Describe the clever development of layer-3 Exchange Technology

Describe the clever advantages and circumvent weaknesses of the layer-3 exchange technology. The layer-3 Exchange Technology is currently a very popular technology. What characteristics does it have? In the exchange network environment, user information is transmitted only between the source node and the target node, and other nodes are invisible.

Layer 3 Exchange Technology

The introduction of LAN switches enables dedicated bandwidth between network sites, eliminating unnecessary Collision Detection and error re-transmission, and improving transmission efficiency, several independent communication processes can be maintained in parallel in the vswitch. In the exchange network environment, user information is transmitted only between the source node and the target node, and other nodes are invisible.

However, when a node sends a broadcast or multicast packet online, or a node sends a MAC address packet that the switch does not know, all nodes on the vswitch will receive this broadcast message. The entire exchange environment constitutes a large broadcast domain. Point-to-point is a fast and effective exchange on the second layer. However, broadcast storms can compromise network efficiency.

Vswitches are much faster and cheaper than vrouters. It can be said that in the network system integration technology, the first-layer interface and the second-layer exchange technology that are directly oriented to users have obtained satisfactory answers. The exchange LAN technology enables dedicated bandwidth to be exclusive to users, greatly improving the efficiency of LAN transmission.

However, layer-2 switching also exposes vulnerabilities that cannot be effectively solved by broadcast storms, inter-network interconnection, and security control. As the core of the network, the router technology that acts as the interconnection between networks has no qualitative breakthrough. Most of today's enterprise networks have become the Intranets of Web technologies that implement TCP/IP protocols. User data is often transmitted across the local network over the Internet, so routers are often overwhelmed.

Traditional routers are software-based and have complex protocols. Compared with lan speed, their data transmission efficiency is low. At the same time, it serves as the hub for interconnection between network segments (subnets and VLANs), which makes traditional router technologies face severe challenges. With the rapid development of Internet/Intranet and the wide application of B/S (Browser/Server) computing modes.

Cross-region and cross-network business is growing rapidly, and the industry and users are deeply aware of the bottleneck effect of traditional routers in the network. It is imperative to improve the traditional routing technology. One way is to install a super router with higher performance. However, this is too costly. If it is to build an exchange network, this investment is obviously unreasonable.

In this case, a new routing technology came into being. This is the layer-3 switching technology, also known as IP exchange technology and high-speed routing technology. The third layer exchange technology is proposed in contrast to the traditional exchange concept. As we all know, the traditional exchange technology operates on the Layer 2-data link layer in the OSI Standard network model, the layer-3 switching technology implements high-speed packet forwarding in the network model.

Simply put, layer-3 exchange technology is layer-2 exchange technology + layer-3 forwarding technology. This is a mechanism that uses information in the layer-3 protocol to enhance the layer-2 exchange function. A device with layer-3 switching is a layer-2 switch with layer-3 routing, but it is an organic combination of the two, it is not simply to overlay the hardware and software of the router device on the LAN switch.

From the hardware implementation point of view, at present, the interface modules of the second layer switch exchange data through the High-Speed Backplane/bus (the speed can reach dozens of Gbit/s, in layer-3 vswitches, layer-3 router-related Routing hardware modules are also inserted on the high-speed backplane/bus.

In this way, the routing module can exchange data with other modules to be routed at a high speed, this breaks through the speed limit of the traditional external router interface (10 Mbit/s --- 100 Mbit/s ). In terms of software, layer-3 switches also have major initiatives. They define traditional software-based router software. The practice is:

For data packet forwarding, such as IP/IPX packet forwarding, these regular processes are implemented through hardware at high speed. For layer-3 routing software, such as route information update, route table maintenance, route calculation, and route determination, Use optimized and efficient software.

Assume that two sites using the IP protocol communicate with each other through the layer-3 Switch. When sending Site A, the IP address of the destination site is known, however, you do not know the MAC address required to send messages on the LAN. IP Address Resolution (ARP) is used to determine the MAC address of the target site.

The sending station compares its IP address with the IP address of the destination station, and extracts the network address using the subnet mask configured in the software to determine whether the destination station is in the same subnet as itself. If the destination site B and the sender Station A are in the same subnet, A broadcasts an ARP request, and B returns its MAC address, after obtaining the MAC address of the target site B, A caches the address and uses the MAC address to package and forward data. The second layer switch module looks for the MAC address table to determine whether to send data packets to the target port.

If two sites are not in the same subnet, if Station A needs to communicate with Station C, station A must send an ARP (Address Resolution) packet to the "Default Gateway, the IP address of the "Default Gateway" has been set in the system software. This IP address actually corresponds to the layer-3 Switch module of the layer-3 switch.

Therefore, when the sender station A broadcasted an ARP request to the IP address of the "Default Gateway", if the layer-3 switching module obtains the MAC address of the destination station B in the previous communication process, then, send A reply to the MAC address of B. Otherwise, the layer-3 Switch module broadcasts an ARP request to the target site based on the route information.

After receiving the ARP request, the target Station C replies to the MAC address of the layer-3 Switch module. The layer-3 Switch module saves the address and replies to the sending station. Later, when packet forwarding between A and C is performed, the MAC address packet of the destination site will be used, and the data forwarding process will be handed over to the second layer for exchange, so that information can be exchanged at A high speed.

Layer-3 switching has the following outstanding features:

◆ The combination of organic hardware accelerates data exchange;

◆ Optimized routing software improves the routing efficiency;

◆ In addition to necessary route decision processes, most data forwarding processes are processed by Layer 2 switching;

◆ When multiple subnets are connected, they are only logically connected to the layer-3 Switching Module. Unlike traditional external routers, ports need to be added to protect users' investment.

The goal of layer-3 switching is that as long as there is a more direct layer-2 channel between the source address and the destination address, there is no need to forward data packets through the router. The layer-3 Switch uses the layer-3 routing protocol to determine the transfer path, which can be used only once or stored for future use.

Then, data packets are quickly sent through a virtual circuit bypass the router. The emergence of layer-3 switching technology solves the problem that the subnet must be managed by routers after the network segments are divided in the LAN, and solves the network bottleneck caused by the low speed and complexity of traditional routers. Of course, the layer-3 switching technology is not a simple superposition of network switches and routers, but an organic combination of the two to form an integrated and complete solution.

The limitations imposed by the traditional network structure on user applications are the key issues to be addressed by the layer-3 switching technology. Currently, the maximum processing capacity of the most advanced vrouters on the market is 0.25 million packets per second, while the maximum processing capacity of the most advanced vswitches is more than 10 million packets per second. The difference between the two is 40 times.

In a switching network, especially a large-scale switching network, it is unimaginable to have no routing function. However, the processing capability of the router limits the speed of the switching network, which is the problem to be solved by layer-3 switching. Layer-3 switches do not spread broadcast packets like other layer-2 switches. layer-3 switches are called layer-3 switches because they can understand layer-3 information, such as IP addresses and ARP.

Therefore, a layer-3 switch can understand the purpose of a broadcast packet, and meet the needs of the people who send the broadcast packet without spreading it out, (whether they are in any subnet ). If the layer-3 switch is a router, it should also be called a super-high-speed anti-traditional router, because the layer-3 switch does not perform any "split" data packets, all packets passing by will not be modified and will be transferred to the destination at the exchange speed.

At present, there is still a long way to mature layer-3 switches. Like some other new technologies, it is still necessary to standardize their protocols. At present, many manufacturers claim to have developed third-tier switches. However, they have been tested by international authorities with different practices and different performance. In addition, it may be based on the strategy of various manufacturers occupying the market. Currently, layer-3 switches can exchange routing IP addresses/IPX protocols, and cannot handle other dedicated protocols with certain application fields.

Therefore, relevant experts believe that layer-3 exchange technology will be the main network integration technology in the future. Traditional routers will be applied within a period of time, but they will be in the position they can do, that is, Wan interconnection, security control (firewall), and heterogeneous network interconnection with dedicated protocols at the edge of the network.