185
The switch supports communication within a common VLAN using store-and-forward
switching. However, if you have devices in separate VLANs that need to communicate,
and it is not practical to include these devices in a common VLAN, then the VLANs can
be connected via the Layer 3 routing provided by this switch.
Traditional routers use only physical port numbers in their routing tables, which provides
no support for VLANs. By contrast, this device supports Layer 3 routing by using both
logical and physical port numbers to support VLANs and Layer 3 switching
simultaneously.
By using the abstraction of a logical port number to represent a collection of physical
switch ports in the same VLAN, Layer 3 switching can occur from one VLAN to another
transparently, without changing the routing protocol and IP routing software, while Layer
2 switching is still used for intra-VLAN traffic.
The switch uses standard routing tables that are constructed via static configuration or
dynamic routing protocols such as RIP and OSPF. Each routing entry consists of a
network address (that is, an IP address with a subnet mask), and a virtual interface
number. Each virtual interface corresponds to a virtual LAN, identified by the VLAN ID.
Also note that multiple routing entries can be provided for the same virtual interface by
adding the required routing table entries for the same VLAN (chapter 2 “Subnet
Configuration” and chapter 3 “Subnet Configuration”). A typical VLAN configuration that
supports routing is shown below.