Riverstone Networks WICT1-12 - Manual (Page 67)

Riverstone Networks RS Switch Router User Guide Release 8.0 5-3
Bridging Configuration Guide VLAN Overview
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.
Multicast-based VLANs
Multicast-based VLANs are created dynamically for multicast groups. Typically, each multicast group corresponds to
a different VLAN. This ensures that multicast frames are received only by those ports that are connected to members
of the appropriate multicast group.
Policy-based VLANs
Policy-based VLANs are the most general definition of VLANs. Each incoming (untagged) frame is looked up in a
policy database, which determines the VLAN to which the frame belongs. For example, you could set up a policy
which creates a special VLAN for all E-mail traffic between the management officers of a company, so that this traffic
will not be seen anywhere else.
5.3.1 RS VLAN Support
The RS supports:
• Port-based VLANs
• Protocol-based VLANs
• Subnet-based VLANs
When using the RS as an L2 bridge/switch, use the port-based and protocol-based VLAN types. When using the RS
as a combined switch and router, use the subnet-based VLANs in addition to port-based and protocol-based VLANs.
It is not necessary to remember the types of VLANs in order to configure the RS, as seen in the section on configuring
the RS.
VLANs and the RS
VLANs are an integral part of the RS family of switching routers. The RS switching routers can function as layer-2
(L2) switches as well as fully-functional layer-3 (L3) routers. Hence they can be viewed as a switch and a router in
one box. To provide maximum performance and functionality, the L2 and L3 aspects of the RS switching routers are
tightly coupled.
The RS can be used purely as an L2 switch. Frames arriving at any port are bridged and not routed. In this case, setting
up VLANs and associating ports with VLANs is all that is required. You can set up the RS switching router to use
port-based VLANs, protocol-based VLANs, or a mixture of the two types.
The RS can also be used purely as a router, i.e., each physical port of the RS is a separate routing interface. Packets
received at any interface are routed and not bridged. In this case, no VLAN configuration is required. Note that
VLANs are still created implicitly by the RS as a result of creating L3 interfaces for IP and/or IPX. However, these
implicit VLANs do not need to be created or configured manually. The implicit VLANs created by the RS are
subnet-based VLANs.