In combination with the two articles, respectively, simple, complex narrative of multilayer switching technologies in the OSI
The following is taken from: http: //www.10tiao.com/html/249/201502/203264551/1.html
Jane: in the end what is "four / seven" switching technology?
Floor of the exchange
Exchange principle: for data exchange according to the MAC address of the end data link layer of the second layer;
work process:
(1) The switch port receives a data packet, reads the source MAC address, source MAC address of the machine to get connected to the port;
(2) reads the destination MAC address and the corresponding port address lookup table;
(3) if the destination MAC address port, data is copied directly to this port address table;
(4) if the address table does not correspond to the destination MAC address port and broadcast to all ports, when the destination machine response, updating the address table, do not need to broadcast next;
Continuous cycle process described above, MAC address information of the entire network can learn, and thus learning switcher and maintain its address table.
MAC Layer 2 switches forward data according to the port selection algorithm is very simple, inexpensive chip that easy and fast.
Three-tier exchange
Exchange principle **: ** end to complete the data exchange in accordance with the IP address of the network layer of the third layer;
Scene: A (ip1) => three switches => B (ip2)
work process:
(1) A retransmission data to B, from B + ip address subnet mask, A and B can be determined whether they be in the same network segment;
(2.1) A and B, if the same network segment, but A does not know the MAC address B, A sends an ARP request to obtain the MAC address B, and B to the MAC transmits the data via the switcher;
(2.2) A and B, if not in the same network segment, does not know the MAC address B, A sends the packet to the gateway (A must have local MAC address of the gateway). After the gateway receives data packets, the source MAC address of the gateway will modify its own MAC address, the MAC destination IP address as the destination MAC address, in order to complete the data exchange.
The third layer switch appears to be the combination of + layer 2 switch routing function, actually not the case: the data layer 3 forwarding device, records the mapping between IP and MAC, the next time needs to be forwarded, through the first no longer three-tier equipment.
Four exchange
Two and three switching devices are based on the exchange end, this switching technique based on IP and MAC addresses, has a very high transfer rate, but the lack of dynamic data exchange function according to the purpose of the host application.
The device not only to complete the four-to-end switching, application is also possible in accordance with the characteristics of the destination host, or limit the flow distribution;
Four device based on a packet switched transport layer is based on a class of TCP / IP application layer first, the device implementing the user's application requirements;
It implements a class of application layer access control and quality assurance services, so much that it is a hardware device, as it is software NMS.
Four exchange core technology
(1) packet filtering
Use of the four information defines filtering rules, can be controlled specified port TCP / UDP communication, it may be implemented in a high-speed chip, greatly increasing the rate of packet filtering;
(2) packet priority
Only three of the following devices MAC, PORT, IP and other information, four because of lack of information and can not confirm the TCP / IP and so on four priority information;
Apparatus allows four prioritized based on the destination address / port combinations (i.e., application services).
(3) Load Balancing
The additional IP address load balancing services, the service is made by a different physical cluster, providing the same service, and defined as a single virtual server;
The virtual server is a separate logical IP server, the user data stream only flows virtual IP server, the server does not communicate with the physical;
Only by performing network address of the switch conversion (NAT), to get real access;
Virtual Server group in converting traffic to achieve a balanced, which specifically related to OSPF, RIP, VRRP and other agreements;
(4) The master backup connection
Similar to the technique (3) contained, automatic switching can be achieved with the IP standby;
Seven exchange
Exchange principle: more than four Still further, more complex may be accomplished according to the switching function in the application layer data packets (e.g., packet routing in accordance with http)
Details: multilayer switching technology
The following is taken: https: //bbs.csdn.net/topics/168097
Source: Bernardus160, the Chinese Hacker Union
There have been some initial help but hear the word confusing when switching the third layer, the fourth layer concept ensuing exchange, the seventh layer exchange is tough job faced. In fact, strictly speaking, switched connection between the source and destination addresses means that, more than any technology in the second layer can not be said to be switching technology. Load Balancing term has largely replaced the term fourth layer switching, just use the term cognitive largely replaced as the seventh layer switching. However, I am afraid that the term of the third layer switching will go on forever so called.
Of course, the argument just say, the key is to realize the benefits of these technologies to improve network performance brought on, so, we still use the term "first layers swapping" this name.
Third exchange
The third layer is also known as IP switching technology switching technology, high-speed routing technology. This is a use of the third information layer protocol switching function to strengthen mechanisms for the second layer. Most of today's enterprise networks have become an intranet implementation of TCP / IP protocol Web technology, user data is often transmitted across a local network between the Internet, therefore, routers are often overwhelmed.
One way is to install more powerful super router, however, this overhead is too large, if it is built-switched networks, such investment is clearly unreasonable. The third layer is the target exchange, as long as the second layer is a more direct path between the source and destination addresses, there is no need to forward packets through the router. Third exchange using the third layer routing protocol to determine the transmission path, this path can be used only once, it may be stored for later use. After the data packet transmitted through a virtual circuit to bypass the router quickly.
At present, the third layer switching technology are:
- Ipsilon switching the IP: IP switching technology Ipsilon initiated by the company, identification data packet stream, the second layer as far as possible in the exchange to bypass the router, improving network performance. Ipsilon improved ATM switch, the controller software deleted, plus an IP switch controller in communication with ATM switch. The technology is applicable to the in-house LAN and campus networks.
- Cisco label switching: the data packet label, the label switching node readout packet transfer route is determined. The technology is suitable for large networks and the Internet.
- 3Com Fast IP: focus on data management strategy, the principle of priority and quality of service. Fast IP protocol to ensure real-time audio or video data stream to get the desired bandwidth. Fast IP support other protocols (such as IPX), the exchange can operate in other environments in addition to ATM. The client needs to have set the priority level of the software.
- IBM ARIS (Aggregate Route-based IP Switching): Cisco label switching technology with similar numerals attached on the package, whereby through the switching network. ARIS generally used for ATM networks, may be extended to other switching technologies. The edge device entering the inlet ATM switching environment, comprising a third layer routing, the routing table is mapped to a second layer of virtual circuits. Allowing the same end of the above two ATM network computer to transmit data via a virtual circuit, thereby reducing network traffic.
- MPOA (MultiProtocol Over ATM): ATM Forum proposed a specification. By the source client request route server gives the best path routing is performed after the calculation. Then, establish a SVC, you can across subnet boundaries, do not do routing.
Currently Cisco, 3Com, Nortel, Lucent, Cabletron, Foundry and Extreme are more mature companies such as Layer 3 switching products and modules available. Below 3Com's technology, for example, to illustrate the evolution of the third layer switching technology.
The first generation of electronic switches are discrete components and software framework mixture primitive type. Function to run the software on a fixed memory of the processor, with the improvement of management support and protocol functions, software features are also increasing. When the user's daily business is more dependent on the network, increase network traffic, network equipment has become a bottleneck.
Although the processor and memory getting faster and effective, but still keep up with increased traffic levels. The first step in solving the problem is to simplify the network layer: with a substituted switch routers to reduce the overhead of packet processing and significantly improve transaction speed. 3Com are optimized for the introduction of the second layer processing application specific integrated circuit (ASIC), a 10-fold increase in performance, and reduces the overall cost of the system.
Flexible Intelligent Routing Engine (FIRE) proclaimed the advent of third-generation switching technology. This generation is not just based on the second generation of progress, but also for the third layer routing, multicast aspects (Multicast) and user-selectable policy (Policy) to provide wire-speed performance, the second and third layers performance is no longer the inconsistent.
FIRE is the third generation of the core portion of the third layer switch 3Com Corporation, which is an innovative integrated interconnection architecture that provides a wide range of function of the second and third layers, but also in a variety of rate performance on the network interface type.
The fourth layer switching
End performance and quality of service requirements for careful balancing load of all networked devices, to ensure that data between the client and the server flow smoothly. The second layer and the third layer switching products play in bandwidth and capacity to solve the problems of the local area network and the Internet a good role, but it may not be enough, you also need more performance, which is the fourth exchange comes in.
Fourth exchange technique using a third layer and a fourth layer header information to identify the application data stream session information includes TCP / User Datagram Protocol (UDP) port number, label application session start and end "SYN / FIN "bits and IP source / destination address. Using this information, the fourth layer switches can make intelligent decisions forwarded to the session where the transport stream.
For a variety of different systems to support an application of large enterprise data centers, Internet service providers or content providers, the role of the fourth floor of the exchange is particularly important. Similarly, when the copy function on many servers, the fourth layer switching will play no small role.
And a third layer switch routers when forwarding packets do not know which different data packet after which the packet in the front. The fourth layer switching technology to track and maintain the beginning to the end of each session. Therefore, the fourth layer switch is a real "conversation switch."
Routers make forwarding decisions based on availability and performance of a network link or node, and the fourth layer switches make forwarding decisions based on the session information and the application layer. Due to do this, so that the user's request can be forwarded to the "best" server according to different rules. Thus, the fourth layer is a switching technology for transmitting data over the mechanism and achieve load balancing among multiple servers of.
A fourth layer function switches can act as a "Virtual IP" is connected to the server (VIP) front end. Each server or group of servers and support a single common applications are configured a VIP address. The VIP address is sent and registered on the Domain Name System.
When issuing a service request, the determination by the fourth start of the TCP layer switch to identify the start of a session. Then it uses a complex algorithm to determine the optimum server to handle the request. Once such a decision, it will switch the session associated with a specific IP address, and use the server's IP address instead of the real VIP address on the server.
The fourth layer of each switch are stored and a server is selected to match the source IP address and a source TCP port connection table associated. The fourth layer switch then forwards the connection request to this server. All subsequent re-mapping and forwarding packets between the client and the server until the switch found so far session.
In the case of using the fourth layer switching, the access server may be connected together to truly meet the rules established by the user, such that the equal number of the access server or on each transport stream according to the capacity allocated to different servers.
The general features of a single product load balancing may be connected 400-800 per access. The connection speed (hardware-based load balancing using a custom application specific integrated circuit) of a new product while the second and fourth layers having a function is more than 100,000 times per second access.
The key issue in all of this is how to determine the transport stream to the most available server station which, at present, using a variety of methods in making load balancing decisions. The particle size required for load balancing, the fourth layer using a variety of methods can switch assigned to the server application session. These methods include simple weighted round-robin access to the minimum required number of weights, and the round-trip delay measurement server itself like a closed loop feedback.
Closed loop feedback is the most advanced method, which utilizes information specific system available memory, I / O interrupts, and CPU utilization, etc., such information may be automatically acquired as adapter driver switch and a fourth layer. The current closed loop feedback mechanism requires the installation of software agents on each server.
A fourth layer in form and function switches and dedicated load balancer completely different. Conventional hardware-based load balancing is to optimize the speed of 45Mbps two-port device.
The fourth layer switches are designed for high-speed Intranet applications that support 100Mbps or Gigabit interfaces.
In addition to load balancing fourth exchange functions also support other functions, such as the transport stream based on the control function of the application type and user ID. Multi-level queuing technique, the fourth layer may be labeled switch the transport stream and a transport stream priority is assigned according to the application. In addition, the fourth layer switches placed directly in front of the server, it is understood that the application session content and user permissions, thus making it the ideal platform to prevent unauthorized access to the server.
The fourth layer switching products
Users past surrounded them with a second layer and the third layer switch, such as switch improves the overall network throughput, making it far more than the throughput of the old technology, do not know whether this will see the fourth layer switch phenomenon.
- Berkeley Networks company exponeNT e4 and Alteon Networks company ACEswith 180 two fourth layer switching products with outstanding performance and flexibility to make more intelligent forwarding decisions than the second and third layers switch. Since the header to the switch inquiry code embedded in application specific integrated circuit (ASIC) to achieve the functions described above, hardly cause any delay. The two vendors switches can achieve 10M, 100M and Gigabit Ethernet capabilities, but Berkeley switches are designed for enterprise applications, and Alteon switch is for organizations with a large number of Web or FTP server.
- Alteon fourth layer switching technology through real-time monitoring of performance and health of a server, according to the health status of different servers, the visiting data traffic to a cost-effective manner assigned to the appropriate server. At the same time, Alteon fourth layer switching technology with a Web cache redirection function can specify the HTTP traffic destined for a remote Internet host to intercept and redirect to a local cache server these communications, which greatly speeds up access to the Internet speed, and saves a lot of valuable WAN bandwidth. And it is completely transparent to users and information providers, information providers and users do not need to do any setting.
- Cabletron's SmartSwitch Router and Torrent Networking Technologies has introduced the IP9000 Gigabit Router also has a fourth layer switching capabilities of the product. Which SmartSwitch Router can be achieved from conventional backbone third exchange to complete the third and fourth layer switching capabilities of the upgrade conversion, its unique integration capabilities and wide area network-based access control capabilities fourth layer switching network for data transmission security, orderly played a key role. In addition, Cabletron SmartSwitch Router switching function based on the fourth level QoS for a specific data exchange service application provides different levels of priority processing.
Fourth exchange scheme
In the present embodiment, to achieve load balancing of Web Server through the fourth layer of switches using Alteon.
HTTP is one of the most important Internet application, Web Server is currently widely used on the Internet, uses a multi-process technology, take up more system resources, low efficiency, generally a Web Server can only afford a few hundred concurrent users. Using L4 switch can solve the scalability problem of Web Server, Web Server system to improve the reliability and reasonable distribution of load between the Web Server.
Alteon fourth layer monitoring the availability of Web Server switches, including a physical connection, the host Web Server, HTTP Server health itself, when finding a station can not provide Web Server Web services, the Web request switch automatically assigned to two good Web Server. Alteon L4 switch can also set the maximum number of sessions per Web Server can withstand, the overflow Web Server, Web Server backup and other methods to further ensure the reliability of the Web system.
When using Web Server load balancing within the same LAN variety of load balancing algorithms, including Least Connection, Round Robin, MinMiss and Hash algorithms, as well as on weighted algorithm and so on.
When not in the same local area network within the Web Server to achieve a reasonable question for load balancing using the Global Load Balance technology Alteon switches.
The seventh layer switching
At present, especially in the high availability and load balancing, there are many advanced tools can use the information returned by the seventh layer application to the end user. These tools enable users to easily check the response and accuracy of site content, or from the customer's point of view to try measuring your site to see if there is the right applications and content.
Users can not only verify the correct transmission of content, but also to open the data packets transmitted over the network (regardless of IP address or port), and make load balancing decisions based on the information package.
Essentially, this intelligent migration beyond the function of the fourth layer. To port 80, for example, in addition to the general type of Web traffic flow, there are many types of traffic flow through this port. A fourth layer having up device function does not recognize the different types of transmission flows through the flow port, and they are treated equally so for all transport streams.
But not all the same transport stream. For load balancing products, the ability to know the data flowing through this port is still a simple request for streaming media product catalog very useful, perhaps businessmen want to give higher priority needs of clients in this directory entry. Many devices have a fourth layer function treated in the same manner as the two types of data, and thus may send streaming media data to the server can not respond, resulting in erroneous information and delay.
Seventh layer is the intelligence capable of further control, i.e. control over all transport streams and content. Since the application traffic is free to fully open / presentation layer, a careful analysis of its contents, so you can not just make more intelligent load balancing decisions based on IP and port number according to the type of application.
This can not only make a comprehensive URL-based load balancing decisions, but also to make decisions based on the actual application type, regardless of what application is using the port number. This will allow users to identify the video conference streams, and make the appropriate load balancing decisions based on this information, even though the application may be using a dynamic address allocation.
Such function has a seventh layer portion of product is to ensure recognition of different types of traffic may be given different priorities. Cognitive apparatus having a seventh layer is not dependent routing device or application to identify differentiated services (Diff-Serv), the transport stream Common Open Policy Service protocol, or other quality of service, it can be filtered transport stream and assign a priority. This allows you to not have to rely on application or network equipment to achieve these objectives.
Such standards currently seventh floor function yet. Cognitive function has the seventh layer is a highly complementary: it provides a network can co-exist with as Diff-Serv such services in harmony. It analyzes the transport stream, then it is determined, as described for the transmission of voice over IP stream requires the service provided bit, while other types of traffic only needs to set a lower priority type of service bits. "
Of course, the most important thing is the ultimate benefits of such devices can provide. In the past, we always need to balance between intelligence and speed. In the case seventh floor of cognitive technology can be made at a line speed more transport streams decision-making and intelligence. users will be free to get the information on all types of transport streams and their destination to make decisions to optimize Web access, provide better service to end users.
in summary, the seventh layer exchange data streams can achieve efficient load balancing and intelligent optimization.
The seventh layer switching products
Switches having cognitive function applications with more intelligence, analyzes the content of an input packet, the request sent to the content server or a dedicated application specific server. Using logical cluster deployment, the end user may establish a server for content and applications, network managers use these products to various embodiments a stream priority and bandwidth control. Only has a fourth layer switching functions will not be enough, fundamentally, to really provide a deeper understanding of the contents of the packet capabilities is critical.
- ArrowPoint had announced in April 1998 launched its URL has a cognitive content Web Switch CS-100 and CS-800.
- HydraWeb also launched in 1999 a program independent of load balancing equipment Hydra2500, Hydra2500 URL has both intelligence and application awareness.
- Cisco LocalDirector server by the existing characteristics of the connection management software with new features integrated, the same type of intelligence added to its exchange software, these properties will be reflected in its Catalyst product line. Cisco introduced management and troubleshooting tools Content Verification System (Content Verification System) as add-ons LocalDirector, mainly on the availability of servers and applications to query. For end users, the integrated product will be a switching device with the content of cognitive function, which means less need to manage hardware and software, in response to a request for content and applications will make more automated decision-making .
- Similar fully integrated products 3Com Corporation filed with the launch of Cisco products. 3Com plans to authorized content-based switching technology, this technology will add to F5 Networks, Inc. for the production of CoreBuilder 9000 switches. November 15, 1999, 3Com announced a positioning in e-commerce and Web hosting customers' sales reached an agreement with F5.
The industry believes that the greatest demand for more intelligent switches from running other companies in e-commerce and Web site. Another benefit of the new integrated switches is that they can eliminate the need to perform different tasks on multiple devices.
Postscript: OSI 7 layer switching technologies involved
