Cabletron Systems SmartSwitch Router, Руководство пользователя

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SmartSwitch Router User Reference Manual 57
Chapter 3: Bridging Configuration Guide
• Multicast based
• Policy based
Detailed information about these types of VLANs is beyond the scope of this manual.
Each type of VLAN is briefly explained in the following subsections.
Port-based VLANs
Ports of L2 devices (switches, bridges) are assigned to VLANs. Any traffic received by a
port is classified as belonging to the VLAN to which the port belongs. For example, if
ports 1, 2, and 3 belong to the VLAN named “Marketing”, then a broadcast frame received
by port 1 is transmitted on ports 2 and 3. It is not transmitted on any other port.
MAC-address-based VLANs
In this type of VLAN, each switch (or a central VLAN information server) keeps track of
all MAC addresses in a network and maps them to VLANs based on information
configured by the network administrator. When a frame is received at a port, its
destination MAC address is looked up in the VLAN database. The VLAN database
returns the name of the VLAN to which this frame belongs.
This type of VLAN is powerful in the sense that network devices such as printers and
workstations can be moved anywhere in the network without the need for network
reconfiguration. However, the administration is intensive because all MAC addresses on
the network need to be known and configured.
Protocol-based VLANs
Protocol-based VLANs divide the physical network into logical VLANs based on
protocol. When a frame is received at a port, its VLAN is determined by the protocol of
the packet. For example, there could be separate VLANs for IP, IPX and Appletalk. An IP
broadcast frame will only be sent to all ports in the IP VLAN.
Subnet-based VLANs
Subnet-based VLANs are a subset of protocol based VLANs and determine the VLAN of a
frame based on the subnet to which the frame belongs. To do this, the switch must look
into the network layer header of the incoming frame. This type of VLAN behaves similar
to a router by segregating different subnets into different broadcast domains.