Nevertheless, the term multilayer switch seems to be the best and most widely used description of this class of product that performs both Layer 3 routing and Layer 2 switching functions. Many new switching products are being introduced and their various naming schemes are confusing. These are described here, with some guidelines to help you recognize which is which. Layer 3 routing calculations are performed only on the first packet in a data flow, either by a router or by a separate route server. Following packets that are identified as belonging to the same flow are switched at Layer 2 along the same route.
Different vendors implement the cut-through scheme using a variety of proprietary technology.
As a result, cut-through routing products from different vendors can rarely interoperate to exchange routing information or continue forwarding the data at Layer 2. This variation of generic cut-through routing is based on ATM cells rather than frames, and products referred to as IP switches and tag switches generally fall into this category. However, ATM networking requires a significant initial investment as well as extra training to allow IS managers to support its higher complexity. Accordingly, this option makes sense only if an ATM structure in the network is dictated by other concerns. Learning Bridging - Layer 3 learning bridging differs from the other architectures in that it performs no routing whatsoever.