Network World — Six years ago, we tested dual-WAN routers as a way to pump more bandwidth into small businesses that couldn't afford a T-1 and were stuck with relatively slow DSL and cable connections.

Today, speed is less of an issue. For example, our suburban test lab has an 18Mbps connection with AT&T's U-verse service and 15Mbps (with burst downloads as high as 30Mbps) with Time Warner (TWX) Cable's Road Runner Turbo.

The critical need today is maintaining connectivity. The ability for dual-WAN routers to combine throughput from two sources, continue if one drops, then reconnect when the link comes back is a key selling point.

Of course, cost is important, too. A T-1 delivers better uptime than any connection from a phone or cable company, and a synchronous connection in and out, but at hundreds of dollars a month. Two 15M to 20Mbps small business broadband connections combined provide far more downstream throughput and 100% network redundancy, all for a total of $80 to $120 per month.

We tested six dual-WAN routers: Check Point 1000N, D-Link DFL-210, Netgear FVS336G, SonicWall TZ200, TRENDnet BRV324 and Xincom DPG603. All units share a fairly long list of standard features, including VPN support, DMZ support, some level of QoS, and firewalls of varying strength and granularity. Several of the more expensive units offer intrusion detection and prevention.

We found that the ability to separate traffic between two active WAN links is much improved compared with our last test. All units allow you to weight one WAN connection more heavily than the other in order to push traffic in that direction. Most offer ways to segment users or protocols to a specific WAN link. All support firewalls capable of passing the full throughput of almost all inexpensive broadband links that will be tied together by these dual-WAN routers.

Dual-WAN routers don't really double the throughput to any one computer, but they deliver their true worth when several computers are pulling lots of traffic. No longer will the video download fanatic suck up all available bandwidth.

In our redundancy testing, each router continued after one WAN link was dropped, and recovered when the link came back up. The occasional five minute "pause" that randomly afflicts residential broadband service in our area disappeared, as the second WAN took up the slack invisibly.

Our VoIP phone had connection troubles with some routers when we configured them to split traffic based on bytes or packets. Setting the load balancing metric to IP addresses eliminated those issues.

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