LAN switches gear up for Web explosion

Communications News, Dec, 2000 by Morris Edwards

Adding functionality layer by layer.

LAN switches have come a long way since their introduction to relieve congestion in local area networks (LANs). Because of their ability to increase the performance of overloaded networks cost-effectively, LAN switches are rapidly becoming the preferred means for connecting hubs. routers. servers and even desktops.

At the same time, LAN switches are taking on more advanced capabilities to help IT managers who have begun deploying multiservice networks that optimize bandwidth use. prioritize traffic and guarantee application performance. In addition. the explosion in Web access and e-commerce has placed further demands on LAN switches, primarily to reduce user wait times, gain better control over content and provide seamless load-balancing functionality to the Web server network.

LAN switch vendors are addressing these more advanced needs by extending their products' functionality higher into the seven-layer open system interconnection (OSI) communications model.

Most of the original switches operated at the data link layer, or Level 2 of the OSI model. This meant using the source and destination media access control (MAC) addresses to determine if a packet should be forwarded, and to which port, based on an address table lookup. By dividing the network into segments and allowing the segments to operate without interference from traffic local to the other segments, the switches were able to dramatically increase the performance of heavily trafficked LANs. Today's more intelligent switches act on information beyond the Level 2 MAC addresses.

Layer 3 switches, for example, use information from the network layer, or Level 3 of the OSI model, to route packets at wire speed, raising performance to the millions-of-packets-per-second range, compared with thousands of packets per second with software routers. At the core of these devices is a switching matrix that provides fully switched connectivity down to the port level. Custom ASICs (application-specific integrated circuits) enable the wire-speed switching on a packet-by-packet basis.

Software routers have traditionally had the advantages over LAN switches of better WAN (wide area network) connection and multiprotocol support. To compete. LAN switch vendors are introducing high-speed WAN interfaces. ranging from OC-3 to OC-12 and beyond, for both asynchronous transfer mode (ATM) and packet-over-SONET (synchronous optical network) deployments. In addition, some vendors are adding support, through software, for protocols besides Internet protocol (IP). With these new features. LAN switches can compete effectively with software-based routers for both enterprise and service provider networks.

To distinguish between different types of applications, such as file transfers, Web browsing and real-time applications, LAN switches need to use packet header information beyond the network layer. Layer 4 switches, for example, might examine the TCP Port ID in the IPheader. Layer 4 filtering and forwarding allows managers to make more sophisticated decisions in such areas as traffic prioritization, bandwidth allocation, access control and load balancing. The switches are intended for IT managers who have to focus on maintaining service levels for selected, more critical users and applications because the traffic in their campus backbones is increasing at an unpredictable rate.

Switches that operate with information in Layers 5 through 7 of the OSI model provide even more sophisticated functionality. These intelligent-content switches typically provide the Layer 3 and 4 features, and add functionality by reading into the HTTP (port 80) request header. URL or "cookie." the bit of data that identifies users.

TOMORROW'S BACKBONE

Looking ahead over the next few years. IDC predicts that Layer 3 hardware switches will become the prevalent choice for LAN backbones. Gigabit Ethernet will be adopted in campus environments and for server consolidation, with the initial implementations in switch-to-switch implementations, just as with 100-Mbps Ethernet. LAN switches with tens of 100-Mbps connections matched to a few Gigabit Ethernet uplinks will become commonplace.

IT managers will look for scalable solutions that do not sacrifice latency or throughput as management features are activated. Security will also be a growing concern, resulting in the integration of such features as firewall and network address translation support directly into switch architectures.

IDC expects that organizations seeking to upgrade their campus infrastructures will inevitably deploy switches in a strategic role. Networks comprising high-density switches in the wiring closet/edge that cascade into Gigabit Ethernet Layer 3 or multiprotocol switches at the core are already routine. Some organizations have even begun to migrate their wiring closets to Layer 3. In the near term, however, IDC contends that Layer 2 switches with some advanced features, such as traffic filtering, are a simpler and more cost-effective approach for the edge.