VLAN(Virtual LAN)

VLAN (Virtual LAN) is a technology for dividing a network with Layer 2 switches. By using VLANs on Layer 2 switches to divide the network, the logical configuration of the network can be freely decided. In addition, VLANs are not used only with Layer 2/Layer 3 switches. It is also the VLAN settings that determine how virtual servers are connected to the network.

The need to divide the network

VLAN allow Layer 2 switches to divide an Ethernet network. In this article, I will explain in detail about "Why do we need to divide the network?

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VLAN Overview

This section summarizes the features of VLAN. In particular, you should have a clear understanding of the implications of VLAN for improving security.

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VLAN behavior

The VLAN is very simple. It divides the network by "forwarding Ethernet frames only between ports of the same VLAN".

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Access port : Port assigned to only one VLAN

There are two types of ports on a switch: access ports and trunk ports, depending on how the ports and VLANs are assigned. This section explains access ports in detail.

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Trunk port : Port assigned to multiple VLANs

A trunk port is a port that can be assigned to multiple VLANs. When you want to create VLANs across switches, it is efficient to use trunk ports to connect between switches.

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Summary of Trunk Protocols - IEEE802.1Q and ISL

IEEE802.1Q and ISL are trunk protocols to which VLAN information is added when Ethernet frames are forwarded over trunk links.
This section describes the IEEE802.1Q and ISL formats.

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Native VLAN

Ethernet frames with native VLANs do not have a VLAN tag added when they are forwarded over the trunk. This section explains how native VLANs work.

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Cisco DTP

Cisco Catalyst switches can automatically determine the trunk port/access port according to the opposite port with DTP (Dynamic Trunking Protocol).

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Cisco Configuring and Verifying VLAN

This section describes how to configure and verify VLANs in Cisco.
Let's imagine how VLANs and ports are connected inside the switch by VLAN configuration.

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Voice VLAN - VLAN for connecting IP phones

By configuring Voice VLAN, IP phones can be efficiently connected to the corporate network.
This section explains in detail how Voice VLAN works and the configuration commands.

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Inter VLAN routing overview

When Layer 2 switches divide a network by VLANs, communication between VLANs becomes impossible, and inter-VLAN routing is used to interconnect VLANs and enable communication between them.

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Inter-VLAN routing by router

This section is about inter-VLAN routing using routers. There are two ways to connect a router and a Layer 2 switch, one with multiple links per VLAN and the other with a single link.

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Inter-VLAN routing by Layer 3 switch

In order to interconnect VLANs (networks) with Layer 3 switches, it is important to know how to configure IP addresses.
There are two ways to configure an IP address on a Layer 3 switch.

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Configuring and Verifying Inter-VLAN Routing by Cisco Router

CiscoルータとCatalystスイッチでのVLAN間ルーティングの設定についてです。シンプルなネットワーク構成での具体的な設定例と確認のshowコマンドのログでVLAN間ルーティングの理解を深めましょう。

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Cisco Configuring Inter-VLAN routing by Layer3 switch : SVI/routed port

This is the configuration of a Layer 3 switch in Cisco, where the VLAN (network) is connected by configuring the IP address on the SVI or routed port.

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