The switch needs to perform both switching and routing. Switching is done in OSI layer 2, and is therefore needed between the controller connected as a homerun, and the controllers connected as a ring. Switching is simple and fast. The switch can identify where to send packets within a VLAN. The only additional configuration that is required is to assign the switch's ports to VLANs.
Routing is done in OSI layer 3, and is therefore needed between the controllers and the network engine when the network engine resides in a VLAN different than the controllers it supervises, and between the network engine and ADS. Routing connects different subnets and usually needs more configuration than switching. For a Metasys network, important routes are defined in the switch configuration. For example, the configuration includes explicit routing statements that tell the switch how to send packets between the network engine and the controllers. Every device needs a default route. A default route tells the device where to send a packet if it does not have any other information about the destination of the packet. The controllers and network engine have the address of the switch for their default route. If configured correctly, the switch will know where to send the packet next.
Switches have addresses and default routes like any other device. They have one MAC address for every physical port and virtual port. The basic IP address is the Switch management Virtual Interface (SVI). It may also manage the virtual interface for one or more VLANs. These virtual interfaces are used to construct the routing rules.