Basic principles and design ideas of layer-3 switches

Layer-3 switches are quite common, so I have studied the basic principles and design ideas of the layer-3 switches. I will share them with you here, hoping they will be useful to you. Based on the introduction of the three-layer switch technology and the working principle of the three-layer switch, the design of a three-layer switch is given. According to the design, the three-layer switch has been put into operation.

1. Introduction traditional routers work in isolated networks, isolated broadcasts, route forwarding, and firewalls. With the continuous development of the network, the load of routers also increases rapidly. One of the important reasons is that VLAN Virtual LAN technology is widely used in networks for security and management convenience. VLAN technology can logically isolate different network segments, ports, and even hosts. Communication between different VLANs must be forwarded through routers. Because of the large data traffic in the LAN, a large amount of information exchange between VLANs must be forwarded through routers. At this time, as the data traffic increases, routers become the bottleneck of the network. To solve the bottleneck of the local area network, many enterprises use layer-3 switches to build local areas in their internal, school, and residential areas. The layer-3 switch technology introduces the switching technology to the network layer. The applications of the layer-3 Switch also penetrate into the access layer of the network edge from the backbone layer and convergence layer of the original network center.

2. layer-3 Exchange Technology

2.1 The concept of layer-3 switching, also known as IP exchange or high-speed routing, is proposed in contrast to the concept of traditional switching. 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. To put it simply, the layer-3 exchange technology is the layer-2 exchange technology + the layer-3 forwarding technology. This is a mechanism that uses the 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 a router device on a LAN switch.

In terms of hardware implementation, the interface modules of Layer 2 switches exchange data through high-speed backplane/bus. In layer-3 vswitches, layer-3 router-related Routing hardware modules are also inserted on the high-speed backplane/bus, this method enables the routing module to exchange data with other modules to be routed at a high speed, thus breaking the speed limit of the traditional external router interface by 10 Mbit/s-100 Mbit/s ). In terms of software, layer-3 switches redefine traditional software-based routers:

1) Data Packet forwarding: for example, IP/IPX packet forwarding, these regular processes are implemented through high-speed hardware;

2) layer-3 routing software: such as route information update, route table maintenance, route computing, route determination, and other functions, which are implemented with optimized and efficient software.

Assume that there are two sites that use the IP protocol, and the communication process through the layer-3 switch is: if the sending Site A knows the IP address of the destination site B when it starts sending, but it does not know the MAC address it needs to send on the LAN, it needs to use address resolution ARP) to determine the MAC address of B. A compares its own IP address with B's IP address, uses the subnet mask configured in its software to extract the network address to determine whether B is in the same subnet as itself. If B and A are in the same subnet, A broadcasts an ARP request, B returns its MAC address. A obtains the MAC address of B and caches the address, use this MAC address to package and forward the data. The second layer switch module looks for the MAC address table and determines to send the data packet to the destination port. If the two sites are not in the same subnet, A sends an ARP Address Resolution packet to the "Default Gateway", and the IP address of the "Default Gateway" is already set in the system software, this IP address actually corresponds to the layer-3 Switch module of the layer-3 switch. When A broadcasted an ARP request to the IP address of the "Default Gateway", if the layer-3 Switch module obtains the MAC address of B in the previous communication process, then, send A reply to the MAC address of B to the sender. Otherwise, the layer-3 Switch module broadcasts an ARP request to the destination based on the route information, B receives the ARP request and 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 is performed between A and B, the MAC address packet of the destination site will be used. The data forwarding process will be handed over to the second layer for exchange processing, information can be exchanged at a high speed. The third layer of information exchange features the following:

1 ). The combination of organic hardware accelerates data exchange;

2 ). The optimized routing software improves the routing efficiency;

3 ). In addition to the necessary route decision processes, most data forwarding processes are processed by Layer 2 exchange;

4 ). 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.

3. In consideration of market needs, switch costs, and proprietary intellectual property rights, the design of a layer-3 Switch has developed the VLSW4150 series switch with proprietary intellectual property rights. VLSW4150 series switches are a high-performance, multi-layered solution for enterprises. VLSW 4150 is also applicable to ISP and service providers, especially for some large carriers, which will be able to enhance their competitiveness in the IP market.

3.1 overall design the VLSW4150 switch has 24 RJ45 10/100 BASE-TX adaptive ports and provides two optional Optical Fiber 10/100 BaseTx Ethernet ports, 100BaseFx Fast Ethernet ports, or Gigabit Ethernet ports SX, LX, ZX ), in addition, a serial port and a M Ethernet port are provided to configure the switch.

The architecture of the VLSW4150 switch supports a maximum rate of 11 Gbps and a multi-layer switching rate of 6.6 Mpps. It supports 8,192 MAC addresses. To better control network traffic and network security, it also supports 1 Mbit/s as the step speed limit. It also supports TaggedVLAN and MAC-based frame Filtering, as well as RIP, OSPF, and BGP routing protocols.

The VLSW4150 switch provides stack technology to manage multiple switches with one logical IP address, mirror other data packets on one port, and provide a Web-based network management system and CLI to debug the switch. VLSW4150 supports SNMP, RMON, and Telnet for ease of management.

3.2 Hardware Structure

The hardware structure of the VLSW4150 layer-3 switch is divided into two parts: the processor module and the switch module, which are connected through the PCI interface and form a complete layer-3 switch system with the corresponding peripheral circuit.

1) processor module

The processor uses a pair of lapowerquicciicpu. The same external storage device and some peripheral circuits constitute the processor part of the layer-3 switch. The processor module is mainly used to run the embedded operating system and maintain the system and route table, rather than the components of the data forwarding path. The CPLD saves some CPU initialization configurations to ensure that the CPU starts up properly after power-on. The Flash chip is used to store all the software and related configurations required for layer-3 switches, after the system is started, the SDRAM is loaded into the FLASH program to ensure the normal operation of the system. The processor module provides a fast Ethernet interface and an asynchronous port for configuring and debugging the switch. On the other hand, it connects to the switch module through the PCI interface and controls the switch module through the PCI interface, and data transmission.

2) Switch Module

The switch module uses the BCM5645 of BROADCOM as the ASIC chip, communicates with the processor module through the PCI interface, and uses the memory interface provided by 5645, the switch module can be provided with a 64 m external SDRAM, which improves the throughput and switching speed of the switch. 5645 use the MII interface and GMII interface to connect 24 Mbps Ethernet and 2 Gigabit Ethernet respectively.

3.3 Software Structure

The software system of the VLSW4150 layer-3 Switch adopts a modular and distributed design method based on the real-time multi-task operating system. The structure of the software system is hierarchical. One layer is built on the other layer, and each layer uses the services provided by the next layer of the nearest neighbor, in addition, it provides a higher level of service for the above layer. Its advantage is that it can shield the underlying operations from the software on the upper layer, improve the portability of the upper layer software, and improve the maintainability of the software. The software is divided into three layers:

1) driver layer

The driver connects the upper-layer software with the hardware system, and changes the route update, management, and configuration commands of the Upper-layer software into the format that the hardware system can recognize, to update its internal data structures, such as route tables and address tables, and control and manage the hardware exchange system; at the same time, the device driver transmits the route update packets received by the underlying hardware, control management frames, and various received information to the upper-layer software for processing;

2) protocol stack

Implements TCP/IP, 802.1D, and 802.1Q protocols to provide good interfaces for upper-layer applications;

3) Application Layer

The main modules include the routing module and network management module. The routing module implements the RIP and OSPF protocols to implement the main functions of layer-3 routing. The Network Management Module implements network management modules such as SNMP and RMON, the layer-3 Switch has some network management functions to ensure better normal operation of the layer-3 switch.

4. layer-3 Switch Application

The primary purpose of a layer-3 switch is to replace a traditional router as the core of the network. Therefore, any vro that does not require wide-area connection and requires a router can be replaced by a layer-3 switch. In Enterprise Networks and campus networks, layer-3 switches are generally used in the core layer of the network, and different subnets or VLANs are connected using layer-3 switches with Gigabit ports or MB ports. the layer-3 Switch solves the problem that LAN VLANs must be managed by routers and network bottlenecks caused by low speed and complexity of traditional routers. Using a layer-3 Switch to divide VLANs in a LAN can meet the needs of Multiple Flexible logic combinations on the user end, preventing the generation of broadcast storms. Different access permissions can be set for different VLANs as needed, this increases the overall security of the network and greatly improves the efficiency of network administrators. In addition, layer-3 switches can reasonably configure information resources, reduce network configuration costs, and make the connections between switches more flexible.