A mirage at Layer 4

Networking vendors turn up the fast-pipe hype, but real speed gains may be elusive

By Stephen Lawton

Network managers in most businesses are just beginning to invest in Layer 2 and Layer 3 switching, but some vendors are already promoting Layer 4 technology, sparking a debate over its relevance.

All parties agree that one benefit--wire-speed routing and switching is indisputable; however, skepticism persists on whether it results from mining data found in Layer 4 or whether it's actually more attributable to improvements in ASIC technology.

Still others claim that touting Layer 4 capabilities is marketing run amok.

The debate lies in the definition of what actually occurs at Layer 4, defined in the OSI (Open Systems Interconnection) Model as the transport layer. Companies such as Torrent Network Technologies Corp., Yago Systems Inc., and Alteon Networks Inc. strongly promote their products' use of information from the User Datagram Protocol (UDP) and TCP ports to control data flows as the reason they can qualify as Layer 4 devices.

However, competitors such as Cisco Systems Inc. assert that all of the functionality promised in today's Layer 4 switches is already available in current router products--except for the wire-speed performance.

Routing takes place at Layer 3, the network layer, where the source and destination IP addresses are found; standard switching takes place at Layer 2, the data-link layer, where the source and destination MAC addresses are paired.

A layer's a layer
All of the data in an IP packet, regardless of layer, can be accessed by a processor-based router or switch. The difference between traditional routing and the new devices, according to Basil Alwan, director of product management at Bay Networks Inc. in Santa Clara, Calif., is speed. A processor-based system often takes too long to glean information from the header to be useful, he said. As capabilities such as security are added, the devices take a performance hit. The new generation of routing-switch products use ASICs to make routing decisions, letting the units operate at wire speed. Because the various network services are implemented in hardware, there is no performance hit to turn on a feature.

All routers and switches have three primary functions: filtering packets, forwarding packets, and providing differentiated network services. Given this basic definition, the differences between the emerging network devices and traditional routers, said Alwan, are merely speed and the capability of using more features with wire-speed performance.

Landover, Md.-based Torrent's marketing vice president, Gordon Saussy, agrees that labeling a device as Layer 4 can be misleading. "I'm not a big enthusiast of the [Layer 4] term," said Saussy, noting that simply "looking at the header is not terribly important." What is significant, he noted, is that ASIC-based routing provides scaled IP routing in which data flows can be identified and processed at wire speed.

Piyush Patel, president and CEO of Yago Systems in Sunnyvale, Calif., another of the startups that calls its products Layer 4 devices, agrees--to a point. Patel acknowledged that all the functions offered by Layer 4 vendors are available in traditional devices, but that's where the similarities end, he said. Like Torrent's IP9000 Gigabit Router, Yago's MRS 8000 supports full routing and switching at wire speed of 1.488 million packets per second (pps); the Cisco 7500 router tops out at a range of roughly 1 million pps, he said. The new devices also are much less expensive than the 7500-class routers.

Alteon Networks in San Jose, Calif., claims that its AceSwitch 110 goes beyond the capabilities of today's routing devices by being capable of connecting clients to servers running specific applications based on a load-sharing approach. But San Jose-based Cisco's Jayshree Ullal, vice president of the company's enterprise group, said that capability already exists today using the Hot Standby Routing Protocol, which lets a backup router take over if the primary router fails. In fact, Ullal said, today's Layer 4 products fall short of traditional routers in that they support only IP and IPX and not the other routing protocols.

If the Layer 4 debate isn't confusing enough, next month a new company will announce a device that it describes as a "layerless" router. According to Neo Networks Inc. in Minnetonka, Minn., its product will handle multiple-gigabit data flows in real time. Instead of using UDP and TCP ports, the unit looks at the data itself to determine the application and makes decisions based on preset policies regarding who has access to which data. Neo's product uses seven ASICs and RISC processors to manage networks and to process data flows based on information at Layers 2 through 7 in real time, rather than just IP addresses or TCP or UDP ports.

But much of this debate is lost on IS managers. Mark Wiesenberg, director of computer services at QUALCOMM Inc. in San Diego, said that, while some of his networking specialists might debate the apparent merits of reading various header information, he doesn't care about layers. His concerns are more basic: Does it work?

Although vendors heavily promote their products' respective benefits, he said, he resists getting too involved in marketing. "The bottom line," he said, "is when I plug it in, does it do what it's supposed to do."

That is similar to the attitude of Steve Davis, a senior manager in the IS department at Buena Vista Television, a Disney Inc. company in Burbank, Calif. Davis said his concerns are based on how well a product functions, rather than how a company specifies it.

Even industry analysts can't agree on the benefits of labeling products Layer 4. Last month, Decisys, a Sterling, Va.-based consultancy, issued a white paper titled "Layer 4 Switching," in which analysts Jonathan Bransky and David Passmore discussed in detail the performance, security, and packet-forward benefits found in so-called Layer 4 devices.

However, Craig Johnson, director of Network Infrastructure Services at Current Analysis Inc., also in Sterling, said "I don't know what [Layer 4] means." While acknowledging that this class of routing switch can look deeper into the packet header, Johnson said it is an "industry imperative to define a standard for looking at Web usage." That class of device will offer a variety of high-performance features, he said, but vendors are "spinning those solutions to call [the new products] Layer 4."

John Morency, an analyst at The Registry Inc., a consultancy in Newton, Mass., compares the layer debate to the beer advertising slogan: "Tastes Great, Less Filling." Companies such as Cisco Systems and IBM, which focus on multiprotocol routing, packet accounting, and firewalls, are in the "Less Filling" category, he said. High-speed switching vendors such as Bay Networks, Alteon Networks, and the "gigabit router startups" focusing more on data flows and high-speed links are in the "Tastes Great" category. Both groups provide similar functionality but use marketing as the differentiating factor, he said.

Bay's Alwan explained it this way: "The market is just understanding this [class of routing and switching]. A lot of [network managers] haven't had the light bulb go on yet."


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