Routing between VLANs using virtual routing interfaces (Layer 3 Switches only)

RUCKUS calls the ability to route between VLANs with virtual routing interfaces Integrated Switch Routing (ISR) . There are some important concepts to understand before designing an ISR backbone.

Virtual router interfaces can be defined on port-based, IP protocol, IP subnet VLANs.

To create any type of VLAN on a RUCKUS Layer 3 Switch, Layer 2 forwarding must be enabled. When Layer 2 forwarding is enabled, the Layer 3 Switch becomes a Switch on all ports for all non-routable protocols.

If the router interfaces for IP is configured on physical ports, then routing occurs independent of the Spanning Tree Protocol (STP). However, if the router interfaces are defined for any type VLAN, they are virtual routing interfaces and are subject to the rules of STP.

If your backbone consists of virtual routing interfaces all within the same STP domain, it is a bridged backbone, not a routed one. This means that the set of backbone interfaces that are blocked by STP will be blocked for routed protocols as well. The routed protocols will be able to cross these paths only when the STP state of the link is FORWARDING. This problem is easily avoided by proper network design.

When designing an ISR network, pay attention to your use of virtual routing interfaces and the spanning-tree domain. If Layer 2 switching of your routed protocols (IP) is not required across the backbone, then the use of virtual routing interfaces can be limited to edge switch ports within each router. Full backbone routing can be achieved by configuring routing on each physical interface that connects to the backbone. Routing is independent of STP when configured on a physical interface.

If your ISR design requires that you switch IP at Layer 2 while simultaneously routing the same protocols over a single backbone, then create multiple port-based VLANs and use VLAN tagging on the backbone links to separate your Layer 2 switched and Layer 3 routed networks.

There is a separate STP domain for each port-based VLAN. Routing occurs independently across port-based VLANs or STP domains. You can define each end of each backbone link as a separate tagged port-based VLAN. Routing will occur independently across the port-based VLANs. Because each port-based VLAN STP domain is a single point-to-point backbone connection, you are guaranteed to never have an STP loop. STP will never block the virtual router interfaces within the tagged port-based VLAN, and you will have a fully routed backbone.