Closet and Edge Switches

The Essentials

What must your edge/closet switch do? The answer will steer you to the right switch. Are you setting up a studio for a videographer? Building a plain-vanilla branch office? Adding a testing lab? Hiring call-center flunkies relying on VoIP (voice over IP)? Hanging wireless access points hungry for PoE (power over Ethernet)?

Consider whether 24 ports will be enough for the life of the switch--you might hit that ceiling in a year or two. If you're working with an existing infrastructure or you must adhere to a corporate standard, your product choices are likely to be further constrained.

If you're looking to VoIP, most vendors offer support for Layer 2 (802.1p) traffic prioritization and Layer 3 QoS (quality of service). Look for strong support for VLANs (virtual LANs), which is a must for installing VoIP in your shop--security is strongest when the PBX and phones are on their own VLAN. Even lower-priced switches support at least 255 VLANs, which should be enough for most shops. If you're adding a switch to a complex infrastructure and your choice isn't limited by other factors, select a switch that supports more than 4,000 VLANs and 64,000 MAC (Media Access Control) addresses.

Switch Fabric bandwidth--the switching fabric that makes up the backplane of these switches--may play a part in your decision. A 24-port gigabit switch with an 8.4-Gbps fabric may meet the needs of a real estate office, but be brought to its knees by a newsroom feeding off multiple video sources. If you move a lot of large files (CAD drawings, images, full-screen video), up the specs on the switching fabric to avoid unhappy users.PoE (or IEEE 802.3af) provides DC juice through Cat 5 cable to devices, such as wireless APs. This allows more flexibility in placement and simplifies wireless rollouts. PoE is also used for VoIP phones. You might not need PoE now, but with the relatively small upcharge over comparable non-PoE gear, it's not a bad option compared with picking up dedicated PoE injectors later. Check the maximum wattage provided and verify that it's more than your worst-case planned draw. Typically, a phone requires 6 to 8 watts; APs need 3 to 11 watts.

If you don't want to be paged at 2 a.m. because of toasted power supplies, consider products with secondary power-supply options--internal or external. Many of the less-expensive switches in this 1U form factor don't offer power redundancy, but you can find gear to suit your needs without stepping up to a chassis-based switch. And always consider putting a UPS in your closet to keep your switch humming during brownouts.

All major switch vendors offer some management tools, from telnet command lines to Web applets. To zero in on specific management needs, ask: Do you care about management other than through a serial connection? Will you need manageability by way of remote access? If so, is SSH (secure shell) a concern? Will you integrate this switch with SNMP tools, such as those provided by Hewlett-Packard OpenView or IBM Tivoli? Management capabilities vary by switch--more money buys you more sophistication. Higher-priced switches are more likely to comply with SNMP standards, meaning that error conditions will be reported reliably, rollover counters will work accurately and tables will age properly.

Confer with your business manager, customers and staff to determine the maximum number of ports needed, as well as how many PCs, IP phones, APs, NAS boxes, servers, printers and other Ethernet-enabled devices will be hanging off a port. Then round up. One 48-port switch generally will cost less than two 24-port switches, take up less rack space and generate less heat. Most of the products in this niche are 1U boxes, and you could run into trouble if your closet space is constrained.

If you plan to connect two switches, or if you must connect your new closet switch to the existing backbone, you'll have to rely on uplink ports. Your options range from built-in serial and Gigabit Ethernet uplinks to plug-in modules offering up to 10 Gbps over glass. Be sure your uplink solution will be compatible with your existing gear. To minimize risk, many shops follow a one-vendor rule. If you want to employ switches from multiple vendors, look for standard protocols (such as 802.11q VLAN tagging) rather than proprietary schemes. The more uplink bandwidth you require, the more you should plan on spending. There's no need to buy a 2-Gbps GBIC (Gigabit interface converter) if you're never going to upgrade your 100-Mbps backbone.Network design is essential; if all file sharing and client-server activity will take place between computers hanging off the new switch, you needn't fuss over the uplink. But if all 20 staffers in your art department will be pounding the heck out of the NAS that's back at your core switch, look for a bigger pipe to your backbone.

Calling the Maytag Man

Warranties on closet and edge switches range from one year to lifetime, depending on vendor and product. Factor in the value of the service contract as you shop, and compare apples to apples in your evaluations. If the switches you're considering have a useful life expectancy of five years, for instance, check out the price on comprehensive, long-term coverage. And if the network is critical to your business, weigh the price of a spare switch against the cost of being out of commission until a replacement arrives should something go wrong.

Joe Hernick, PMP, MS, is director of IT at the Loomis Chaffee School. Dean Ellerton, MS, is the CIO at Suffield Academy. Write to them at [email protected].

Edge/Closet Switch Checklist1) Will the new switch work with your current hardware? Does it support standard protocols?

2) How many ports do you need? Will you need an uplink port? Will copper suffice?

3) Does the switch support PoE? Do you have redundant power supplies?

4) How many VLANs and/or MAC addresses do you need?

5) Does the switch support wirespeed ACLs, which provide better performance and security?6) Does the switch support SNMP and SSH for remote management?

7) Do you need RIP?

For details and prices on specific systems, use our Interactive Buyer's Guide charts.

STP (Spanning Tree Protocol): A Layer 2 protocol, such as IEEE 802.1d, Rapid Spanning Tree Protocol 802.1w, that resides on switches. STP's purpose is to avoid a loop situation when you have redundant network paths by blocking one or more redundant ports in your topology. STP monitors the network for environmental changes, and will reconfigure your ports automatically to avoid nastiness. 802.1w promises faster resolution over 8021.d.

RIP (Routing Information Protocol): RIP version 1 is a Layer 3 distance-vector routing protocol that counts router hops. Version 2 incorporates VLSMs (Variable Length Subnet Masks) and CIDR (Classless Interdomain Routing), with support for route authentication and multicasting of route updates.OSPF (Open Shortest Path First): Uses a link-state algorithm to build and calculate the shortest path to all known destinations for a packet.