Load balancing routers

Self build / N/A
February 1, 2009 at 06:12:48
Specs: xp pro, AMD 64x2
At my computer club we have two ADSL lines, each connected to a four-port router. Each router supports four PCs.
Each ADSL line delivers 2Mb/s approx.
I have been considering buying a load balancing router such as the Draytek Vigor 2820 and connecting all eight PCs to it, but am not clear exactly how it works.
I believe that if one ADSL line goes down, all PCs will still get an internet connection.
However, does it also mean that the bandwidth is aggregated such that a pc could have access to 2 x 2= 4Mb/s?

Thanks in anticipation

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February 1, 2009 at 06:22:54
It also means that if the Dual WAN router fails, you would have no internet connection instead of 1. Are both DSL connections from the same provider?

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February 1, 2009 at 06:40:34
Yes they are from the same provider at the moment.

Do you know whether the two bandwidths would be aggregated?


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February 1, 2009 at 08:37:19
That would be one of the specs you would look for when you do your dual wan port router research..

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February 1, 2009 at 08:46:46
That's very helpful!

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February 1, 2009 at 13:37:36
Make sure your router supports link load balancing - as this is not 'regular' load balancing (it's reverse-load balancing, or bandwidth aggregation).

I've made a setup like this before w/ 3 DSL lines, aggregated on a freebsd router I put together.

I dunno about that specific load balancer, an old Alteon could do this no problem. The one I built used the built in IPFW firewall w/ sourcing routing to handle the differnet links.

As you ask '2 x 2= 4Mb/s?' generally not for one host - you generally set this up w/ one host going out one line, so 1 computer would still only get 2mb. Trying to distribute bandwidth more evenly than this it becomes difficult to maintain state -- I could never get per/connection distribution to work right in my freebsd setup.

But, remember this will not be one circut - so you could never pull 4mb's on ONE download - as one tcp session can only use one link at a time, but you could pull 4mb from two different sites, etc.

This also depends on your distribution method - i.e., how do the connections get distributed for the two lines? (Random, round robin) ?? The best method is of course using a 'bandwidth metric' - where the next line to use is determined by which one hast he least amount of traffic going through it -- you don't normally find this option on cheap load balancers.

I dunno about that LB you mention, but do know that a cheap-load balancer will probably not distribute the traffic correctly& you need to know what you're looking for. Personally, I would build it myself.

I've seen someone do this w/ a windows box too - though I have no idea how...

a cheapo box w/ 2 nic's running freebsd/linux can do this too, and it'll help you understand more what you're doing.

There's also some company out there that builds routers specifically designed to aggregate DSL lines like this -- I can't remember the name...I'll post it if I do.

Anyway, good luck w/ this

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February 1, 2009 at 19:31:30
I never recommend dual homed computers, especially in place of a good router.

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