An OcNOS Hybrid Switch Router offers Layer 3 forwarding found in routers with the high-speed performance associated with traditional Layer 2 switches. The following are some advantages of Hybrid Switch Routers:

Layer 2 and Layer 3 switches are similar at a high-level, both look at the packet headers, and steer the packets toward their destination port. Therefore, after being passed through a switch or router, the packet is closer to its destination.

Layer 2 switches are typically used to provide connectivity within high bandwidth local area networks (LANs). A Layer 2 switch makes forwarding decisions based on the MAC or the Layer 2 header. It extracts the Layer 2 header from the packet, finds a matching destination address in the forwarding table, and transmits the packet out to the port associated with the specific destination address in the forwarding table. The forwarding table is populated through a self-learning process, whereby each arriving packet is used to update the entries in the table. Typically, the Layer 2 switch implements the switching function in the hardware, as that requires stripping of the packet only in two layers (the physical and data link layer) to get to the useful part of the packet header. This allows switches to steer packets at wire-speed rates without slowing down arriving streams of packets to process them.

Layer 3 (L3) routers are typically used to provide connectivity between different LANs. A Layer 3 router discards MAC headers, and indexes further into the packet–making decisions based on the IP or Layer 3 header. It extracts the Layer‑3 header from the packet, finds a matching destination address in a routing table, identifies a new MAC address for the packet from an ARP cache, wraps the IP packet in a new MAC header, and then transmits the packet out to the port associated with that destination address in the routing table.

The routing table is populated through statically configured command line interface entries or through routing protocol messages from neighboring routers. A Layer 3 router must strip through 3 layers (physical, data link, and network) which is more complicated than a Layer 2 switch. Layer 3 routers historically implement the routing function in software. This often results in limited packet-forwarding rates. However, improvements in VLSI circuit technology have allowed Layer 3 routing functions to be implemented rapidly in hardware, enabling wire-speed performance similar to the performance of Layer 2 switches. As a result, along with the complexity of next-generation Layer 3 routers, the throughput of these routers has also been increasing.

An architecture is required that is flexible enough to accommodate the demands of different customers, and accommodate the changing demands of a single customer whose requirements may change over time. Typical Layer 2 switches and Layer 3 routers fail to provide this flexibility.

An optimal configuration can be an integrated solution, a Layer 3 router with Layer 2 bridge groups around it. The OcNOS Hybrid Switch Router implementation allows easy configuration of different combinations of routers and switches. OcNOS can be configured as an absolute Layer 3 router, absolute Layer 2 switch (Figure 29-146) or a hybrid Layer 2/Layer 3 switch router, (Figure 29-147) that can easily change modes with the use of a single command.

Thus it can work as a router, a switch, or as a hybrid switch.

With only Layer 2 protocols configured, the OcNOS Hybrid Switch Router can become an absolute Layer 2 switch.

With Layer 2 and Layer 3 protocols configured, the OcNOS Hybrid Switch Router can become a Switch and/or a Router.

With only Layer 3 protocols enabled, the OcNOS Hybrid Switch Router can become an absolute router.

On switch ports, VLANs can be created for different broadcast domains.

For routing between VLANs, the OcNOS routing protocols or static routing via NSM can be utilized.

For routing between VLANs and other routing ports, OcNOS routing protocols or static routing via NSM can be utilized.