What's in your wiring closet?

A recent spate of Layer 3 and Layer 4 switch announcements would seem to suggest that the technology is moving from the enterprise backbones to desktop connections, with the promise of better application performance and reliability at the LAN edge.

While some users might long for the simple days of desktop hubs, there are benefits to pushing more switch intelligence closer to the wiring closet, some observers say. But some are skeptical, saying the technology amounts to costly wiring-closet overkill and unneeded complexity.

Cisco, Extreme Networks and Foundry Networks last month came out with new Layer 2 gear touted as "Layer 3 aware" or having "Layer 3 and 4 services." Vendors such as 3Com, Hewlett-Packard, Allied Telesyn and Nortel also offer such devices. Most switch vendors also have full Layer 3 gear and Layer 3 software upgrades targeted for wiring closets.

The switches in most vendors' Layer 2 to Layer 4 LAN edge portfolios break down as follows:

• Pure Layer 2: The long-standard Ethernet connection for nonrouted networks that use media access control address to move traffic.

• Layer 3 and Layer 4 "aware": Layer 2 switches with added software or silicon that lets the switch look into and make use of the IP address and TCP/User Datagram Protocol (UDP) information in packets. This allows features such as access rules based on IP addresses or the application of quality of service (QoS) based on IP address or TCP/UDP port type.

• Full Layer 3 and 4: Hardware-based routers with full routing and support for protocols such as Open Shortest Path First (OSPF) and routing information protocol. They move packets based on TCP/IP addresses. They also can classify traffic based on TCP/IP information for QoS and security purposes, and use routing to increase bandwidth on uplinks.

Some say full Layer 3 switching in the wiring closet can be valuable because of the QoS and security features. Plus a fully-routed network distribution layer can provide increased bandwidth and quicker failover of links in a wiring closet.

Layer 2 networks use the Spanning Tree Protocol (STP) for rerouting traffic around a downed link, but this requires an unused uplink connection to be present if a primary link goes down. Wiring closet boxes can be "dual-homed" to let two live Fast or Gigabit Ethernet links connect to different backbone or aggregation switches by using Layer 3 switching and OSPF. This allows up to 2G bit/sec of bandwidth to the switch and provides almost instantaneous failover if an uplink goes silent.

The Layer 3 Extreme BlackDiamond 6804 chassis switch is used in wiring closets at the Appleton School District in Wisconsin, which has 26 schools connected via Gigabit Ethernet over fiber.

"We're connecting Layer 3 right to the desktop," says Brent Braun, network infrastructure and security specialist for the school district. "We basically have routers in the wiring closet, but we're not using the [BlackDiamond] for routing as much as we are for Layer 4 switching."

Braun uses Layer 4-based rules on the switches to allocate bandwidth to certain applications, such as voice over IP and the school's administrative applications, over other traffic such as e-mail and Web surfing, he says.

Layer 2 QoS packet prioritization was not adequate for the Appleton deployment, Braun says. "You have a problem if you have a rush of junk suddenly being sent over your pipe [with Layer 2 prioritization]. Bandwidth utilization at Layer 3 and 4 allows for voice to get a certain percentage of the pipe, so no matter how much junk goes through there, voice will always get its required amount of bandwidth," he adds.

Layer 4 technology in LANs also has caught on with users. A recent survey of 500 Network World readers showed that 33% of enterprise users have bought Layer 4 switches while another 13% said they will buy the technology during the next two years.

Some vendors say their switches with Layer 3 and Layer 4 services are an alternative to putting routed ports out to users.

"We are actively discouraging customers from deploying Layer 3 routing to users," says Maciej Kranz, director of marketing for Cisco's desktop switching business. Using Layer 3 and Layer 4 packet inspection on Layer 2 desktop ports adds QoS and security features, and keeps the deployment simple, he says.

While there are benefits such as added security and quicker routing between virtual LANs with full Layer 3, Kranz says most deployments he's seen have Gigabit uplinks that are routed, and 10/100Mbit/sec end-user ports running at Layer 2.

One analyst sees Layer 3 as complete overkill for wiring closets.

"[For] the vast majority of configuration, full Layer 3 routing in the wiring closet is not necessary," even for uplinks running OSPF, says Lawrence Orans, senior analyst with Gartner.

"It becomes an administrative nightmare once you turn on Layer 3 devices," he says. "Essentially, you have more routers in the network and more routing tables, which increases problems and complexity when someone has to troubleshoot the network."

Layer 3 technology has come down in price, according to IDC, with the average Layer 3 port down about $130 from last year. But at around $430 per connection, Layer 3 still costs more than three times as much as a Layer 2 LAN port. Still, the research firm predicts that by 2006, one-quarter of all LAN switches shipped will be Layer 3, and Layer 3 switch port revenue will account for more than 60% of the total market.

It might not be this year or next year, but lower prices for switches and the development of bandwidth-hungry applications will cause more users to put Layer 3 ports in new parts of their networks, another observer says.

"Inevitably, everyone will have to be at Layer 3 at the desktop," says Martha Young, research director at Enterprise Management Associates. "This will be necessary to support collaborative applications such as voice and video over IP."

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