Switching grows up

By Susan Breidenbach
Network World, 5/4/98

The throngs invading Las Vegas this week for NetWorld+Interop 98 should have no trouble finding vendors hawking Layer 3 switches; in fact, getting away from them may be the problem. ATM had its turn, as did 10M and 100M Ethernet. Now it's routing switches that command the spotlight.

With this development, we've in a sense come full circle - from routing to bridging to switching and back to routing again, given that Layer 3 switching is basically routing repackaged. It seems appropriate, then, to call a timeout and assess this switching phenomenon - to examine how far switching has brought us, where we stand today, where the technology is poised to go and how we're going to get there. There's a lot to cover, so we've divided our report into several documents (or you can grab the entire report in a single file).

Today's networks are a far cry from what experts envisioned in 1990, when neat and tidy visions of end-to-end ATM connections and voice/data convergence were dancing in their heads. Ethernet switching was just a stopgap that would extend the life of aging technologies such as TCP/IP long enough for the new order to establish itself.

But the visionaries underestimated the inertia of the installed base and failed to learn the lessons of Open Systems Interconnection (OSI). Paradigm shifts bubble up from the bottom like natural ground springs; they aren't imposed from the top. As ATM slowly worked its way through standards committees, the Ethernet cadre rose to the challenge and in-creased network speed by two orders of magnitude in just seven years. Users started deploying ATM on the backbone, but the availability of a cheap, simple, high-speed Ethernet alternative effectively kept them from extending it to the desktop. And Ethernet will continue to dominate the desktop unless ATM prices come down and demand for ATM-enabled services goes up.

But Ethernet couldn't provide an end-to-end solution, either. While switches enabled the creation of larger Ethernet networks, they couldn't scale across the backbone because of management and spanning tree problems. It was a standoff until Layer 3 switching entered the picture.

"The advent of the Layer 3 switch is what made frame networks at the core possible," says Basil Alwan, vice president of product management at Bay Networks, Inc., in Mountain View, Calif. "You get one of the main benefits of ATM - you can switch or route equally fast. That has important implications for how you can build networks."

What's in a name?

Switching is one of the euphemisms that abounds in the politically correct 1990s as people use words to evade reality. Layer 2 switches are really multiport bridges, but routing was in, and the "B" word was out when the EtherSwitch was christened in 1990 (see story, this page). Similarly, the "R" word had become synonymous with slow, complex and expensive by the mid-1990s when the first Layer 3 switches - really hardware-based routers - appeared.

When bridging was invented in 1983, it outperformed and displaced the single-protocol routers then being used. But bridges propagated broadcast storms, so they were replaced by multiprotocol routers or put into silicon and called Layer 2 switches. Now routers are out of vogue, so they are being implemented in hardware and referred to as Layer 3 switches.

"Routing is not bad, it just needs to be a lot faster and cheaper," says Drusie Demopoulos, vice president of marketing for Foundry Networks, Inc., in Sunnyvale, Calif. Although Layer 3 switches generally support only IP, Layer 3 routing switches are an order of magnitude faster than the traditional software-based multiprotocol routers that put Cisco Systems, Inc. on the map. And while a routed 100M bit/sec Ethernet port is priced at about $750, a port on a traditional router can run $5,000 to $7,000.

The price/performance gains from replacing traditional routers with Layer 3 switches are thus much greater than those obtained by moving from hubs to Layer 2 switches. Industry observers think the price difference between a switched and routed port will drop to zero within two years. Extreme Networks, Inc., of Cupertino, Calif., has already announced pricing of $100 per port for switched and $150 for routed 100M bit/sec Ethernet.

Currently, vendors are each using their own custom Application Specific Integrated Circuits to manufacture Layer 3 switches. "The next trend is putting Layer 3 switching into standard silicon," says Diane Myers, a senior analyst at In-Stat, a consultancy in Scottsdale, Ariz. "We should see some announcements from the semiconductor companies within 12 months." This commoditization will help to reduce the cost of building Layer 3 switches (NW, March 2, page 39).

Meanwhile, Layer 3 switches can reduce the cost of network ownership by making it a lot easier for administrators to do moves, adds and changes. They don't need to know what physical port users are at.

Consequently, "[virtual LANs] are much easier to implement in Layer 3 switches," says Ori Bendori, chief technology officer for LANNET, a subsidiary of Madge Networks NV, based in Tel Aviv. "They are almost transparent."

When creating and managing VLANs at Layer 2, administrators have to track the physical ports and media access control addresses of individual users. At Layer 3, VLANs can be implemented by assigning IP subnets to them.

The main report:
To Part 2: Prospects for ATM and Wrong Assumptions
Winners & Losers and The next Cisco? | Over the horizon and Eliminating Layer 2?

Short takes:
Layer 4 switching: What it is and isn't
Where we've come from
Where we're going
Ten switching tips

The entire report in a single file