access is actually a process of finding the way by checking the map. 1.One layer mainly refers to physical transmission, which involves mutual access, so it is impossible not to have a layer, in other words, how can you communicate with others without physical transmission?

Even if it is wireless, it is also called transmission, but the transmission medium is not our ordinary light and electricity) 2What is a narrow sense of LAN, LAN refers to the collection of all devices in the same IP network segment. 3.

Layer 3 mainly refers to routing, that is, the process of finding routes, and routes are only used if the IP addresses belong to different network segments. When you access a host in a different network segment, he will first find the gateway, that is, the router (equivalent to when we hit **, if you dial the external line, you need to go to the telecommunications bureau first), and then find the routing table through the router (that is, check the map) to determine which way your blanking spring breath should be sent out. 4.

Why does LAN only involve the physical layer and the link layer? 1) It involves the physical layer, which needs no more explanation2) It does not involve the network layer (layer 3), because the network layer only serves the IPs of different network segments 3) For the access to the local area network, because it belongs to the same network segment (that is, all computers are eventually connected to the same interface of the router), there is no need to find a map. Here's an example:

You live in a dormitory, you want to find a friend who lives in the same building and you don't know, you just need to shout: I am Xiao A, who is Xiao C, everyone will hear it, and then Xiao C will agree, you know each other's location, and you don't need to go through the trouble to check the map. - This is the interview on the second floor, and the process of getting to know each other one by one is the process of ARP parsing that is called upstairs, that is, determining the location of the other party.

In fact, even if it is access within the LAN, it also needs to involve three layers or more, for example: you and the computer in the LAN FTP file transmission, in fact, FTP is a seven-layer service, you want to send a message, you need to encapsulate the message into 7 layers, and then layer, after receiving the other party, you also have to unpack the package layer by layer. So, to be precise, it should be described like this:

The protocols at the network layer include IP, IPX, RIP, and OSPF. It is the most complex layer of the OSI reference model and the highest layer of the communication subnet, which provides services to the resource subnet on top of the next two layers. The main task of the network layer is to provide communication to the different hosts on the network.

The network layer is the third layer in the OSI reference model, which is between the transport layer and the data link layer, which further manages the data communication in the network on the transmission function of data frames between two adjacent endpoints provided by the data link layer, and tries to transmit data from the source end to the destination end through several intermediate nodes, so as to provide the most basic end-to-end data transmission service to the transportation layer. The main contents are: virtual circuit packet switching and datagram packet switching, routing algorithms, blocking control methods, protocols, integrated service data network (ISDN), asynchronous transmission mode noisy merger (ATM) and internetwork interconnection principles and implementation.

The purpose of the network layer is to achieve transparent data transmission between the two end systems, and the specific functions include addressing and routing, connection establishment, holding, and termination. It provides services that enable the transmission of this trace layer without the need to understand the data transmission and switching technology in the network.

1. ARP protocol.

Since MAC addresses must ultimately be used when transmitting data frames on links in the actual network.

How to use the ARP protocol.

Check the ARP cache, if there is a corresponding entry, write to the MAC frame, if not, encapsulate and broadcast the ARP request packet with the destination MAC address of FF-FF-FF-FF-FF, and all hosts in the same LAN can receive the sensitive request. After receiving the request, the destination host unicasts an ARP response packet to the source host, and writes the mapping to the ARP cache (updated every 10-20 minutes) after receiving the message.

There are 4 typical scenarios of ARP protocol.

2. DHCP protocol.

DHCP is an application-layer protocol that uses a client-server mode, where the client and server interact through broadcasting, based on UDP.

DHCP provides a plug-and-play networking mechanism, the host can dynamically obtain the IP address, subnet mask, default gateway, DNS server name and IP address from the server, allow address reuse, support mobile users to join the network, and support the renewal of the in-use address.

Workflow. 1.The host broadcasts a DHCP discovery packet (tries to find a server on the network, and the server obtains an IP address. ）

3.The host broadcasts DHCP request packets (the host requests the server to provide an IP address. ）

The server broadcasts a DHCP acknowledgment packet (formally assigns the IP address to the host.) ）

What are the basic parallel protocols at the network layer (no shots)?

Agreement. The agreement is stupid.

Agreement. Agreement.

Correct answer: IP protocol, ARP protocol, RARP protocol, ICMP protocol.

Layer 1: Physical layer.

To solve the problem of how to communicate between two pieces of hardware, common physical media include optical fiber, cable, repeater, etc. It mainly defines the standards of physical equipment, such as the interface type of network cable, the interface type of optical fiber, and the transmission speed and elimination rate of various transmission media.

Layer 2: Data link layer.

The data link layer receives packets, packets, from the network layer.

Contains the IP addresses of the sender and receiver. The data link layer performs two basic functions. It allows the upper layer to access the media using various techniques such as framing, controlling how data from the medium is placed and received.

Layer 3: Network layer.

The transport layer passes data segments to the network layer. The network layer is used to transfer the received data segments from one computer to another computer located in a different network. The unit of data at the network layer is called a packet, and the functions of the network layer are logical addressing, routing, and path determination.

Layer 4: Transport layer.

The main task of the lower three layers of OSI is data communication, the task of the upper three layers is data processing, and the transmission layer is the fourth layer, so this layer is the interface and bridge between the communication subnet and the resource subnet, and plays the role of connecting the upper and lower layers.

Layer 5: Session layer.

It is the interface between the user application and the network, and its main task is to organize and coordinate the communication between the two session processes and to manage the data exchange.

Sixth layer: represents the layer.

The presentation layer refers to the data received from the application layer, which is in the form of characters and numbers, and the presentation layer converts this data into binary formats that can be understood by machine bridges, that is, encapsulating and formatting data, such as converting ASCII code into other encodings, a function called "translation".

Layer 7: Application layer.

It is the highest layer of the OSI reference model, which enables the interface between computer users and various applications and networks, which are used by network applications, such as HTTPS protocol, HTTP protocol, and the application layer provides services to the network through the protocol and performs user activities.