The many uses of the word "switching"

"Switching" is a term that is used in today's industry for any high-speed data forwarding technology - from ATM to bridging to routing to telephone circuits. When employing a LAN switch, make sure you're aware of not only what type of switching your switch is doing, but what other forms of switching are possible. Is it Layer 2 (bridging) or Layer 3 (routing)? Or something else?

Layer 2 switches forward packets only by MAC address and ignore all higher layer aspects of a packet. Layer 3 switches forward packets based on Layer 3 protocols, such as an IP subnetwork or IPX network address. (Note that some LAN switches do both Layer 2 and 3 switching.) Even more sophisticated switches that offer Layer 4 switching are becoming commonplace. Some vendors are planning switching at higher layers. We'll have to wait to determine just how useful upper layer switching will become.

Switching at the various layers of the protocol stack should be an architectural issue. For example, workgroups would use Layer 2 and points of aggregation such as backbones use Layer 3 switching. However, the massive increase in performance for Layer 2 and 3 switching, as well as an increase in the number of services a LAN switch can offer (for instance, priority and security), has muddied the water.

In the next issue, we'll discuss another face of switching that you should be aware of: Layer 3 switching. While it may seem that we already discussed this, that is exactly my point: Some vendors call the hybrid Layer 2/Layer 3 forwarding used to improve performance "Layer 3 switching" when it's actually Layer 2 routing-assist, which is used to reduce load on a router.

The Tolly Group, a strategic consulting and independent testing organization, offers a full range of services designed to furnish the vendor and the end-user communities with authoritative and unbiased information. The Tolly Group is a leader in assessing leading edge technologies and provides such services as: network design, product evaluations, industry studies, and market research. For more information, visit The Tolly Group's World Wide Web site, send e-mail to info@tolly.com, call 800-933-1699 or 732-528-3300, or fax 732-528-1888.

Switching grows up
Where switching has come from and where it's heading. Network World, 5/4/98.

Cheap switches will change the LANscape
As companies battle for market share, prices per port are falling. Network World, 2/9/98.

Switch vendors keep layering on the hype
NetWorld+Interop 97 saw a host of switch vendors labelling new routing products as Layer 4 switching. Network World, 11/3/97.

Switching routers answer the call for more bandwidth, performance
Network World, 6/30/97.

Switching at Every Layer: An Insider's Guide to Deciphering the Marketing Hype
This white paper from Torrent describes Layers 2 through 4.

Routing and Layer 3 Switching: Understanding the Critical DifferencesThis Torrent white paper focuses on the difference between Layers 2 and 3.

Multi-layer Routing
This page compares various proposals for the integration of layer 2 and layer 3.

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