Food for ANCR bloodhounds.
New directions in Layer 3 switching
Vendors use packet-by-packet routing, software solutions to attain higher throughput, better management on the network backbone
By Kristina B. Sullivan, PC Week Labs
02.18.98
Wire speed--that's what the latest Layer 3 switches are striving for. By performing packet-by-packet routing techniques in ASICs, these devices achieve speeds of 4 million, 7 million, even 30 million packets per second.
"We're putting resources in the switch to handle packet-by-packet look-ups on the fly," said Basil Alwan, director of product management for Bay Networks Inc.'s switching products division, in Santa Clara, Calif. To achieve that, Bay's Accelar 1200, released last month, performs simultaneous packet look-ups on 24 engines.
Among the latest to join this class of switch routers is the SmartSwitch router line from Cabletron Systems Inc., which obtained the switch through its acquisition last month of Yago Systems Inc.
Cabletron expects to ship an eight-slot model in the second quarter of this year that will support up to 14 Gigabit Ethernet and 56 Fast Ethernet ports, followed by a 16-slot version in the second half that can provide up to 30 Gigabit Ethernet and 120 Fast Ethernet ports. Each model will offer IP and IPX protocol support and speeds of 15 million to 30 million packets per second.
The SmartSwitch router represents an about-face for Cabletron, which uses cut-through Layer 3 switching technology in its current line of SecureFast switches. With packet-by-packet Layer 3 switching, each packet is examined and forwarded to its destination. Cut-through Layer 3 switching examines the first packets to determine the destination and sends the rest through. But Cabletron sees a place for both Layer 3 switching techniques.
"What this boils down to is offering our customers a wider array of choices when they build their networks," said Trent Waterhouse, a senior architect with Cabletron, in Rochester, N.H. "In the past, our only option was cut-through. The SmartSwitch router allows Cabletron to offer standards-based, packet-by-packet routing." While SecureFast switches can still be used effectively in contained subnets, SmartSwitch routers are targeted at the network backbone.
One advantage of cut-through Layer 3 switching is lower price. Cabletron's hardware-based, cut-through SecureFast switches are about $250 per Fast Ethernet port, compared to $499 for a comparable SmartSwitch port.
Drawbacks to cut-through Layer 3 switching include networkwide software changes, the chance of errors and the use of proprietary techniques. "Cut-through is not going to survive, and packet-by-packet will dominate," said Alwan. "It's simpler and does not force the one-vendor decision that all cut-through schemes do."
Packet-by-packet switches read everything into a buffer and make sure there are no defects before forwarding a transmission, while cut-through switches send packets out before the whole sequence is in. With cut-through, defective packets could already be on outbound ports by the time you realize they're defective, said Henry Hartman, brand manager for IBM's ATM switch products in Research Triangle Park, N.C.
"With packet-by-packet, we are able to apply network-layer services such as security, quality of service and policy enforcement," said Nathan Walker, product line manager for gigabit multilayer switching at Cisco Systems Inc., in San Jose, Calif.
For ATM networks, however, the industry takes a different approach, with cut-through as the clear winner.
"When ATM is in the center, the best way to achieve high-speed Layer 3 is through MPOA [Multiprotocol Over ATM], said Alwan. Bay's Centillion 100 ATM switch uses cut-through MPOA technology. Similarly, IBM's 8265 ATM switch is a cut-through model, while its ASIC-based 8274 Nways LAN RouteSwitch Ethernet switch uses packet-by-packet technology.
Software-based Layer 3 switching devices are also contenders in this market, and some of the products are from the same companies providing ASIC solutions.
For example, 3Com Corp. offers a software-based cut-through Layer 3 switching product called Fast IP. "Say you just went out and bought half-a-million dollars' worth of routers. You're not likely to replace them all with Layer 3 switches," said Clint Ramsay, director and business unit manager for 3Com's LAN Systems division, in Boxboro, Mass. Fast IP allows network administrators to increase the performance of an existing, routed network, he said.
Although software-based solutions are slower than ASIC models, they're less expensive. For example, RND Networks Inc.'s software-based Apollo-Pro provides packet-by-packet IP/IPX routing for more than 600 ports for $9,200. In comparison, the CoreBuilder 3500 configured with 24 Fast Ethernet ports is $27,395.
"Although the Apollo-Pro is fast, it has limitations because it is in software, not an ASIC box, and is limited to 50,000 packets per second," said Mike Long, vice president of marketing for RND Networks, in Mahwah, N.J. Users can add RND's PowerIP cut-through software to increase performance, he said.
Features to look for in Layer 3 switches
Both IP and IPX support
WAN interfaces such as T-1 and T-3
Redundant power supplies
Redundant CPU modules
RMON support
Web-based management
Fast Ethernet, Gigabit Ethernet support
ATM, FDDI support (or plans)
Layer 3 switching products also differentiate themselves with such features as multiprotocol support, WAN interfaces, multiple network types and long-distance Gigabit Ethernet. Cabletron's SmartSwitch router will support both IP and IPX; 3Com's CoreBuilder 3500 will add IPX to its IP protocol support this month (and later AppleTalk); Cisco's Route Switch Module includes IP, IPX, AppleTalk, DECnet, VINES, XNS and SNA routing.
Growing support for WAN interfaces is apparent in Cisco's Route Switch Module for the Catalyst 5000, which provides T-1 and T-3 connections. Cabletron plans ATM and Synchronous Optical Network interfaces in the second half of this year.
Among those supporting multiple network types are 3Com's Fast Ethernet CoreBuilder 3500, which will gain Gigabit Ethernet support this quarter, FDDI in the second quarter and ATM in the third quarter. In May, OneBox Networks Inc., in Westlake Village, Calif., will ship two new versions of its ASIC-based ON-516A 16-port Fast Ethernet switch that includes Gigabit Ethernet uplinks and ATM.
NBase Communications Inc. announced long-distance Gigabit Ethernet at ComNet last month. "When the [Gigabit Ethernet] standard is voted on in the next month or two, the distance will be 2 kilometers, but we are using laser and fiber-optic technology to take the NBase GigaFrame switch to 100 kilometers," said Jeff Graham, director of marketing for NBase, in Chatsworth, Calif.
Similarly, Bay's Accelar 1200 currently supports Gigabit Ethernet at 3 kilometers, but Bay has already tested it with transceivers that provide up to 10 kilometers.
Vendors agree that application-level prioritization is the next frontier for Layer 3 switches. "Users will be able to take a particular application with a well-known port number, such as CU-SeeMe or PointCast or HTML traffic, and prioritize or de-prioritize it across the network," said Alwan.
3Com plans to make such capabilities more automated in the future to allow policies on one Layer 3 switch to be applied to multiple switches, said Ramsay.
"Classifying traffic and enforcing attributes such as security will provide quality of service," he said. "The ability to classify traffic at wire speed, to prioritize multiple queues and to allocate bandwidth through the system--those are differentiators that will become more important over time."
Acclaim Communications Inc. is readying what it calls a Layer 3-Plus upgrade to its EtherWAN 2000 Series Ethernet switches to ship in March. "You can now figure out things like what is the application that is being run," said Vish Akella, president and CEO of Acclaim, in San Jose, Calif. One use of this technique could be to specify that certain users are allowed to check stock quotes between 9 a.m. and 5 p.m., Akella said.
The Acclaim switch's management software will prompt the network manager to set priority levels for E-mail and other applications as they are used. Voice and video applications, for example, could be assigned a certain bandwidth level to guarantee quality of service.
Other applications that could take advantage of such advanced features include direct access to voice lines. "A person browsing the Web could have a question and automatically click over and talk to someone," said Akella. "We are trying to mimic the telephone industry. First, there was a party line, then a single digital line, now there is conferencing and broadcast dialing. The same pattern is happening in data networks to give users all of the features of broadcasting, conferencing and security."
Contributing Editor Kristina B. Sullivan can be reached at kristina_sullivan@zd.com. |
