How layer-3 switches work

As we all know, layer-3 switches are suitable for some small local networks and small and medium enterprises. This does not need to be described too much here. Next we will introduce the layer-3 switch technology to you, I believe this is something that many users can use in their daily lives.

The layer-3 Switch establishes a ing between the address and the switch port based on the source MAC address in the received data frame, and writes it to the MAC address table. The switch compares the destination MAC address in the data frame with the created MAC address table to determine which port is used for forwarding.
　
If the destination MAC address in the data frame is not in the MAC address table, it is forwarded to all ports. This process is called flood. Broadcast frames and multicast frames are forwarded to all ports. Learning: the Ethernet switch understands the MAC address of each port connected device, and maps the address with the corresponding port and stores it in the MAC address table in the switch cache.

Forwarding/filtering: when the destination address of a data frame is mapped to a MAC address table, it is forwarded to the port connecting to the target node instead of all ports. If the data frame is broadcast or multicast frame, it is forwarded to all ports ). Eliminate loop: When a vswitch includes a redundant loop, the Ethernet switch avoids loop generation through the Spanning Tree Protocol and allows a backup path.

The CIDR Block connected to each port of a layer-3 switch is an independent conflict domain. The devices connected to a vswitch are still in the same broadcast domain. That is to say, the only exception to a vswitch that is not isolated from a broadcast is in a VLAN environment ).

A vswitch forwards data based on the frame header. Therefore, a vswitch is a network device on the data link layer. The vswitch mentioned here only refers to a traditional L2 switching device ). According to the different operation modes when the switch processes frames, there are two main types:

Storage forwarding: before forwarding, the switch must receive the entire frame and perform error checking. If there is no error, the frame is sent to the destination address. The forwarding latency of frames passing through a vswitch varies with the frame length. Pass-through: the switch immediately forwards the frame as long as it detects the target address contained in the frame header, without waiting for all the frames to be received or performing error verification. Because the length of the Ethernet frame header is always fixed, the forwarding latency of frames through the switch remains unchanged.

L2 switches are also called bridging) hardware-based bridging. Forward data packets based on the unique MAC address of each end site. The high performance of layer-2 switching can generate a network design that increases the number of hosts in each subnet. It still has the characteristics and restrictions of bridging.

Layer-3 switching is based on hardware routing. The main difference between a vro and a layer-3 vswitch in Packet Exchange Operations is physical implementation. A simple definition of layer-4 switching is not only based on layer-2 bridging of MAC) or layer-3 routing selection of source/destination IP addresses ).

It also makes forwarding decisions based on TCP/UDP application ports. This allows the network to differentiate applications when determining routes. Data streams can be prioritized based on specific applications. It provides more detailed solutions for Policy-based service quality technologies. Provides a method to differentiate application types.

L2 switching technology has been widely used in LAN construction and transformation from bridging to VLAN Virtual LAN. Layer 2 switching technology is the Layer 2 that works in the OSI Layer 7 network model, that is, the data link layer. It forwards data according to the target MAC address of the received data packet, which is transparent to the network layer or high-level protocols.

It does not process IP addresses at the network layer, but does not process port addresses such as TCP and UDP of high-level protocols. It only needs the physical address of the data packet, that is, the MAC address. Data Exchange is implemented by hardware, its speed is quite fast, which is a significant advantage of L2 switching.

However, it cannot process data exchange between subnets of different IP addresses. A traditional router can process a large number of packets that span the IP subnet, but its forwarding efficiency is lower than that of Layer 2. Therefore, to use the advantage of Layer 2 forwarding efficiency, it must process Layer 3 IP packets, the layer-3 exchange technology was born.

Working principle of layer-3 Switching Technology

Layer-3 switching is the layer-3 (Network Layer) in the OSI Layer-7 network model. It uses the IP packet header information in the layer-3 protocol to mark subsequent data business flows, subsequent packets with the same mark of business flow are exchanged to the second layer data link layer.

This allows you to access a path between the source IP address and the destination IP address. This path goes through the second link layer. With this channel, the layer-3 switch does not need to split the received packets to determine the route. Instead, it directly forwards the packets and exchanges the data streams.

In recent years, three-layer technology has been widely promoted, and many people have shouted three-layer technology. Some people say this is a very new technology. Some people also say that it is a three-layer exchange technology, there is no new things in the stack of routers and L2 switches. Is that true? Next, let's take a look at the working process of a layer-3 Switch through a simple network.

1. Correct Interpretation and test of vswitch Port
2. Summarize the market status of high-end Switches
3. Focuses on core layer switch faults
4. PythonAndroid
5. Let's talk about the stacking of Ethernet switches.