Scorecard and NetResults How and why we ranked the hubs the way we did. VLANs review Network World, 2/17/97. Mier is president, Smithers is manager of lab test services and Scavo is lab test coordinator at Mier Communications, Inc., a Princeton Junction, N.J.-based network consultancy and product test center. They can be reached at (609) 275-7311 or via e-mail to ed@ mier.com, rob@ mier.com or tom@ mier.com.

By Edwin E. Mier, Robert J. Smithers Jr. and Thomsa R. Scavo
Network World, 6/9/97

Yesterday's hubs are toys compared to today's souped-up hardware. Specialized, high-end, multislot switching hubs have grown in features and capacity, sporting capabilities you could only dream of five years ago. This crop of hubs gives you lots of flexibility and centralized control while interconnecting all manner of switched links.

For the review portion of this Buyer's Guide, we looked at systems that provide at least 1G bit/sec of switching capacity, support any-to-any switching between at least two high-speed switching technologies - 100Base-T, FDDI or ATM - and can handle at least eight 100M bit/sec switched LAN segments.

Cabletron Systems, Inc.'s MMAC-Plus chassis with SmartSwitch modules proved to be an exceptionally versatile system with some impressive and useful advanced features, such as those for switch-to-switch link redundancy and load sharing. And based on the moderate-to-heavy test traffic loads we delivered, we found it's an exceptional performer, too. It captured our Blue Ribbon for this test.

Cisco Systems, Inc.'s Catalyst 5000 is oriented to Ethernet and Fast Ethernet switching. We found some limitations with the switching module it offers for FDDI, and ATM wasn't provided by the vendor for this test. But for managing it all, the other two hubs couldn't match the functionality and intuitiveness of the CiscoView management application.

Digital Equipment Corp.'s MultiSwitch 900, which we tested with a variety of the vendor's new VNswitch modules, handles moderate loads of LAN traffic well and provides easy, out-of-the box switching between Ethernet, Fast Ethernet, FDDI and ATM. However, we found that the system misfired under high-traffic loads. All in all, Digital made a good showing, but the competition was better.

We invited Bay Networks, Inc. to show off its latest System 5000 switching hub. Bay declined. So did 3Com Corp., which claims to offer a couple of different systems that would seem to fit the bill. Some other vendors couldn't satisfy all the requirements or indicated their latest switching hub wares weren't quite ready for testing. FORE Systems, Inc. and Xylan Corp. both declined. IBM was also invited but never contacted us.

Cabletron: MMAC-Plus is a winner

The system has a number of internal backplane buses that collectively yield a lot of bandwidth and a high degree of configuration flexibility. For example, there's a 200M bit/sec, dual-FDDI internal bus that handles repeater-hub, token-ring multistation access unit (MAU) and concentrator-type modules. Then there's a 72-bit internal parallel bus - 64 bits of which are used for data and eight for access and control overhead - to which the switching modules interconnect. There's even a separate 10M bit/sec bus that can be used exclusively to carry all management traffic for sites with dedicated management nets. Indeed, it's completely up to the user whether management traffic goes in-band - that is, along with user data - or via this out-of-band channel, which assures reliable management access in the event of network problems or hardware outages.

The 64-bit switching bus, which operates at a 40-MHz clock speed and uses an efficient time-division multiplexing (TDM) access scheme, yields an impressive 2.5G bit/sec of switching bandwidth.

Cabletron offers some 70 different modules for the MMAC-Plus, which run the gamut from token-ring MAU cards to ATM 155M bit/sec links. Density is also impressive. You really can pack the system with switched network links - more than 500 switched 10Base-T links can be configured in the 14-slot MMAC-Plus (via 36-port modules) or 168 switched 10/100 links.

In our maximum load test, we delivered four concurrent 100M bit/sec traffic streams. The packets of each stream were switched to four destination ports on a round-robin basis in rapid succession: a packet stream delivered at wire speed on a Fast Ethernet interface was broken down and switched by the MMAC-Plus to an FDDI, an ATM and two Fast Ethernet output ports.

The MMAC-Plus' any-to-any switching and throughput performance was the best of the three systems we tested. We were impressed: 400M bit/sec of traffic load being switched at wire speed between Fast Ethernet FDDI and ATM links and not a single packet was lost or misdirected.

All data is sent over the MMAC's switching bus in the packet structure native to token ring and FDDI. So while packets to or from Ethernet or Fast Ethernet have to be converted, data to or from FDDI or token rings does not.

We were impressed by the wealth of options for interconnecting switches. Some of these rely on the vendor's proprietary SecureFast architecture, which embodies Cabletron's virtual LAN capabilities.

One of the SecureFast options we tested was the ability to run multiple, parallel 100M bit/sec Fast Ethernet links between two switches, in which all the links share the load and provide hot-standby redundancy for each other. Such capabilities are not inherently supported by standard Fast Ethernet, which many consider a drawback to 100Base-T technology.

We configured three parallel Fast Ethernet links between two switches and delivered a 60M bit/sec traffic load over each one. Then we physically disconnected one of the links to see what would happen. It took just slightly longer than one second, but the complete 60M bit/sec load of the disabled link was automatically shifted to the remaining two links. Total traffic lost during the switchover: about 100,000 packets. Still, given this volume of load and the reliability of the switchover, this unique capability of Cabletron's works well.

Another welcome feature we tested, also part of the SecureFast architecture, is the switch's ability to resolve IP addresses between nodes on different VLANs and selectively allow them to exchange traffic as a router would. With this feature, broadcast traffic still does not pass between VLANs, but point-to-point IP conversations, such as Web-based intranet sessions or File Transfer Protocol file transfers, can occur between nodes on different VLANs - and without requiring a separate router.

Otherwise, Cabletron's VLANs are based mainly on individual nodes' media access control addresses. This is a level of sophistication above Cisco's and Digital's VLANs, both of which are based solely on lower level port groupings.

What are Cabletron's weaknesses? Well, we weren't too crazy about the vendor's suite of management offerings. For basic chassis and module management, we had Cabletron's Unix-based Spectrum. We found this software to be complex and far from intuitive to use. While the full-blown Spectrum on Unix is more substantial than the Windows management applications from Digital and Cisco we used in this test, Spectrum is appropriate for managing large networks with a lot of Cabletron equipment.

Cisco's equivalent application, CiscoView, was by far the best of the three tested for this aspect of management.

We also examined Cabletron's new VLAN Manager application Version 1.5, which runs as an add-on with Spectrum. Fortunately, it has its own intuitive graphical user interface. Given the current VLAN management wares from Cisco and Digital, we consider Cabletron's the best VLAN management application.

For traffic monitoring, Cabletron included its new Remote Monitoring (RMON)-based application, which we found rough around the edges. Unlike Spectrum, though, we were able to obtain accurate and understandable, real-time traffic reports via this separate RMON application. Still, the RMON package leaves a lot to be desired as far as usability. Digital's RMON Manager Version 3.3 was the best of the three traffic monitoring applications we examined.

Catalyst 5000: Ethernet leader

The Catalyst 5000 configuration we tested goes for $42,000, including the switching engine module, two 10/l00Base-T switching modules and an FDDI switching module. If an ATM module were included - making the configuration comparable with those of Cabletron and Digital - it would have bumped the list price up by $10,000, to a total of $52,000.

The Catalyst 5000's top slot requires one of Cisco's switching engine modules, leaving only four slots for other modules. This highlights the fact that switching is more centralized with the Catalyst, while it is more distributed to individual switch modules in the Cabletron and Digital architectures. The switching engine module in the Catalyst 5000 can also be viewed as a single point of failure.

Switching in the Catalyst 5000's top slot uses a 48-bit-wide bus that operates at 25 MHz, yielding a "gross'' system switching bandwidth of 1.2G bit/sec. But unlike the TDM-based access mechanism of Cabletron's MMAC-Plus, Cisco uses an arbitration access scheme, which tends to involve more overhead. Still, according to Cisco, about 1G bit/sec of "net'' system switching bandwidth is available for user data across the backplane of the Catalyst 5000.

While Cisco now ships an ATM uplink module for the Catalyst 5000 switch, it didn't include one with the model we tested. Cisco's ATM module cannot be used to directly interconnect Catalyst switches; all ATM connections must go through an external ATM switch. Cabletron and Digital support direct connection of their respective switches via ATM.

Cisco does offer a broad assortment of modules for the Catalyst 5000, including various Ethernet and l00Base-T hub modules (as opposed to per-port switching modules). However, certain technologies, such as token ring, are not supported.

The Catalyst 5000 is clearly oriented toward Ethernet and Fast Ethernet switching. All traffic is moved across the system's switching bus in Ethernet packet format. This means there's no reformatting or conversion required for packets coming from or going to Ethernet or Fast Ethernet ports, but translation is needed for data switched to or from FDDI or ATM.

Our performance tests showed that the Catalyst 5000 could handle most, but not all, of the heaviest traffic loads we delivered. With four 100M bit/sec packet streams, delivered via l00Base-T ports and switched on a round-robin basis to FDDI and other l00Base-T ports, we noted packet loss between 8% and 10%.

Most of this loss, however, occurred with traffic being switched between 100Base-T and FDDI. Cisco acknowledges that its current FDDI switching module for the Catalyst 5000 can handle no more than about 100,000 packet/sec. Each of the high-volume test traffic streams we delivered via Fast Ethernet ports applied a traffic load of nearly 150,000 packet/sec, so we were overloading the FDDI switch module by about 50,000 packet/sec.

We observed that throughput for the Catalyst 5000 was best for traffic switched between Ethernet and Fast Ethernet ports, as expected, because no conversion of packet format is needed in that case. Indeed, when we switched a couple of 100M bit/sec traffic streams between just Fast Ethernet ports without any FDDI in the picture, there was no packet loss.

As noted, we regard Cisco's CiscoView application as the best of the three vendors' packages we examined for hub chassis and modules management. Cisco's new VLAN Director software Version 1.3 is a bit complex and takes some getting used to. For configuring VLANs across Catalyst 5000s, we preferred to use the more basic VLAN components of CiscoView rather than the VLAN Director application.

For traffic monitoring, Cisco's suite, collectively called CiscoWorks for Switched Internetworks, now also includes Traffic Director. This is a version of Frontier Software Development, Inc.'s RMON application, which Cisco adopted. This software, like VLAN Director, is tedious to set up and use. Also, it does not appear to be well-integrated with the SNMP or RMON components in the Catalyst 5000. Rather, it seems oriented more toward use with separate, stand-alone RMON probes.

Digital: Mixed-port ace

VNswitch modules are offered in switched Ethernet-only versions and in combinations of switched Ethernet and your choice of Fast Ethernet, FDDI or ATM ports. The modules plug in to and interconnect over the 400M bit/sec VNbus of the MultiSwitch 900. Each module contains its own switching intelligence, thus distributing intelligence evenly across modules, in additiom to its own SNMP agent for management.

An array of other hub-type modules is offered for the same MultiSwitch 900 chassis, so this is a fairly flexible and configurable system. These other modules include token-ring MAU, Ethernet repeater and FDDI concentrator modules.

However, Digital doesn't offer a high-density 10/l00Base-T MultiSwitch 900. Instead, two switched 100Base-T ports come on a switch module along with 12 switched Ethernet ports, so a fully configured MultiSwitch 900 can support a maximum of 16 100Base-T ports. Our test unit included three Ethernet/Fast Ethernet, one Ethernet/FDDI and one Ethernet/ATM module. Its list price was $51,000.

While the MultiSwitch technically supports a total gross switching bandwidth of 1.2G bit/sec, this is distributed over three 400M bit/sec channels. And all switched traffic passing between ATM, FDDI, Ethernet and Fast Ethernet goes over just one channel - the VNbus. Digital says it plans for future switch modules to also use the other backplane channels.

The vendor describes the VNbus as a serial, cell-based bus, although variable-length chunks of data are transported, not fixed-length, ATM-type cells. Access is arbitrated, as with the Cisco architecture. According to Digital, it is the sending module's job to perform conversion of the data, if necessary; for example, on packets going be-tween a switched Ethernet and a switched FDDI module. A tagging protocol is used internally to designate what technology - and, if applicable, what VLAN - the data is associated with.

The ATM module's capabilities are fairly rich. Switches can be directly linked via ATM using a variety of tunneling techniques, or data can be shipped via an ATM uplink to an external ATM switch using standard ATM LAN Emulation 1.0.

By far the most significant advantage of the MultiSwitch 900/VNswitch system we found is its plug-and-play ability. We simply plugged in a random mix of Ethernet, Fast Ethernet, ATM and FDDI modules and were immediately able to send switched traffic between any ports. All the configuration and translation is done automatically.

However, while traffic of small to medium loads is switched neatly and automatically between different types of LANs, the system exhibited some peculiar behavior under heavy loads.

With the heaviest load test - four streams of 100M bit/sec each delivered on Fast Ethernet ports and switched on a round-robin basis to FDDI, ATM and other Fast Ethernet ports - there was usually some loss of data packets switched between Fast Ethernet and FDDI and also between Fast Ethernet ports. It appeared, however, that an excess of data was switched onto the ATM link. In other words, not all packets were forwarded correctly at high-traffic loads. Some outbound ports received too few packets, others received too many. Our conclusion: The system cannot reliably handle this load.

Digital's management software suite, called clearVISN, also includes separate applications for chassis/module management, VLAN management and traffic monitoring. The VLAN Manager Version 1.0 we tested was quirky and generally nonintuitive, even though all user actions are accomplished via point-and-click operations.

We found Digital's MultiChassis Manager Version 6.1 to be an effective tool for chassis and module management, but for this purpose, not quite as sophisticated or easy to use as CiscoView.

Digital's traffic monitoring application, RMON Manager Version 3.3, was the best of the management tools for this purpose, compared with the equivalent traffic monitoring applications from Cisco and Cabletron. Digital's RMON application is intuitive and integrates well with the traffic monitoring components integral within each VNswitch module.