Vlan Overview; Introduction To Vlan; Chapter 1 Vlan Overview - H3C S5600 Series Operation Manual

Operation Manual – VLAN
H3C S5600 Series Ethernet Switches
This chapter covers these topics:

VLAN Overview

Port-Based VLAN
Protocol-Based VLAN
1.1 VLAN Overview

1.1.1 Introduction to VLAN

The traditional Ethernet is a broadcast network, where all hosts are in the same
broadcast domain and connected with each other through hubs or switches. Hubs and
switches, which are the basic network connection devices, have limited forwarding
functions.
A hub is a physical layer device without the switching function, so it forwards the
received packet to all ports except the inbound port of the packet.
A switch is a link layer device which can forward a 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.
The above scenarios could result in the following network problems.
Large quantity of broadcast packets or unknown unicast packets may exist in a
network, wasting network resources.
A host in the network receives a lot of packets whose destination is not the host
itself, causing potential serious security problems.
Isolating broadcast domains is the solution for the above problems. The traditional way
is to use routers, which forward packets according to the destination IP address and
does not forward broadcast packets in the link layer. However, routers are expensive
and provide few ports, so they cannot split the network efficiently. Therefore, using
routers to isolate broadcast domains has many limitations.
The Virtual Local Area Network (VLAN) technology is developed for switches to control
broadcasts in LANs.
A VLAN can span multiple physical spaces. This enables hosts in a VLAN to be located
in different physical locations.
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 in the traditional Ethernet way. However, hosts in different VLANs cannot

Chapter 1 VLAN Overview

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Chapter 1 VLAN Overview