What is the relationship between routing and layer 3 switches?

LAN split and IP inter -communication

　For Ethernet communication, data is sent and received in a unit called a frame.At the top of the frame, the MAC address of both the destination and the source is stored, which delivers data to the correct opponent.

　Therefore, a computer that communicates must first know the opponent's MAC address.For this reason, a broad cast frame is used.If you send a broad -cast frame, such as "My telecommunications partner should reply to the MAC address," all computers in the LAN will receive the frame and reply to the MAC address.This allows you to communicate with the correct partner.

　しかし、大量のブロードキャストフレームが流れると、コンピュータはそれに処理能力を奪われてしまう。これを「ブロードキャストストーム」と呼ぶ。経験的に、ブロードキャストフレームはLAN内のコンピュータの数の二乗に比例して増えることが知られている。そのため、LANに接続されるコンピュータが一定数を超えると、LANの分割が行なわれる（図1）。100台が接続された1つのLANを、50台ずつの2つのLANに分割してブロードキャストドメインを小さくする、といった具合だ。しかし、LANを複数のセグメント^※1に分割するだけでは、別々のセグメントに振り分けられたコンピュータ間の通信ができなくなってしまう。

Figure 1 Divide the broad cast domain

　Therefore, the IP is located at the top of Ethernet.Ethernet identifies the communication partner using a hardware assigned MAC address (= physical address), but identifies with a software assigned IP address (= logical address).IP addresses are also assigned based on unified rules around the world, and in principle not overlapping.In addition, the communication data of the IP is separated into a unit called "packet" and is transmitted and received.Then, in a large network, use a device called "router" to divide the Ethernet broad -cast domain to perform "forward (transfer) processing" of the necessary packets.

(Next page, following "IP address and routing")