Tip of the Trade: Managed Switches
June 25, 2007
We all know and love our plain old ordinary "dumb" (read: unmanaged) network switches, like the Netgear GS108 ProSafe Gigabit Ethernet switch, the TRENDnet TEG-S224 Copper Gigabit Switch or the SMC SMCGS8 Gigabit Unmanaged Switch. For well under $100 you can have gigabit Ethernet. This is mind-boggling for anyone who grew up in the era of hubs (remember collision domains?) and kilobit network speeds.
As with all things high-tech, devices improve and drop in price at the same time. Managed switches used to be a big-ticket line item that required considerable justification. Now they're down in the sensible price ranges, which is good for frugal network admins who want it all for cheap. Managed switches don't make sense on a small LAN, but when you're riding herd on 25 or more users, they can be real time-savers. Managed switches vary considerably in price and feature set. Some key things to look for are:
SNMP Support: A switch that supports SNMP means you can monitor it with OpenNMS, MRTG or any SNMP-based network monitor.
Bandwidth Rate Limiting: It's easier to do this on a switch than using something like tc (Traffic Control), which is powerful but difficult. And it's platform-independent, which is always a good thing.
Virtual Local Area Network (VLAN): Once you get the hand of VLANs you'll never go back to the bad old days. VLANs let you create logical subnets, rather than having to re-arrange switches and cables whenever you want to make changes.
Port Mirroring: Because switches don't spew everyone's packets to everyone, you can't sniff the traffic for a whole subnet like you can with a hub. Managed switches should include port mirroring to allow you to do this.
Port Trunking: A cool feature that lets you combine ports for more bandwidth and for fault-tolerance. Build your own mega-backbone on the cheap!
Duplexing and Priorities: Some managed switches let you turn duplexing on and off, and assign some ports higher priorities.
You might also look for switches that let you collect all sorts of traffic data and statistics. This is very helpful in finding bottlenecks and tracking down trouble spots. How much will this cost? Good choices can be found in the $250 to $500 dollar range. Here are a few examples. Note that they are not recommendations.