Tip

Chassis or stackable?

This tip is in response to a question I hear a lot, and recently saw in the

.Yc8Iat8ZWRV.1@.ee83d5e/726!viewtype=convdate&skip=&expand=">Network Design forums.

The basic query was 'should I use stackable switches or chassis-based switches?' As was pointed out in the question, stacking several 24 or 48 port switches together is usually much cheaper than putting the same number of 24 or 48 port blades in a chassis, but the chassis offer better management.

What's interesting about this, is that almost all switch manufacturers make switches in both configurations. Perhaps they recognize that both have appropriate niches in the networking world, or perhaps they recognize that the question has turned into a religious issue, with a polarized administrator base that reminds me of a certain beer commercial. I can just hear the pro-chassis camp screaming "Tastes great!" and the pro-stackable camp responding "Less filling!"

But how does one decide which is more appropriate for their network? I believe the answer lies in recognizing the advantages of the chassis, then deciding whether any of those features are useful in your situation, and if so, are they worth the extra cost?

Chassis-based solutions can generally do everything their stackable cousins can do, plus they have the following advantages:

  • Easy redundancy: external redundant power supply solutions are available for stackables, but more common for chassis. Redundant supervisor blades are also common in chassis, but I don't usually recommend them. I hear of line cards failing almost weekly, but in 15 yrs of networking, I can't remember ever hearing of a supervisor failure.
  • Flexibility: it is easier to move ports around to different VLANs, span or mirror ports, and it's easier to upgrade or replace components in a modular chassis.
  • Performance: stackable solutions are generally limited to 1 or 2 gigabits in and out of each switch. Theoretically, twenty-four 100Mb Ethernet ports would be capable of 2400Mb/s, and it's twice as bad at 4800Mb/s for a 48 port blade. Is this a problem? Rarely, if ever. However, chassis solutions use proprietary backplanes that can be much, much faster than the standards-based Ethernet protocol. (Some stacks (e.g. Nortel's 450T) do use a proprietary backplane.)
  • Features: chassis switches often support more queues and thresholds per port, so QoS is much more granular. As new features come out, upgrading your supervisor module is a whole lot less expensive than upgrading all your ports.
  • When you have to do emergency or routine code upgrades and patches, it's a lot easier to do it once, than once for each of 8 switches in a stack.
  • Fewer electrical outlets are required and cabling solutions are more aesthetically appealing. Fewer IP addresses are required for management. Rack space is also saved. This isn't too important in most wiring closets, but in a datacenter, where floorspace is often more expensive than the equipment, it can be a major factor.
  • Many other components are being integrated into chassis. For instance, in Cisco's 6500 chassis, you can put VoIP Gateway blades, the super-fast Firewall Services module, intrusion detection and other blades.

So as you can see, the answer usually revolves around cost, as always, but cost can be a little more complex than it appears. Consider the "Total Cost of Ownership", including things like the potential labor savings from reduced management, and the extended useful life gained by upgrading components, instead of just the purchase price and the chassis becomes much easier to justify. Nevertheless, if you don't need any of those features, you can save a lot of money and get the same performance from the stackables.


Tom Lancaster, CCIE# 8829 CNX# 1105, is a consultant with 15 years experience in the networking industry, and co-author of several books on networking, most recently, CCSPTM: Secure PIX and Secure VPN Study Guide published by Sybex.


This was first published in June 2004

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