【 Weak current College 】 switched routers and routing-switch

Now the router and switch between are blurring, multilayer router and switch can also implement switching and routing functionality, there are different between them? what their respective characteristics? how to select based on application requirements?

First, the traditional switches and routers

Ordinary switch work in open systems interconnection (OSI) seven-layer model of the second layer, data link layer, switching to media access control (MAC) address to be able to identify the data flow of each packet's source and a destination site's MAC address, can offer inexpensive, high-bandwidth network connection, but the ability to control packet is restricted to the broadcast domain; routers work of the OSI 7 layer model of the third layer, that is, the network layer, be able to identify the data source and destination network address control packet of capacity limited to source a destination address on the internal routing protocol, with the bulk of cacheability, usually by routing software for the interconnection between networks.

Conventional switch and router has a number of shortcomings. If the router need feature strong processors, it's great the routing table will cause a delay in a network, lead forward slow, and expensive, often become restricted network high-speed transmission bottlenecks; is located on level 2 of the ordinary switch because only read from the source MAC address for a purpose, not for a higher level of information in the packet, thus switching function is limited to the main data stream does not have the necessary control.

Second, the third layer switching and Routing switches

The third Exchange with wire-speed switching technology, the exchange rate reaches a transmission line on the data transfer rate, eliminates exchange bottleneck. Achieve wire-speed switching of the key role of hardware (a special-purpose processor) instead of traditional software implementation protocol analysis and packet forwarding. Wire-speed switching is designed to be simple, high reliability, low power consumption, feature many advantages. Wire-speed switching of implementation also depends on distributed processing technology, it can also handle multiple ports for data streams. So the third Exchange in General is the central processing unit (CPU), reduced instruction set computer (RISC), application specific integrated circuit (ASIC) and parallel processing system.

Use the third Exchange technology, while the integration section for routing function switches are layer 3 switch or router switch. It preserves a third layer of network topology and services, these structures and services in Internet, security, manageability, and broadcasting, and other aspects of great advantages, with the identification of a variety of application layer protocols, can contribute to the achievement of the policy-based control network.

Routing switches have higher routing capacity and lower latency, can simultaneously support network protocol (IP) and IPX, have some security mechanisms, such as access control, etc. However, lack of router routing switches, and the flexibility of the support only a limited number of routing protocols, but also lack the ability to cache the advanced router.

Third, the fourth level of Exchange and switching routers

On the network every time access is in the client and the server generates a series of packets that the packet data stream can be composed of, respectively, in the second, third or fourth floor to be identified, each layer in turn provides the data stream and more detailed information. Network management of one of the most basic job is to control the network data flow. If a client while using the same server for multiple applications, then simply read the third layer of information will not be aware that on the same server has many different applications in use, so you can't argue the flow of data from different applications to recognize, even not for each data flow through the implementation of different targeted control rules.

Routing switches (Layer 3 switch) integrated switching and routing capability, resulting in layer 2 switching and routing functions, solves the traditional router in the performance of certain shortcomings. But it does not complete all of the routing functionality, nor will it be available in the application layer provides data flow control.

Obviously, if you want to combine packet forwarding performance and data flow control feature, you must further in the network of the fourth level of recognition stream. The OSI model of the fourth floor is the transport layer, it is responsible for coordinating network source and purpose of the communication between systems. Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are located on the fourth floor, their header contains a port number, the port number to identify each package contains application protocols, such as port number 21 for file transfer protocol (FTP), port 80 for Hypertext Transfer Protocol (HTTP), and so on. So identify the fourth floor and have access to every packet in the application of some of the information.

The fourth layer header port number information and third-tier header source objective information, allows the client and server for different applications achieve more precise control, if switching router is a full-featured, all these tasks can be completed at wire-speed, and can implement a variety of control, this switch is called switched router.

Exchange queries for the Gondo router and control functions are implemented through hardware ASIC. ASIC can be collected on the first packet flow of information, the more you can act on the packet flow control level is more accurate. A client/server can simultaneously several different application session, and a corporate backbone can exist thousands of client/server pair, so a backbone-class switching router must have a very large table capacity to store up to hundreds of fourth layer information. Routing Switch generally does not have enough saved for a fourth-tier dataflow information of large-capacity buffer.

IV. advantages of switching routers

Switched router with 4-layer switching capabilities, you can read the fourth level of header information, since the fourth level of TCP and UDP header contains the port number to identify each package contains the application protocol, thus switching routers may be concluded in the fourth level of control functions, this will bring many benefits.

1-needleOn the applications more reasonable service quality policy

Genuine quality of service (QOS) policies should be able to provide to all applications at wire speed bandwidth and low latency, meet all the traffic on the network. When the switch occurs one output port as well as the internal buffer is overload is full, the quality of services should have priority rules to prioritize network traffic.

Switching routers allow for application layer flow set service quality policy to use the network managers on the backbone bandwidth use for full control. In the second and fourth layer switching, QoS policy can only be controlled based on the source of a destination address of the network traffic. On the fourth floor use different application service quality policy, it means that the individual client and host applications dialogue also will be able to set priorities, this QoS policy is more reasonable and more comprehensive.

2, based on application layer flexible, efficient network security measures

Traditional router for the corporate network and the database's security needs, use the security filters and access control list control different access implementation. Based on the software causing a consequence is that once you have enabled security transition, central processor in each packet of directives need to be performed on greatly increase, resulting in a significant decline in the performance of the router, for example, in some router sets a DNS filter will probably degrade performance by 70 percent.

But switched router and security characteristics for the performance loss is small, when including security, advanced feature is activated, switched router also provides wire-speed performance. In switched routers, the packet is in a particular ASIC for processing, as captured by the source and destination port information, application-layer security and wire-speed performance is possible. For example, a network administrator can according to user's application to control user access to company information, rather than prohibit all users from accessing a particular application. This allows network administrators have more flexibility and better for the corporate network's control, and makes the desktop can choose to use more applications.

3. application-specific information for perfect flow

Management measurement is an important part of the network management, you cannot measure network traffic will not be able to implement effective management of the network, by tracking the application flow, switching router improves flow measurement, accounting and performance monitoring capabilities.

Billing information is directly converted to a standard port of RMON/RMON2, do not need to use a separate external RMON/RMON2 probes. Thus, switching routers will always be able to provide wire-speed on all ports RMON/RMON2 (including all functional groups), and managers are able to directly access the switched router RMON/RMON2, statistical data.

Detailed accounting enables network managers to understand which applications are massive consumption of bandwidth in order to balance the load between servers. For the Internet service provider (ISP), such a detailed accounting characteristics enable them to provide a copy of the "phone bill" and specify a per-user applications and bandwidth.

5. Summary

Network application development to promote the progress of the network devices, layer 3 switch although resolving IP/IPX routing performance and price, but in the application flow of recognition and control was not satisfactory. Switched router solves this problem by using advanced ASIC technology, with hardware directly handle the fourth tier dataflow. Switching routers have the following advantages: even in the peak period of network use, or available through the application level QoS policy to guarantees intelligent switching routers provide ideal performance; detailed port traffic statistics you can quickly and easily troubleshoot network problems; to ensure the security of main link, wire-speed access control ensures the stability of the network performance.

Now many companies of intelligent switching routers are able to provide all port Gigabit per second rate for the second, third and fourth layer switching functionality, high speed dedicated ASIC chip packets through to the second, third and fourth layer header look for packet forwarding. In addition, intelligent switching routers can be passed in the fourth level of Exchange packets for a bandwidth allocation, failed assertions and for TCP/IP applications stream access control, and provides detailed traffic statistics and accounting information, as well as application-level QOS policies and access control capabilities.

Although switched router by ASIC significantly improves its performance and functionality, but dynamic routing table update processing is still based on the software. The initial switching routers only supports router information Protocol (RIP), for a simple network, RIP is usually sufficient, but a large network of backbone switched router requires support open shortest path first (OSPF) routing protocol, and other more complex routing protocol.

Recently, with the multicast (Multicast) applications increasingly popular, switched router should implement full standards-based protocol for multiple group pulling, this includes the support of various routing protocols, such as distance vector multicast routing protocol (DVMRP) and more scalable and Protocol-Independent Multicast Protocol (PM).