Case Study: Stacking for simplicity

When some network architects deploy thousands of LAN ports for users, they use chassis switches at the LAN edge for easier management and fail-over. However, Duke University in North Carolina finds better network management and cost savings through stacking switches.

The university has a 15,000-node campus network with more than 30,000 switch ports. Most of these are fixed-configuration ports on Cisco Catalyst 3750-series stackable switches. Kevin Miller, senior manager of network services at Duke, says being able to stack his 3750-series switches has saved the school thousands of dollars in support and maintenance costs, and provides the same level of advanced management features as costlier, chassis-based Cisco switches.

"We're very happy with the 3570 stacking technology," Miller says. "We determined it was more cost-effective than a chassis solution."

The stacking technology Miller uses is called Cisco StackWise. This uses a daisy chain of proprietary interconnects to link as many as nine switches with a virtual backplane. The most recently-released 3750-E series supports 64Gbit/s, while the previous version supported 32Gbit/s. (3Com, Nortel, Extreme Networks, Foundry Networks and HP have competing switch-stacking technologies.)

Because the 3750s come with a limited lifetime warranty, which includes software support and ten-day hardware replacement, Miller forgoes the annual Cisco SMARTnet maintenance contract required for the chassis-based Catalyst switches.

"We had a big debate about our support strategy during our last SMARTnet go-around," Miller says. "We decided to keep a spare stock of 3750s for critical hour-one replacement." He says he and the network staff are comfortable enough troubleshooting the devices themselves that the high-level SMARTnet support was not worth the US$300 to $500 price per switch.

Although SMARTnet offers same-day equipment replacement -- within four hours -- "we would have spares anyway, because even a four-hour wait for new equipment is too long sometimes," Miller says.

The StackWise technology that links 3750 switches provides many of the same features as managing a chassis-based switch. Stacks of 3750s are seen on the network as one virtual device with a single IP address. Management software lets administrators create policies and make changes that affect the stack as a whole, instead of configuring individual boxes.

Duke uses dozens of 3750-switch stacks to support all aspects of the campus network, from wiring-closet connections to aggregation layer and backbone.

"It really does appear as one big switch" when multiple 3750s are liked via StackWise, Miller says. "That’s powerful, because it means all of our monitoring and management tools don’t have to poll as many devices." This greatly reduces the amount of SNMP, network probing and other management traffic that might otherwise congest the LAN.

"It just simplifies network management," Miller says.