3com 3031 Instruccion De Instalación
20
VLAN C
ONFIGURATION
Introduction to VLAN
Ethernet is a kind of data network communication technology, which is based on
the shared communication medium of CSMA/CD (Carrier Sense Multiple Access
with Collision Detection). Under CSMA/CD, each node will use the shared medium
to send out frames in turn. Thus, in one moment, only one host can send out
frames while other hosts can only receive frames.
the shared communication medium of CSMA/CD (Carrier Sense Multiple Access
with Collision Detection). Under CSMA/CD, each node will use the shared medium
to send out frames in turn. Thus, in one moment, only one host can send out
frames while other hosts can only receive frames.
When many hosts are connected to the hub (with star architecture) through the
twisted pairs, or connected together by the coaxial cables (with bus architecture),
all the hosts interconnected to the shared physical media forms a physically
collision domain, which is usually considered as a LAN segmentation. According
to the Ethernet principles mentioned above, it can be concluded that the
following problem exists on connecting LAN through hub: excessive hosts can
cause severe collision, broadcast storm and affect the performance of the net or
even make the net unusable.
twisted pairs, or connected together by the coaxial cables (with bus architecture),
all the hosts interconnected to the shared physical media forms a physically
collision domain, which is usually considered as a LAN segmentation. According
to the Ethernet principles mentioned above, it can be concluded that the
following problem exists on connecting LAN through hub: excessive hosts can
cause severe collision, broadcast storm and affect the performance of the net or
even make the net unusable.
The above problems can be solved by using the Transparent Bridge or LAN Switch
to interconnect the LANs. The switch establishes a MAC-PORT mapping table with
the source MAC addresses of frames received. For the received data frames, the
switch will look up their destination MAC address in the mapping table. If it can
find the destination MAC address, the switch will send the frame only to the port
corresponding to the address, or if it cannot find the destination MAC address, the
switch will send the frame to all the ports. In this way, the collision domains are
separated in their own ports and will not extend to other ports. The switch, as a
kind of transparent device, does not change the source and destination addresses
of the Ethernet frames, but forwards them to the proper LAN segmentations. The
switch usually uses the special ASIC chip to implement the bridge switching.
Although the switch has solved the problem of severe collision caused by using
hub, it still cannot separate the broadcast. In fact, all the hosts (perhaps including
many switches) interconnected by switches are in one broadcast domain. For the
broadcast packets with full "F" (0xffffff) as their destination MAC address, such as
ARP request packet, the switch will forward them to all the ports. In this case, the
broadcast storm will be caused and the performance of the entire network will be
deteriorated.
to interconnect the LANs. The switch establishes a MAC-PORT mapping table with
the source MAC addresses of frames received. For the received data frames, the
switch will look up their destination MAC address in the mapping table. If it can
find the destination MAC address, the switch will send the frame only to the port
corresponding to the address, or if it cannot find the destination MAC address, the
switch will send the frame to all the ports. In this way, the collision domains are
separated in their own ports and will not extend to other ports. The switch, as a
kind of transparent device, does not change the source and destination addresses
of the Ethernet frames, but forwards them to the proper LAN segmentations. The
switch usually uses the special ASIC chip to implement the bridge switching.
Although the switch has solved the problem of severe collision caused by using
hub, it still cannot separate the broadcast. In fact, all the hosts (perhaps including
many switches) interconnected by switches are in one broadcast domain. For the
broadcast packets with full "F" (0xffffff) as their destination MAC address, such as
ARP request packet, the switch will forward them to all the ports. In this case, the
broadcast storm will be caused and the performance of the entire network will be
deteriorated.
The technology of VLAN (Virtual Local Area Network) comes into being to solve
the problem that using switches to perform LAN interconnection cannot limit the
broadcast. In this way, One LAN is divided into several logical "LAN"s (VLANs),
with each VLAN as a broadcast domain. In each VLAN, the hosts can communicate
with each other just as they are in a LAN, but the VLANs cannot interact with one
another directly. Therefore, the broadcast packets are restricted in one VLAN, as
shown in the following figure:
the problem that using switches to perform LAN interconnection cannot limit the
broadcast. In this way, One LAN is divided into several logical "LAN"s (VLANs),
with each VLAN as a broadcast domain. In each VLAN, the hosts can communicate
with each other just as they are in a LAN, but the VLANs cannot interact with one
another directly. Therefore, the broadcast packets are restricted in one VLAN, as
shown in the following figure: