Dual WAN router testing: Good and bad about load balancing

* Initial tests of a dual WAN router

In the last newsletter, we discussed our mostly-successful results from the initial testing of a router designed to use two broadband Internet service interfaces - such as using both cable modem and DSL service. With the low prices for these services, this seems like a logical answer to getting reliable high-speed service at a very low price. Today, we want to dig a bit deeper into some of the details, especially when using the routers in a load-balancing mode in which both services are simultaneously in use.

As has been mentioned in other sources, it's important to be able to assign particular traffic types to always be limited to one of the two interfaces. For instance, if you're sending e-mail using one of the service providers, you probably need to restrict outgoing e-mail traffic to that link. Making this example concrete, if you're using the e-mail service from the cable provider, odds are pretty good that messages coming from the DSL provider will be rejected. Since we use our own e-mail server, this was not an issue. However, the router has the option to limit certain traffic types to one of the interfaces. (Of course, the problem is that if the link for e-mail fails, you're still out of luck.)

The load balancing seemed to work quite well when going to normal Web sites. In fact, when accessing a site that determines your originating IP address, we could see both links were in use.

Then we found expected and unexpected glitches. For instance, load balancing provides no performance improvement for large file transfers. Once you're started with a single large FTP transfer, you get the performance of whichever link is in use. This is not the equivalent of Multilink PPP (ML-PPP). (Of course, the good news is you also don't have the negative performance impact of ML-PPP overhead.)

The biggest negative impact was that two applications in particular - WS-FTP and AOL Instance Messenger - performed extremely poorly when being load-balanced to the point that they were essentially unusable. We're in constant contact with the equipment supplier on trying to diagnose and resolve these issues but, for that reason, we're withholding a glowing review of the products until we get a bit further along in the review process.

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