Basics of In-Vehicle Ethernet Switches: What is an L2 SWITCHES?

An L2 SWITCHES is SWITCHES that configures the smallest unit of a network. The smallest unit is a network configured based on the "Data Link Layer" defined in Layer 2 of the OSI reference model. L2 SWITCHES forward and control FRAMES (packets) and play a role in efficiently facilitating communication between devices within the network. This page explains the functions and features of L2 SWITCHES.

L2 SWITCHES learn the MAC addresses of connected devices. These learned addresses are recorded in an internal database called the MAC address table. The MAC address table is used to determine where to forward FRAMES. SWITCHES updates the MAC address table every time FRAMES arrives, learning the MAC addresses of new devices.

L2 SWITCHES refer to FRAMES 's destination MAC address and forward FRAMES to the appropriate port. Because MAC addresses are unique to each device, FRAMES are delivered directly to the destination device and are not forwarded to other ports. This minimizes network traffic and improves communication efficiency.

L2 SWITCHES support virtual LANs (VLANs). VLANs are used to logically divide a physical network and control communication between different segments. L2 SWITCHES support multiple VLANs and create independent groups (broadcast domains) for each VLAN.
They also contribute to improving network performance by creating broadcast domains. Broadcast FRAMES are forwarded to all devices on the network, which can increase network traffic. When an L2 SWITCHES receives a broadcast FRAMES, it does not forward it to other ports, but only to devices within the same segment. This controls the impact of broadcast FRAMES and improves network performance.

VLAN (Virtual LAN) is a technology that creates individual network environments by virtually dividing or combining physically connected networks. Multiple ECUs are connected to an in-vehicle Ethernet switch, but VLAN allows ECUs to be grouped together and communication to occur only within that group.
Since networks separated by VLANs are independent networks, communication between networks is not possible using an L2 SWITCHES, and an L3 SWITCHES or router is required.

A trunk port is a port used when configuring multiple VLANs using multiple SWITCHES. To transfer FRAMES between multiple VLANs, a VLAN tag is used to identify FRAMES. This allows network devices to forward FRAMES to the correct VLAN, and the receiving device to receive FRAMES of the correct VLAN. Without a trunk port...
When configuring multiple VLANs on multiple SWITCHES, the number of SWITCHES ports is consumed by the number of VLANs. With a trunk port, this can be completed with one port (one CABLES, so it can also be said to be a port that belongs to multiple VLANs.