Chapter 1 Vlan Overview; Introduction To Vlan - H3C S7500 Series Operation Manual

Operation Manual – VLAN
H3C S7500 Series Ethernet Switches
This chapter covers the following topics:
VLAN Overview
Port-Based VLAN
Protocol-Based VLAN
1.1 VLAN Overview

1.1.1 Introduction to VLAN

The traditional Ethernet is a flat network, where all hosts are in the same broadcast
domain and connected with each other through hubs or switches. A hub is a physical
layer device without the switching function, so it forwards the received packet to all
ports. A switch is a link layer device which can forward the packet according to the MAC
address of the packet. However, when the switch receives a broadcast packet or an
unknown unicast packet whose MAC address is not included in the MAC address table
of the switch, it will forward the packet to all the ports except the inbound port of the
packet.
In the above scenarios, a host in the network receives a lot of packets whose
destination is not the host itself, wasting plenty of bandwidth resources and causing
potential serious security problems as well.
The traditional way of isolating broadcast domains is to use routers. However, routers
are expensive and provide few ports, so they cannot subnet the network particularly.
The Virtual Local Area Network (VLAN) technology is developed for switches to control
broadcast in LANs.
By creating VLANs in a physical LAN, you can divide the LAN into multiple logical LANs,
each of which has a broadcast domain of its own. Hosts in the same VLAN
communicate with each other as if they are in a LAN. However, hosts in different VLANs
cannot communicate with each other directly.
implementation.

Chapter 1 VLAN Overview

Figure 1-1
1-1
Chapter 1 VLAN Overview
illustrates a VLAN