Switcher, three switches, four switches distinction Two-exchange technology is relatively mature, the switcher is the data link layer device can be used to identify data packets to the MAC Information site, according to MAC address for forwarding those MAC addresses with the corresponding port to a record in its internal Site table. Specific work flow as follows : (1) When the switchboard received a packet from one port, which first read the source MAC address of the contractor, so that it knows Source MAC address of the machine which is linked to the port; (2) the purpose of again capturing Baotou MAC address and find the corresponding port in the address table; (3) If the MAC address table with the corresponding port this purpose, data packets directly to this port complex system; (4) If the port took the form not corresponding data packet radio to all ports, as the purpose machines to respond to the source machine , A switch can learn MAC addresses with the purpose of which Port counterparts in the next transmission of data no longer need to have A port for broadcast. The constant cycle of this process, the MAC address information for the entire network can learn, and is built switcher Table safeguard its own address. The working principle from the switcher can deduce the following three points : (1) Since the majority of Port Switch for the simultaneous exchange of data, which requires a very broad exchange of bus bandwidth. If there are N-port switcher, the bandwidth of each port is M, M × N switch over bus bandwidth, this exchange Exchange-rate mechanism can be achieved; (2) study linking the port machinery MAC address into the address table size of the address table (usually two expressions : One BEFFER RAM, a table of items numerical MAC) address table size of the impact of exchange access capacity; (3) there will be a general switcher is designed for use with data packets are transmitted with the ASIC (Applicati On specific Integrated Circuit) chip, it can be done extremely fast forwarding speed. As all manufacturers ASIC use, a direct impact on product performance. Performance evaluation is three points above the merits of the two main technical parameters of the three-tier exchange, I urge you to consider Equipment Selection At the comparison. (2) Routing Technology Routers in the network layer OSI model -- the third operation, the second floor of the exchange and its mode similar to that for routers For the third layer, the routing and switching decisions of this distinction in the use of different control information packet transmission, the function of the square - Different. The working principle is in the road, there are also a table showing the table is a way to go if Side, there should be the next step to take, if data packets from the routing table to find where to go next, and link layer information Out with transponders; If not know where the next step, it will send the packet away, then returned to a source of information Address. But two functions : routing technology Substantively determine the optimal routing and transmitting data packets. Routing Table to include all kinds of information By the arrival address routing algorithm calculated the optimal route, and then sent by the relatively straightforward mechanism for transmitting data Packets. Data path for Taiwan to accept the next to continue to work with the same transponders that, and so on until the arrival of data packets Purpose routers. And the routing table maintenance, there are two different ways. One is the updated routing information to some or all of the routing No. out information, learn from each other routing information through routers, the entire network topology on the other hand, this type of routing Agreement called distance vector routing protocol; Another path is the link status information for their broadcasts, through mutual Learn the entire network routing information, and then calculate the best path forwarding, routing protocols such as Link State Routing Agreement. Since the router needs to be done in the path calculation, the general processor's ability to directly determine the performance of the pros. Of course, this judgment or to the mid - and low-end routers, is often used as high-end routers based Distributed Processing System Dollars. (C) Layer 3 Switching Technology In recent years the technology of the three-tier publicity ears cocoon son can play everywhere, shouting at the three-tier technology, it was said that this is a very New technologies are also those who say that the three-tier exchange say, is not stacking switcher and router, and no new Game, this really true? Next, we will look to the network through a simple process of layer 3 switches. Relatively simple network The use of IP equipment A------------------------ ------------------------ use IP Layer 3 Switch B equipment A B transmission to give such information, known purpose IP, subnet mask made concerning use of network addresses, IP with the goal judge In the same network segment. If the same network segment, but I do not know the MAC address transmitted data, it sent a ARP请求 A, B return to the MAC Site A MAC encapsulated data packets sent out with this exchange, the use of two-exchange module, to find out the MAC address table, Data packets transmitted to the corresponding port. If the aim was not to the same IP address of the network, then A and B to achieve communication, no corresponding entries in the flow cache MAC address entries, it will be a normal data packet sent to a default gateway, the gateway default operating system in general Has been set up, corresponding to Level 3 routing module, the data shows that for those who are not the same subnet, in the first table up MAC Default Gateway is the MAC address; Then data packets from the three modules now receiving inquiries routing table to determine the arrival B Routing will be constructing a new DLCI, with the MAC address of the default gateway MAC source address, MAC address to the mainframe B MAC address for the purpose. Recognition by a trigger mechanism, established mainframe A and B transponders port MAC address and the corresponding relations Relations and record flow into the cache entry forms, after the data from A to B, on the second floor of the exchange directly by the module. This links Said repeatedly transmitted a regular routing. The above is a brief summary of the three-tier exchange process, we can see a three-tier exchange features : Hardware by combining the high-speed data transmitted. This is not a simple case of the switcher and router stack, routing module directly superimposed on the second floor of the three-tier exchange of high-speed back Bus board, the restrictions of traditional routers adapter rate, the rate can be several Gbit. Count backplane bandwidth, Performance of these two important parameters of the three-tier exchange. Routing simple routing software to simplify the process. Most of the data transmitted, in addition to the necessary routing by routing software is another two-story modular high-speed forwarding. Most are processed efficiently routing software optimization software is not simply follow the path for the software. Conclusion Switcher for small LANs. I need not elaborate on this, in small LAN, packet radio little effect , The rapid exchange of the switcher functions, and a number of low-price access port for small network users with a very sound Solution. The advantage is that the road is rich adapter support the three powerful, powerful routing capabilities, suitable for large-scale The routing network, it has the advantage of being to select the best routing, load sharing, and other network routing and link backup Path for the exchange of information and so on which is functional. The most important function of layer 3 switches to speed up large-scale LAN is the rapid internal data transmitted by adding routing function For the purpose of the service. If the major networks in accordance with the department, divided into geographical factors of a small LAN. This will lead to a large number of Internet visits, using a simple Internet visits achieved switcher; If using a simple routing Device, as several Adapter Routing transmitted slow and limited, the network will limit the speed and scale of the network using routing Fast-Forwarding function of the three-tier exchange has become the first choice. In general, including net flow of data, transmitted rapid response requirements of the network, such as switches do this all by three Work will create too heavy a burden for layer 3 switches, response speed affected by the routing path for the network to complete To give full play to the advantages of different equipment, it is a network strategy, of course, the prerequisite is the customer's pocket is very dark, Otherwise it the second best, and also allow for Internet interconnection layer 3 switches. The fourth tier exchange of a simple definition : It is a function not only of its decision to transfer based on the MAC address (Layer 2 network Bridge) or source / target IP address (layer 3 routing), but based on TCP and UDP (4th floor) port its applications. The fourth tier exchange Gong Virtual IP as can be, at the physical server. It transmission business subject to a variety of agreements, HTTP, FTP, NFS , Telnet or other agreement. These business in the physical servers based on the complex needs of the load balancing algorithm. IP World Industry, the type of business TCP or UDP port address from the terminal to determine the interval from the fourth floor of the exchange and eventually Source End IP address, port TCP and UDP over a common decision. In the fourth exchange for the use of the server group set up to search for each virtual IP address (VIP), each server support Certain applications. Domain name server (DNS) of storage for each application server addresses are VIP, which is not true service Device addresses. When a user application for a target server group with a VIP listening (such as a TCP SYN packets) made Switch to the server. Switch select the best server in the server group, will address the VIP terminal with the actual service The IP replaced by listening and will pass on the server. Thus, all packets from the same interval for video server switches Launched in transmission between users and the same server. The fourth tier exchange Principle The fourth layer is the transport layer OSI model. Transport layer is responsible for end-to-end communications network in coordination between the source and target system Communication. This is a TCP-IP Protocol Stack (a transmission protocol) and UDP (User Datagram Protocol), where the protocol layer. In the fourth layer, including TCP and UDP over heading port (portnumber), which can only distinguish between each data packet Which includes application protocol (such as HTTP, FTP, etc.). Endpoint systems use this information to differentiate packets of data, especially Port is a receiver so that its computer system to determine which types of IP packet received, and turned it over to the appropriate senior Software. The combination of IP address and port equipment, often called a "socket (socket)." Between 1 and 255, were retained in the port, which they call the "known" port, which means that all mainframe TCP P. Stack, these ports was the same. In addition to "known" port, standard UNIX distribution services to the 256 1024 port, customized application in the 1024 general distribution over its port. The latest inventory in the distribution Port RFc1700 "Assigned Numbers" found. TCP and UDP end Additional information can be provided by the slogan used for network switches, and this is the first exchange on the basis of four storeys. "Familiar" for its Port : 　　 Port Application Protocol No. FTP 20 (data) 21 (Control) TELNET 23 SMTP 25 HTTP 80 Typically 119 NNMP 16 162 (SNMP traps) Additional information can be provided by the TCP and UDP ports to its network switches are used, which is the fourth exchange. The fourth function is to play a switchboard connecting with the server in a "virtual IP" (VIP) front-end role. Per server and application server support for the overall group are single or a VIP configuration address. The VIP addresses were sent out To the domain name registration system. Issued a service request, the fourth judge to TCP layer switches, the identification of the beginning of a conversation. However After its use of complex algorithms to determine the best server to deal with the request. Once such a decision would Switch Conversational associated with a specific IP address and IP address with the real server to replace the server to the VIP Site. Each of the fourth and switches have been preserved with a choice of server and the source TCP port phase match 源IP地址 Table linking interrelated. This server and then transmitted to the fourth level switches listening. Follow-up with all wrapped in client service Alluding to the Treasury and re-transmitted between devices, until the conversation switches found so far. In the fourth level of the exchange, access servers can be linked together to meet with real users in the regulation , And so as there are an equal number of each server access to distribution or transmission capacity of the server under different flow. How to choose an appropriate level of the fourth exchange A speed To be effective in the enterprise network, the fourth level of exchange must be provided with the third wire-speed routers can be compared to the performance. Also In other words, the fourth level of the exchange rate in all port operations to the entire media, even in a number of Gigabit Ethernet links also So. Gigabit Ethernet data rate of 1.488 million packets per second equivalent to the maximum speed routing (assuming the worst case, All packages and network definition of the minimum size of 64 bytes long). B, server capacity balancing algorithm Based on the desired balance between capacity interval size allocated to the fourth tier application server switches to a variety of algorithms. The recent linking is a simple loop detection, detection or server delay the detection loop feedback loop. In all the pre - Measurement, the volume of the existing closed-loop feedback to provide the most accurate server testing. C, table capacity It should be noted that the need for a fourth exchange switchboard distinction and the ability to store a large number of items sent table. Switch In particular the core of an enterprise network. Many second / 3 Switch inclined to send the form and size of the network equipment Proportional to the number. On the fourth level switches, must be multiplied by the number of different networks used in the application of the oral agreement and a few Volume. Thus sending endpoint table with the size of the increase in the number of types of equipment and application of rapid growth. Fourth Switch Design Need to be considered in the design of its products at the table this growth. The large scale manufacturing capacity to support wire-speed flow of transmission fourth High Performance Switch is essential. D, redundancy Fourth layer switches support redundant internal topology function. In a double-fault-tolerant network adapter connecting link, and then Server to be built from a network adapter, link and the exchange of fully redundant server system. Switcher, three switches, four switches distinction Up^ Switcher, three switches, four switches distinction Top-ing. . . . Switcher, three switches, four switches distinction The top [ Closed window ]