Layer 3 switches take the fast route

| SPECIAL TO GCNIn the best of all possible networks, large volumes of data flow from high-end workstations and data centers, and e-mail messages with complex multimedia attachments flit about effortlessly, all without bringing transmissions to a crawl.That day is coming, as networking technologies improve, but it won't be tomorrow. In the meantime, the best most organizations can afford is a mix of 10-Mbps Ethernet and 100-Mbps Fast Ethernet service to the desktop PC, with one or two Gigabit Ethernet backbone links.align="left" width="210">Ethernet has dug in as the world's most popular network topology for good reasons. Using small servers and inexpensive hubs, many organizations can get by with shared 10-Mbps or 100-Mbps bandwidth to the desktop for noncritical applications such as departmental e-mail. For more critical applications, 10/100-Mbps Ethernet switches can provide dedicated bandwidth to users at wire speed. Meanwhile, 1-Gpbs Gigabit Ethernet switches can be used effectively to connect high-speed servers or link to network backbones.This guide features 10/100 Layer 3 Fast Ethernet switches designed mainly to provide dedicated high-speed bandwidth and routing capabilities to multiple workgroups at the edges of large networks.This category of hardware barely existed a year ago. Limited numbers of Layer 3 Gigabit Ethernet switches with a few 10/100Base-T ports were available. But there were very few Layer 3 10/100 switches for workgroups and small departments.Things are changing. In a search of more than 70 switch manufacturer Web sites, I found 18 companies that make Layer 3 switches targeted to the dedicated 10/100 Fast Ethernet market. Most also make Layer 3 Gigabit Ethernet products.I selected 10/100 switches that come in eight-, 12-, 16- and 24-port configurations for workgroup service. Many of the products listed are modular or stackable, and can provide switching for up to 96 ports. Most also offer one or two optional or built-in slots for Gigabit Ethernet backbone links or 100Base-FX fiber links.The accompanying chart lists only a sampling of available switches from each manufacturer. Check the companies' Web sites to find other switches in the Layer 3 category; one of them might best meet your requirements.The real benefits in Layer 3 switches come in the routing of data. Layer 2 switches can deliver dedicated data to any station on the network at wire speeds because they don't have to handle individual data packets and route them to their destinations'that job, by definition, belongs to network routers.But because most of a LAN's legacy routers are software-based, they can't keep up with Layer 2 switch speeds. Traffic bottlenecks often occur wherever they are installed.Layer 3 switches bypass this problem by combining the raw throughput speeds of Layer 2 switches with advanced routing technology. They are built around hardware-based, application-specific integrated circuits and specialized switching fabrics, which enable them to handle packet forwarding much faster than can software-based routers. Most Layer 3 switches employ software protocols running in the background over built-in RISC processors to help them perform routing calculations at similar, lightning speeds.Some advanced routing protocols, more commonly known by their acronyms, include Routing Information Protocol (RIP and RIP2), Open Shortest Path First (OSPF), Dynamic Host Configuration Protocol (DHCP) and Bootstrap Protocol (BootP), and multicast protocols such as Distance Vector Multicast Routing Protocol (DVMRP) and Internet Group Management Protocol (IGMP).Layer 3 switches not only overcome slow packet routing, they also alleviate common problems encountered with flat Layer 2 networks, such as broadcast storms and address limitations. As a result, managers can configure and manage large network segments more easily without having to create as many subnets'using traditional routers'as they did in the past.More of the management capabilities of layers 4 through 7 currently are being built into the newest Layer 3 switches.Layer 4 is the transport layer of the Open Systems Interconnect model and is used with the other top layers of the OSI model to help prioritize traffic types and allow users to specify applications that should receive high priority. For example, a switch with Layer 4 capability could set a lower priority for departmental e-mail than for mission-critical data from a high-end system.Beside their terrific performance ratings, the best thing about Layer 3 switches is their price relative to other network gear. Per-port Layer 3 switch prices range from a low of about $150 per 10/100 port to $500 or more depending on the features'with one or two Gigabit Ethernet slots often included.XXXSPLITXXX-