Network Protocol Model Analysis

Network Protocol Model Analysis Network Protocol designers should not design a single, huge protocol to complete the details of all forms of communication regulations, but should divide the communication problems into multiple small problems, then a separate protocol is designed for each small problem. This makes it easier to design, analyze, and test each protocol. A major principle of Protocol Division is to ensure that the target system is effective and efficient. To improve efficiency, each Protocol should only pay attention to the communication issues that have not been handled by other protocols. To make the implementation of the master protocol more effective, the protocol should be able to share a specific data structure; the combination of these protocols should be able to handle all possible hardware errors and other exceptions. To ensure the coordination of these Protocols, the Protocol should be designed and developed into a complete, collaborative protocol series (that is, the protocol family), rather than developing each protocol in an isolated way. In the early days of network history, the International Organization for Standardization (ISO) and the International Telegraph Telephone Advisory Committee (CCITT) jointly published a layer-7 Reference Model for Open System Interconnection. Network processes in a computer operating system include application requests (at the top of the protocol stack) to network media (bottom). The OSI reference model divides functions into seven discrete layers. Figure 1 shows the OSI layered model. Layer 7 of the OSI model performs the following operations: the first layer of the physical layer is responsible for final encoding of information into a current pulse or other signals for online transmission. It consists of the actual interface between the computer and the network medium, can define electrical signals, symbols, line status and clock requirements, data encoding and data transmission connector. Such as the most commonly used RS-232 specification, 10BASE-T Manchester code and RJ-45 belongs to the first layer. All layers higher than the physical layer communicate with it through predefined interfaces. For example, the Ethernet ancillary unit interface (AUI), a DB-15 connector can be used to connect Layer 1 and Layer 2. Layer 2 data link layer provides reliable data transmission through physical network links. Different data link layers define different network and Protocol features, including physical addressing, network topology, error verification, frame sequence, and traffic control. The physical addressing (corresponding to the network addressing) defines the addressing method of the device at the data link layer. The network topology defines the physical connection mode of the device, such as the bus topology and the ring topology; error verification sends an alarm to the upper-layer protocol when a transmission error occurs. The data frame sequence is reorganized and frames other than the sequence are transmitted. throttling may delay data transmission, in this way, the receiving device will not crash because it receives information that exceeds its processing capability at a certain time point. The data Link layer consists of two independent parts: Media Access Control (MAC) and Logical Link Control (LLC ). MAC describes how to schedule, generate, and receive data on a site in a shared media environment. MAC ensures reliable cross-link information transmission, synchronizes data transmission, identifies errors, and controls data flow. Generally, MAC is only important in the shared media environment. Only nodes in the shared media environment can be connected to the same transmission media. The ieee mac rule defines an address to identify multiple devices in the data link layer. The Logical Link Control Sub-layer manages the communication between devices on a single network link. IEEE 802.2 standard defines LLC. LLC supports connectionless services and connection-oriented services. Many domains are defined in the Information frames at the data link layer. These domains allow multiple high-level protocols to share a physical data link. ARP belongs to this layer. The layer-3 network layer establishes a connection between the source and the end. It generally includes network path finding, and may also include traffic control and error checks. Data transmission between different network segments of the same MAC standard generally only involves the data link layer, while data transmission between different MAC standards involves the network layer. For example, an IP router works at the network layer, and thus multiple networks can be interconnected. IP protocol at this layer. The layer-4 transmission layer provides a reliable end-to-end network data stream service to the top layer. The functions of the transport layer generally include flow control, multi-channel transmission, virtual circuit management, error checksum and recovery. Throttling manages data transmission between devices to ensure that the transmission device does not send data that is larger than the processing capability of the receiving device. Multi-Channel Transmission allows the data of multiple applications to be transmitted to one physical link; virtual circuits are established, maintained, and terminated by the transport layer. Error verification includes various structures established to detect transmission errors, and error recovery includes the actions taken (such as request data re-transmission ), to solve any errors. Transport Control Protocol (TCP) is a transport layer protocol in the TCP/IP protocol family that provides reliable data transmission. UDP protocol belongs to this layer. The fifth layer establishes, manages, and terminates communication sessions between the presentation layer and the entity. Communication sessions include service requests and service responses that occur between different network application layers. These requests and responses are implemented through the Session Layer Protocol. It also includes creating checkpoints so that a previous status can be returned when communication is interrupted. The presentation layer of the sixth layer provides multiple functions for data encoding and conversion at the application layer to ensure that information sent at the application layer of one system can be recognized by the application layer of another system. The encoding and conversion modes of the presentation layer include public data representation format, performance conversion representation format, public data compression mode, and public data encryption mode. The common data representation format is the standard image, sound, and video format. By using these standard formats, different types of computer systems can exchange data. Conversion modes exchange information between systems by using different text and data representation, for example, ASCII (American Standard Code for Information Interchange); Standard data compression mode ensures that the compressed data on the original device can be properly decompressed on the target device; the encryption mode ensures that the encrypted data on the original device can be correctly decrypted on the target device. The presentation layer protocol is generally not associated with a special protocol stack. For example, QuickTime is the video and audio standard of the Applet computer, and MPEG is the ISO video compression and encoding standard. Common image formats such as PCX, GIF, and JPEG are different static image compression and encoding standards. The layer 7 Application layer is the closest to the end user's OSI layer, which means that the OSI Application Layer Directly Interacts with users through application software. Note: The Application layer is not composed of actual Application software running on the computer, but composed of APIs that provide the Application with access to network resources, such applications are beyond the scope of the OSI model. The functions of the application layer generally include identifying communication partners, defining resource availability and synchronous communication. Because the communication partner may be lost, the application layer must define the identification and availability of the communication partner for the Application subroutine that transmits data. When defining resource availability, the application layer must determine whether there are sufficient network resources for communication requests. In synchronous communication, communications between all applications require collaborative operation at the application layer. OSI application layer protocols include file transmission, access and management protocols (FTAM), file virtual terminal protocol (VIP), and public management system information (CMIP. The TCP/IP layered Model is called the Internet layered Model and the Internet Reference Model ). Figure 2 shows the layer-4 layer of the TCP/IP layered model. The TCP/IP protocol is organized into four conceptual layers, with three layers corresponding to the corresponding layers in the ISO Reference Model. The ICP/IP protocol family does not contain the physical layer and data link layer. Therefore, it cannot independently complete the functions of the entire computer network system and must work with many other protocols. The four protocol layers of the TCP/IP layered model provide the following functions: the network interface layer of the first layer includes the protocol used to transmit the IP data on the existing network media. In fact, TCP/IP standards do not define functions that correspond to the ISO data link layer and physical layer. Instead, it defines a Protocol like Address Resolution Protocol (ARP) that provides the data structure of the TCP/IP Protocol and interfaces between the actual physical hardware. The Layer 2 internetlayer corresponds to the network layer of the OSI Layer 7 Reference Model. This layer includes IP Protocol and RIP Protocol, which are responsible for data packaging, addressing, and Routing. It also contains the inter-network Control Message Protocol (ICMP) to provide network diagnostic information. The layer-3 Transport layer corresponds to the transport layer of the OSI Layer-7 Reference Model. It provides two end-to-end communication services. Among them, the TCP Protocol (Transmission Control Protocol) provides reliable data stream transportation services, and the UDP Protocol (Use datainprotocol) provides unreliable User Datagram services. The layer-4 Application layer corresponds to the application layer and expression layer of the OSI Layer-7 Reference Model. The application layer protocols of the Internet include Finger, Whois, FTP (file transfer protocol), Gopher, HTTP (Hypertext Transfer Protocol), Telent (Remote Terminal protocol), and SMTP (Simple Mail Transfer Protocol), IRC (Internet Relay Session), NNTP (network news transmission protocol), etc. OSI Layer-7 model TCP/IP layer-4 model transmission data application layer data presentation layer data Session Layer data transmission layer network layer Internet layer package data link layer network interface layer frame physical layer network interface layer bit differences and relationships between network hardware devices corresponding to the stream: 1. A repeater is a network device located at the layer 1st (the physical layer of the OSI reference model. When data leaves the source for transmission over the network, it is converted to electrical pulses or optical pulses that can be transmitted along the network media-these pulses are called signals ). When the signal leaves the transmission workstation, the signal is planned and easily identified. However, when the signal is transmitted along the network medium, the signal will become weaker and worse as the passing cable grows. The purpose of a repeater is to regenerate and repeat network signals at the bit level so that they can transmit longer distances over the network. 2. The basic function of a hub is information distribution. It distributes all signals received by a port to all ports and works at the physical layer (bottom layer ). Actually, it is a multi-port repeater (sort out the signals that are not completely degraded, generate a complete signal, and then transmit it again ). 3. Bridge is a storage and forwarding device connected to two local networks. It can be used to connect networks with the same or similar architecture. In a LAN composed of hubs, a large number of hosts communicate with each other through arp broadcast to distribute data. In order to reduce the medium contention (conflict) in the shared environment, bridges generate, it divides broadcast domains into a small conflict domain, and selects forwarding information through addressing and paths. The traffic between workstations on a network segment is limited to the scope of this segment, instead of going through the bridge to other network segments. It can reduce the traffic, which increases the available bandwidth, but the broadcast domain remains unchanged. The bridge works at the Layer 2 data link layer. It connects two LANs and forwards Frames Based on the MAC address. It can be seen as a "low-layer Router" (the router works at the network layer, based on the network address, such as the IP address, and the port number is very small (note the difference with the following switch ). Bridges are divided into two categories: local bridges and remote bridges. Local bridges are mainly used to provide direct connections between multiple LAN segments in the same geographic area. Remote bridges are used to connect LAN segments in different regions. 4. the gateway function is to repackage the information to meet the requirements of the target network environment. The gateway implements communication between different architectures and environments. After the data is reconverted by the gateway, it can enter another network environment from one network environment, enables various network environments to understand and communicate with each other's data, and provides protocol conversion facilities on the OSI network layer. 5. The switch is actually a multi-port bridge, so both the bridge and the switch have the switching function. The switch has the ability to automatically address and exchange information. Based on the destination address of the transmitted information package, each information package uses a high-bandwidth back bus and an internal switching matrix, the source port is sent to the destination port independently to avoid collision with other ports. If the target MAC does not exist, the switch broadcasts all the ports. After receiving the port response, the switch "learns" the new address and adds it to the internal address table. Seeing the role of the bridge, people developed it into a multi-port device, and integrated the hub function, invented the switch, the switch also works on the second layer. In addition to bridging (that is, isolating conflicts) and forwarding data packets, a switch also has other advanced features, such as vlan (Virtual LAN), port trunking (connection aggregation ), spanning tree (spanning tree) and other features. High-end switches also provide routing functions. The specific routing functions will be described later. A vswitch is a dedicated network device based on hardware, so it has a higher data forwarding capability than a software-based bridge. The switch allows devices connected to the switch to communicate in parallel. Communication between devices does not conflict with each other. Therefore, the switch breaks the conflict domain. Each interface of the switch is a conflict domain, does not conflict with other interfaces. However, the vswitch and the hub cannot determine the broadcast data packet and send the broadcast to all interfaces. Therefore, the vswitch and the hub are connected to a broadcast domain network. In addition, a system switch can record the MAC address table, and the sent data is not sent to each interface in broadcast mode, but directly to the Target Interface, saving the interface bandwidth. A high-end switch can not only record MAC address tables, but also divide VLAN (Virtual LAN) to isolate broadcast, but also cannot communicate between VLANs. To enable communication between VLANs, a layer-3 device must be involved. 6. With the further development of the network, it is troublesome to select a route between widely distributed networks, therefore, a dedicated network hardware is generated-a router. A vro works on Layer 3 (Network Layer). It also involves Layer 2 and Layer 1, but its main purpose is to select routes. Vro memory stores route tables, which are easy to change and are easy to change. The route table includes the next hop route address to the destination address, the Management Distance between different addresses, and so on. The route table content is learned after the vro is started. After the vro is started, it exchanges information with other vrouters Based on the configured routing protocol and learns the route during information exchange. Therefore, although a router is a hardware-based dedicated network device, the routing algorithm supported by the router is the core. There are two types of routing algorithms: distance vector algorithms (such as rip and igrp), connection status algorithms (such as ospf), and balanced hybrid algorithms (such as VPN ), is the synthesis of the previous two algorithms. The router uses the distance vector algorithm to determine the priority path to the destination address. There is only one standard, that is, the number of hops. The path with the minimum number of hops is the most path, regardless of bandwidth, reliability, latency, and other factors. In addition, it is considered that the destination address with more than 15 hops cannot be reached. This restricts the optimal path for classless routing, and the number of routable regions increases, and balance the traffic between various links. A vro not only isolates conflicting domains like a vswitch, but also has a function that a layer-2 device does not have, that is, isolated broadcast. It can restrict broadcast within a network, increase the bandwidth between networks. Vro intervention enables communication between VLANs divided by vswitches. Summary: hubs are hardware-only, used to connect to network terminals, and cannot break the conflict domain or broadcast domain. Network Bridge: A layer-2 device used to isolate conflicts, but not broadcast. It is often software-based and is rarely used now. Vswitch: it has a software system and is used to connect to a network terminal. It can break the conflict domain, but cannot split the broadcast domain. It is a multi-port L2 device with functions in addition to the functions of the bridge, as well as its specific advanced features. Vro: it has a software system and is used for path selection. It can break through conflicting domains or separate broadcast domains. It is a ratio slave device that connects to large networks. In general, bridges cannot replace switches (because they are single-port), while bridges and switches cannot replace gateways. They cannot connect two different networks. The gateway can act as a bridge. A vswitch uses a physical address or a MAC address to determine the destination address for data forwarding. A vro uses the idnumber (IP address) of different networks to determine the data forwarding address. Summary of common related Interview Questions: Division of various layers of the OSI reference model principles: 1. Each network node on the same layer has the same hierarchy and has the same function. 2. interfaces (logical interfaces) are used to communicate with adjacent layers of the same node. 3. Each layer in the layer-7 structure uses the services provided by the next layer and provides services to the upper layer. 4. Communication between peer layers is achieved at the same layer of different nodes according to the protocol. The first layer: Physical Layer (PhysicalLayer), which specifies the mechanical, electrical, functional, and process characteristics of communication equipment for establishing, maintaining, and removing physical link connections. Specifically, the mechanical characteristics specify the specifications, sizes, number of pins, and arrangement of connectors required for network connection; the electrical characteristic specifies the signal level, impedance matching, and transmission speed limit on the line when the bit stream is transmitted on the physical connection. The function characteristic refers to assigning the exact signal meaning to each signal first, that is, the function of each line between DTE and DCE is defined. The procedure feature defines a set of Operation Procedures for bit stream transmission using signal lines, it refers to the operation series in which DTE and DCE are placed on each circuit during the establishment, maintenance, and exchange of information on physical connections. At this layer, the unit of data is bit ). Representative of typical specifications defined by the physical layer include: EIA/TIA RS-232, EIA/TIA RS-449, V.35, RJ-45, etc. Layer 2: data link layer (DataLinkLayer): establishes data links between adjacent nodes based on the bit stream service provided by the physical layer, and provides Frame transmission without errors through error control, and carries out the action series on each circuit. The data link layer provides reliable transmission on unreliable physical media. The role of this layer includes physical address addressing, data frame formation, traffic control, data error detection, and re-transmission. At this layer, the unit of data is frame ). Data link layer protocols include SDLC, HDLC, PPP, STP, and frame relay. The third layer is that the two computers that communicate in the computer network at the network layer may pass through many data links or through many communication subnets. The task at the network layer is to select an appropriate inter-network route and exchange node to ensure timely data transmission. The Network Layer encapsulates the frames provided by the data link layer into a data packet. The packet contains a network packet header, which contains the logical address information-the network address of the source site and the destination site. If you are talking about an IP address, you are dealing with layer-7 problems. This is a "packet" problem, not a "frame" of layer-7 ". IP addresses are part of Layer 2 issues. In addition, there are some routing protocols and IP Address Resolution protocols (ARP ). Everything about routing is handled at Layer 3rd. Address Resolution and routing are the important purposes of Layer 3. The network layer can also implement congestion control, Internet interconnection, and other functions. At this layer, the unit of data is called packet ). Network Layer Protocols include IP, IPX, RIP, and OSPF. The fourth layer is the transmission layer for processing information. The data unit at Layer 3 is also called packets ). However, when you talk about specific protocols such as TCP, there is a special name. TCP data units are called segments, while UDP data units are called "datagram Rams )". This layer is responsible for obtaining all information. Therefore, it must track data unit fragments, unordered data packets, and other possible risks during transmission. Layer 3 provides an end-to-end (end user to end user) transparent and reliable data transmission service for the upper layer. Transparent transmission means that the transmission layer shields the details of the communication transmission system from the upper layer during the communication process. The Transport Layer Protocol includes TCP, UDP, and SPX. The fifth layer is the Session Layer, which can also be called the meeting layer or dialogue layer. At the session layer and above, the data transmission unit is no longer named as another packet. The Session Layer does not participate in specific transmission. It provides a mechanism to establish and maintain communications between applications, including access authentication and session management. For example, the Session Layer completes the authentication of user logon on the server. The sixth layer is the presentation layer, which mainly solves the problem of supporting the syntax expression of information. It converts the data to be exchanged from an abstract syntax suitable for a user to a transfer syntax suitable for internal use within the OSI system. It provides formatted data representation and Conversion Services. The presentation layer is responsible for data compression, decompression, encryption, and decryption. The layer 7 Application Layer provides interfaces for operating systems or network applications to access network services. Application layer protocols include Telnet, FTP, HTTP, and SNMP. Through the OSI Layer, information can be transmitted from a computer's software application to another application. For example, if an application on computer A sends information to an application on computer B, the application on computer A needs to first send the information to its application layer (Layer 7 ), this layer then sends the information to the presentation layer (layer 6), which transfers the data to the Session Layer (layer 5) until the physical layer (Layer 1 ). At the physical layer, data is stored in the physical network medium and sent to computer B. The physical layer of computer B receives data from physical media and sends the information to the data link layer (Layer 2). The data link layer then forwards the information to the network layer until the information reaches the application layer of computer B. Finally, the application layer of computer B transmits information to the application receiver to complete the communication process. The following figure shows the process. Layer 7 of OSI uses various control information to communicate with the corresponding layers of other computer systems. These control information contains special requests and descriptions that are exchanged between the corresponding OSI layers. The header and tail of each layer of data are two basic forms of carrying control information. For the data transmitted from the previous layer, the control information appended to the previous layer is called the header, and the control information appended to the previous layer is called the tail. However, adding protocol headers and Protocol tails to data from the previous layer is not necessary for an OSI layer. When data is transmitted between layers, each layer can add headers and tails to the data, and the data already contains the headers and tails added to the previous layer. The protocol header contains the communication information between the layer and the layer. Headers, tails, and data are associated. They depend on the protocol layer of the analysis information unit. For example, the transport layer header contains information that can only be seen by the transport layer. Other layers under the transport layer only transmit this header as part of the data. For the network layer, an information unit consists of the header and data of the third layer. For the data link layer, the layer-3 header and data are considered as data. In other words, in a given OSI layer, the data part of an information unit includes the header, tail, and data of all upper layers. This is called encapsulation. For example, if computer A wants to send data from an application to computer B, the data is first transmitted to the application layer. The application layer of computer A communicates with the application layer of computer B by adding A protocol header to the data. The information unit consists of the protocol header, data, and Protocol tail. It is sent to the presentation layer and then added as the protocol header of the control information understood by the presentation layer of computer B. The size of information units increases with the addition of each layer of protocol header and Protocol tail. These protocol headers and Protocol tails contain the control information to be used by the corresponding layer of computer B. On the physical layer, the entire Information Unit is transmitted through network media. The physical layer in computer B receives information units and sends them to the data link layer. Then, the data link layer in computer B reads the control information in the protocol header added to the data link layer of computer; remove the protocol header and end, and the rest is sent to the network layer. Each layer performs the same action: Read and remove the protocol header and end from the corresponding layer, and then send the remaining information to the first layer. After these actions are performed on the application layer, the data is transmitted to the application program in computer B, which is exactly the same as that sent by the application program in computer. The communication between one OSI Layer and the other layer is completed using the services provided by the second layer. The services provided by the adjacent layer help one OSI layer to communicate with the corresponding layer of another computer system. A specific layer of an OSI model is usually associated with the other three OSI layers: directly adjacent to the upper and lower layers, as well as the corresponding layers of the target networked computer system. For example, the data link layer of computer A should communicate with its network layer, physical layer, and data link layer of computer B to determine the electrical and physical properties of the connected device. The data link layer B is responsible for transmitting frame-based data without errors through detection, traffic control, re-transmission, and other means on the line between network nodes. To achieve this, synchronization, address, error control, traffic control, and other control information must be included in each frame. In order to send data groups from the source (source) to the destination (target), the task at the network layer is to select a proper route and exchange node, the packet information transmitted from the source transport layer can be correctly identified by the address and delivered to the corresponding transport layer to complete the network addressing function. D. the transport layer is the interface layer connecting the high and low layers. The unit of data transmission is a packet. When the packet is long, it is divided into several groups and then handed over to the network layer for transmission. The transport layer is the most critical layer in the computer network protocol hierarchy. The above layers no longer manage information transmission issues. E Session Layer this layer provides synchronous management services for transmitted packets. Establish, organize, and coordinate interactions between application processes that communicate with each other in two different systems. For example, determine whether it is duplex or half duplex. F presentation layer the main task of this layer is to transform the abstract syntax of the transmitted data into the transfer syntax, that is, to convert different representations within different computers into standard representations in network communication. In addition, data encryption (or decryption) and body compression (or restoration) are also tasks of the presentation layer. G Application Layer this layer is directly oriented to users and is the highest level in OSI. Its main task is to provide users with application interfaces, that is, to provide file transfer, access and management between different computers, and to process email content, virtual terminal functions accessed by different computers through network interaction. 2. TCP/IPa network interface layer is the lowest layer of TCP/IP protocol, including multiple Logical Link Control and media access protocols. The function of the network interface layer is to receive IP datagram and transmit it through a specific network, or to receive physical frames from the network, extract the IP datagram and transfer it to the Internet layer. B Internet layer (IP layer) This layer includes the following protocols: IP (Internet Protocol), ICMP (Internet Control Message Protocol, Internet Control Packet Protocol), ARP (Address Resolution Protocol, address Resolution Protocol), RARP (Reverse Address Resolution Protocol, Reverse Address Resolution Protocol ). This layer is responsible for communication between computers in the same or different networks and mainly processes datagram and routing. On the IP layer, ARP is used to convert an IP address to a physical address, RARP is used to convert a physical address to an IP address, and ICMP is used to report errors and transfer control information. The IP protocol is at the core of the TCP/IP protocol group. C Transport Layer this layer provides two Protocols: TCP (Transport Control Protocol) and UDP (User datagrams Protocol), both built on the basis of the IP Protocol, among them, TCP provides reliable connection-oriented services, and UDP provides simple connectionless services. The transport layer provides end-to-end communication between applications. Its main functions include data formatting, data validation, and loss retransmission. The Application Layer of the d Application Layer TCP/IP protocol is equivalent to the Session Layer, presentation layer, and application layer of the OSI model. It provides users with a set of common application layer protocols, including Telnet, SMTP, and DNS. In addition, user applications are included in the application layer, all of which are dedicated programs built on TCP/IP protocol groups. 3. Differences between the OSI reference model and the TCP/IP Reference Model: The a OSI model has 7 layers, and the TCP/IP model has only 4 layers. The B OSI model is prior to the Protocol, therefore, it will not be biased towards any specific set of protocols and is more universal, but some features do not know which layer should be placed, so some sub-layers have to be added; TCP/IP appears after the Protocol, it is only a description of an existing protocol, so the two work very well together; but it is not suitable for other protocol stacks and is not easy to describe other non-TCP/IP networks; in c OSI, the network layer supports connection-free and connection-oriented communication at the same time, but only connection-oriented communication at the transport layer. In TCP/IP, the network layer only supports connection-free communication, the Transport Layer supports two types of communication at the same time. d. When technology changes, the OSI model is easier to replace than the protocols in the TCP/IP model. -------------------------------------- Q2: Please explain in detail the definition of the IP protocol, on which layer, what is the main role? What about TCP and UDP? Solution: three protocols are used together with the IP protocol: ARP-Address Resolution Protocol RARP-Reverse Address Resolution Protocol ICMP-Internet Control Packet protocol ICMPIP protocol-Internet Protocol IP address, IP packet header ------------------------------------ Q3: What are the implementation principles of vswitches and vrouters? At which level is the implementation implemented? Some intermediate devices (or intermediate systems) are used to connect networks. ISO is called relay Systems. According to the level of the relay system, there can be five relay systems: 1. Physical Layer (the first layer, layer L1) repeater ). 2. data link layer (Layer 2, layer L2), that is, bridge or bridge ). 3. The network layer (Layer 3, layer L3) relay system, that is, the router ). 4. A mixture of bridges and routers. brouter has the functions of bridges and routers. 5. A relay system above the network layer, that is, a gateway ). when the relay system is a forwarder, it is generally not called network interconnection, because it only expands a network, and it is still a network. High-level gateways are rarely used due to their complexity. Therefore, network interconnection generally refers to the network in which vswitches and vrouters are interconnected. This article describes the differences between vswitches and vrouters. What is the difference between a Layer 2 switch and a router: a traditional switch developed from a bridge and belongs to an OSI Layer 2, that is, a data link layer device. It selects routes from the station table based on MAC address addressing. The establishment and maintenance of the station table is automatically implemented by the switch. A router is a layer-3 network-layer device of OSI. It is addressing based on IP addresses and is generated through the route table routing protocol. Internet routing protocol: the difference between the IGP protocol and the EGP layer-3 Switch and router: before the emergence of layer-3 switching technology, there is almost no need to distinguish the routing feature from the router. They are exactly the same: providing the routing feature is working on the router. However, currently, layer-3 vswitches can fully perform most of the functions of traditional routers. To sum up, the switch is generally used for the LAN-WAN connection, the switch belongs to the bridge, is the data link layer equipment, some switches can also realize the third layer of the exchange. A vro is used for WAN-WAN connections. It can resolve forwarding groups between different networks and act on the network layer. They only accept the input group from one line and then forward it to another line. These two lines may belong to different networks and adopt different protocols. In comparison, vro features more powerful than vswitches, but the speed is relatively slow and expensive. layer-3 vswitches have both the ability to forward packets at the wire speed of vswitches and the good control function of vrouters, therefore, it can be broadcast applications. 1: Would you like to draw a layer-7 OSI network structure and a layer-5 TCP/IP network structure respectively? The layer-7 network structure of OSI and the layer-5 structure of TCP/IP are short for the Open System Interconnect, meaning the interconnection of Open systems. Prior to the emergence of OSI, there were numerous architectures in the computer Network, with IBM's SNA (System Network Architecture) and DEC's DNA (Digital Network Architecture) the digital network architecture is the most famous. In order to solve the Interconnection problem between networks of different architectures, ISO (do not mix with OSI) developed the Open System Interconnection Reference Model (Open System Interconnection Reference Model) in 1981, OSI/RM ). This model divides Network communication into seven layers, which are Physical Layer (Physical Layer), Data Link Layer (Data Link Layer), and Network Layer (Network Layer ), transport Layer, Session Layer, presentation Layer (Presen tation Layer), and Application Layer ). The layer 1 to Layer 3 belongs to the lower layer of the OSI reference model and is responsible for creating network communication links. The Layer 4 to Layer 7 is the high-level layer of the OSI reference model, which is responsible for end-to-end data communication. Each layer provides certain functions, each layer provides services for its upper layer, and all layers support each other, while network communication can be top-down (on the sending end) or two-way implementation from the bottom up (at the receiving end. Of course, not every message needs to pass through all Layer 7 of OSI, and some even only need a layer corresponding to both parties. The transfer between physical interfaces and the connection between the repeater and the repeater only needs to be performed in the physical layer. The connection between the router and the router only needs to pass through the Layer 3 below the network layer. In general, the communication between the two parties is at the peer level and cannot be at the asymmetric level.