Network Layer Switching For The Corporate Intranet By Joel Conover   There's no doubt that the corporate intranet is here to stay. Higher utilization of internal networks demands a healthy combination of routing and switching to keep your network running in tip-top condition. To get you moving on your intranet, we tested three products at our University of Wisconsin labs that provide scalable switching solutions with the enhanced ability to route OSI Layer 3 traffic. To view the Report card. More than just a router slapped into an existing switch, the Layer 3 switch employs high-powered ASICs and advanced switching techniques to move Layer 3 packets smoothly through a Layer 2 device. We tested products fr om Cabletron Systems, Case Technology and 3Com Corp. Each solution offers a distinct approach to routing Layer 3 traffic across the switching domain. The Layer 3 switch is an extremely efficient way to address your intranet routing issues, combining high-speed routing with minimal trade-offs. VLAN Support One unifying feature of the switches we tested is virtual LAN (VLAN) capabilities. Until now, adding VLAN features to your network meant sacrificing connectivity among segments. However, with fast, integrated routing built into the switch, VLANs have become a practical tool for segmenting networks. Each of the three switches we tested is targeted for a specific market. Some switches behave like active routers, making them look like a typical router to the external network; others use the passive router implementation, switching traffic directly to its destination without performing the route-advertising functions of a traditional router. Your needs will dictate the features to look for. Cabletron Systems Ethernet MMAC-Plus SmartSwitch If you're shopping for an enterpri se installation, you can't afford to pass up Cabletron Systems' SmartSwitch line. We tested the largest model in this line, the Cabletron Ethernet MMAC-Plus. It should be noted that the entire SmartSwitch line offers the same functionality as the MMAC-Plus. When it came to performance, we couldn't bring the SmartSwitch down. We established 10 full-duplex conversations over Ethernet, both locally and between two switches, and the Cabletron switch never blinked an eye, giving us 297,600 packets per second (pps)--the equivalent of 20 line-speed Ethernet streams routed simultaneously. Packet Tracking The heart of the Cabletron solution relies on the switch's ability to keep track of every packet that comes into a port and its destination. This means the switch looks at every packet and associates Layer 3 information to its Layer 2 Media Access Control (MAC) address. This lets the switch "cut-through route" any packet for which it knows the end-to-end connection. When a SmartSwitch receives a packet destined for an unknown MAC address, it behaves like a normal switch and floods that packet out the ports on the local VLAN. For a packet with a known MAC address, the packet is forwarded to its destination, even if that MAC address is on a different IP subnet or switch. The MMAC-Plus chassis has 14 slots, and each blade in the chassis behaves like an independent switch. That means if you have five Ethernet boards and an FDDI interface, you effectively have six switches in your chassis. The entire group of switches is connected via MMAC-Plus' 2.5-Gbps passive backplane. The advantage to this design is resiliency--if any switch blade fails, the rest of the network is unaffected. The drawback is the design is not very intuitive and eats up IP addresses (you need one for every blade in the switc h).

Updated January 10, 1997