Comparative Analysis of Layer 3 Switches, Routers, and Hubs

As for layer 3 switches and routers, they are widely used in various fields, including hubs. The following is a detailed analysis of the differences between the three. The reason why some people are confused about the difference between layer 3 switches and routers is that layer 3 switches also have "routing" functions, which are generally consistent with the routing functions of traditional routers. Even so, there are still considerable essential differences between layer 3 switches and routers, which are introduced below.

1. Different main functions

Both the Layer 3 switch and the router have routing functions. The main function of the router is still routing, but its other functions are just additional functions. The Layer 3 switch is still a switch product, but it is a switch with some basic routing functions, and its main function is still data exchange. In other words, it has both data exchange and routing forwarding functions, but its main function is still data exchange; while the router only has the main function of routing forwarding.

2. The main applicable environment is different

Layer 3 switches are mainly used to connect simple LANs, while routers are used to connect more complex networks of various types. The routing function of a layer 3 switch is usually simpler, and the routing path is far less complex than that of a router. It is mainly used for simple LAN connections. Its main purpose in a LAN is to provide fast data exchange functions to meet the application characteristics of frequent data exchange in the LAN.

Routers are different. They are designed to meet the needs of different types of network connections. Their routing functions are more reflected in the interconnection between different types of networks, such as the connection between LAN and WAN, and the connection between networks with different protocols. Therefore, routers are mainly used between different types of networks. Its most important function is routing and forwarding. Solving the connection of various complex routing path networks is its ultimate goal. Therefore, the routing function of routers is usually very powerful. It is not only applicable to LANs with the same protocol, but also to LANs and WANs with different protocols. Its advantages lie in the functions of selecting the best route, load sharing, link backup, and exchanging routing information with other networks. In order to connect to various types of networks, routers have a wide range of interface types, while layer 3 switches generally only have LAN interfaces of the same type, which is very simple.

3. Different performance

Technically, there are obvious differences between routers and layer 3 switches in packet switching operations. Routers generally use a microprocessor-based software routing engine to perform packet switching, while layer 3 switches perform packet switching through hardware. After routing the first data stream, the layer 3 switch will generate a mapping table of MAC addresses and IP addresses. When the same data stream passes again, it will pass directly from the second layer according to this table instead of routing again, thereby eliminating the network delay caused by the router's routing selection and improving the efficiency of packet forwarding. At the same time, the routing lookup of the layer 3 switch is for data streams. It uses cache technology and can be easily implemented using ASIC technology. Therefore, it can greatly save costs and achieve fast forwarding. The forwarding of the router adopts the longest matching method, which is complex to implement and usually implemented using software, and has low forwarding efficiency.

For this reason, in terms of overall performance, the performance of a layer 3 switch is far superior to that of a router, and is very suitable for LANs with frequent data exchange; while a router, although its routing function is very powerful, its packet forwarding efficiency is far lower than that of a layer 3 switch, and is more suitable for interconnecting different types of networks where data exchange is not very frequent, such as the interconnection between a LAN and the Internet. If a router, especially a high-end router, is used in a LAN, it is a waste to a considerable extent (in terms of its powerful routing function), and it cannot well meet the communication performance requirements of the LAN.

The difference between a hub and a switch

1. A hub is a form of repeater. It works at the physical layer and, like a repeater, is often used for bidirectional forwarding of physical signals between two network nodes. It completes the functions of signal replication, adjustment, and amplification. The difference is that a hub can provide multi-port services. During the data transmission process, due to blockage, delay, and other reasons, short frames, fragments, etc. will appear. From the perspective of the ISO physical system, the hub belongs to the physical layer device. The physical layer provides a basic mechanism that encodes (sends to the physical medium) and decodes (receives from the physical medium) binary data (bits). The physical layer also defines the physical connection mechanism with the medium, but not the medium itself. Therefore, the hub only performs a single synchronization, amplification, and shaping function on the data, and cannot process short frames and fragments in the data process.

2. A switch is similar to a hub and can connect two LAN segments. It works at the data link layer and can filter frames. The switch detects the source and destination addresses of the frame. If they are in the same network segment, it will not forward them. If they are not in the same network segment, it will forward the frame to another network segment.

SWITCH works at the data link layer. This layer provides a frame consisting of information bits. The frame consists of a header or header bit containing a start flag, addressing information and (for LAN) a 32-bit cyclic redundancy code (CRC). The role of CRC is to ensure the integrity of the frame when the information bits pass through the physical medium. The data link layer also provides link management. For Ethernet, frames are transmitted when the channel is idle and stopped when a conflict is detected. In a token ring network. Frames are transmitted when a free token is received. Therefore, the switch can not only synchronize, amplify and shape the data, but also effectively filter short frames and fragments. The hub adopts a shared bandwidth working mode, while the switch has exclusive bandwidth.