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There are a large number of intermediate nodes in the Internet. If the user uses a connectionless protocol to transmit a data stream, each datagram of the data stream may cause two problems when it is forwarded through an intermediate node. One is that the forwarding path of each datagram is different and does not arrive at the destination in order. Some data Packets may arrive late; second, when data packets are queued at intermediate nodes for forwarding, their queuing time is uncertain, and when intermediate nodes are congested due to lack of resources, packet loss strategies will be adopted to divert traffic. For end-to-end communication, it means transmission delay and delay jitter. These are all disadvantages for multimedia communication, and seriously affect the service quality of end-to-end multimedia communication. The basic method to solve this problem is that the endpoint and the intermediate node should cooperate closely, based on the connectionless protocol, establish a

I have learned network technology for a long time, but what is the difference between a Layer 3 switch and a router? Many people will still be confused. So what is the difference between them, we need to understand it carefully. The simplest working principle of Layer 2 switches is to perform data forwarding operations based on the MAC address table. There are four basic functions:  learning, forwarding, broadcasting and updating. When a data frame is received, the switch will store the mapping relationship between the source MAC address of the data frame and the corresponding port number in the MAC address table for subsequent data forwarding. However, in this line of data forwarding, the target MAC address is used, and the MAC address table is queried. If the MAC address table has a corresponding mapping relationship, the data frame will be unicast forwarded. If there is no corresponding mapping relationship, a generalization will be performed. flood. Another very important fe

OpenFlow can be used to control and manage the switching module by the controller. The OpenFlow channel is established between the controller and the exchange module to realize information exchange. When the switching module establishes multiple connections with multiple controllers through OpenFlow, then the controller will inform the switching module of its role through the OpenFlow channel. Subsequently, the controller delivers the forwarding information database or flow table to the switching module through the OpenFlow channel. Data forwarding is accomplished by the exchange module performing protocol calculations based on the forwarding information database to generate ARP entries, or based on flow table information. By establishing an OpenFlow channel, before implementing information exchange between the controller and the exchange module, you need to understand the process of establishing and maintaining the openflow channel. It is also necessary to maintain the openflow

Types of OSPF packets Hello: Used to establish and maintain neighbor relationships. It is sent once every 10 seconds and timed out after 30 seconds. hello, area-id, authentication, stub Passive-interface, MTU, and an ACL on the interface filter OSPF traffic Five OSPF messages 1. HELLO 2. LSU 3. LSR 4. DBD: Directory 5. LSACK   Three tables of OSPF   Topology table (LSDB): the same LSDB in the same area Neighbor table: also called neighbor state database Routing table: the best path to the target network Various types of LSA Point-to-point broadcast The reason is because LSDB is not synchronized Point-to-point does not elect DR, no type 2 LSA Broadcast has type 1 LSA type 2 LSA LSA: 1 2 3 L1 Content: This router announces the link information to OSPF, Who generated it: OSPF router Scope of spread: Flooding in the area L2 What routers are in this area DR Flooding in the area L3 LSA in other regions ABR Flood to the entire AS,

FTP (FileTransfer Protocol)   is used to transfer files between a remote server and a local host, and is a general protocol for transferring files on an IP network. Before the advent of the World Wide Web (WWW, World Wide Web), users used the command line to transfer files, and the most common application was FTP. Although most users currently choose to use Email and Web to transfer files under normal circumstances, FTP still has a relatively wide range of applications. The FTP protocol belongs to the application layer protocol in the TCP/IP protocol family. It is used to transfer files between a remote server and a local client, and uses TCP ports 20 and 21 for transmission. Port 20 is used to transmit data, and port 21 is used to transmit control messages. The basic operation of the FTP protocol is described in RFC959. FTP supports two modes, one is called Standard (that is, PORT mode, active mode), and the other is Passive (that is, PASV, passive mode). Standard mode FTP clie

Wi-Fi 6 and 5G technologies will play an increasingly important role in the future, but enterprises will still tend to use Wi Fi 6 to create internal connections. Today, the enterprise IT environment is rapidly becoming a data-centric, widely distributed environment, including tens of billions of smart devices that need to be connected. This will form the Internet of Things (IOT) and use artificial intelligence (AI), machine learning, big data, and advanced analytics to generate petabytes of data, multiple public and hybrid clouds, and modern applications. The core of all this is the wireless network, which can support all these devices, move all data, link all these cloud platforms, and meet the speed, capacity, and latency requirements of these modern workloads. Wi-Fi 6 and 5G (the latest versions of Wi-Fi and cellular protocols) have entered the world. Wi-Fi 6 and 5G are designed to meet all the demands of an increasing number of devices and users, as well as an increasingly

Today we will consolidate the most basic Cisco DTP protocol in detail. The Cisco Dynamic Trunking Protocol DTP is all the protocols of Cisco in the  VLAN group. It is mainly used to negotiate the trunking process and trunk encapsulation 802.1Q type on the link between two devices. DTP is cisco's proprietary protocol. It can only be used to establish trunk links between switches and send DTP frames every 30s. DTP uses negotiation to decide whether to configure the interface as a trunk. When a trunk link is required, the interface mode is usually manually configured statically, and the trunk encapsulation protocol is manually specified.   When the switch is connected to the interface of the switch, most of them need to be configured in Trunk mode; when the switch is connected to the host, they need to be configured in access mode. There are many different types of relay protocols. If the port is set to  Trunk  port, then the port has automatic trunking function, and in some

Today we will review and self-check the brief description of the EIGRP protocol DUAL dispersion update algorithm. Diffusing Update Algorithm , or diffusion update algorithm, is one of the EIGRP components and provides the best routing path for EIGRP. DUAL is a method for EIGRP to determine the best loop-free path and loop-free backup path. We must first understand these terms: 1) easydistance, FD:  refers to the smallest metric for the router to reach the destination network. 2) reporteddistance, RD:  the feasible distance from the EIGRP neighbor to the same destination network. The reporting distance is a measure of the cost that the router reports to its neighbors about its own access to the network. 3) easycondition, FC:  When the reported distance (RD) of the neighbor to a network is shorter than the feasible distance from the local router to the same destination network, the feasible condition (FC) is met. 4) Successor:  The neighboring router that meets the feasible