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New Member

Dual T1's to Internet

I'm looking at getting redundant/load balancing T1's to the Internet from two different providers. I am getting Primary DNS and ip addressing from provider A, but if either circuit fails I need our perimeter router to be able to advertise that it can be reached via provider A or B.

Is this doable/practical, or should I break down and get dual T1's from a single provide but originating from different CO's?

New Member

Re: Dual T1's to Internet

Doable yes.. practical.. depends on your needs. Is paying for two T1's practical for your operation? Could you use a more affordable lesser solution as a failover or are you really needing this much bandwidth from two points?

New Member

Re: Dual T1's to Internet

We have approval from headquarters for the dual T1, so I have to figure out the IOS setup to pull it off.

Besides that, what were you thinking of as the lower cost failover?


Re: Dual T1's to Internet

Very doable, but you need to evaluate your options carefully. You will discover that the better your ISP diversity (improving availability, if done right), the less effective and more difficult your load balancing.

My general rule of thumb is that for a reasonable level of effort, you can get perfect load balancing using multiple links to a single router at a single ISP, reasonable load balancing using diverse links to multiple POPs of a single ISP, and lucky to be within a two to one ratio using links to two independent ISPs.

Of course the other side of the coin is the size of the failure required to bring down your internet connection. But use care in your design so that the diversity you're paying for is maintained all the way to your computer room, if not to your users. It's amazing how the construction guys always pick the most critical links to cut :-)

The is a brief white paper outlining your ISP connectivity options on my web site, and several example configurations are explained in my book. Plus there are many examples here on CCO.

Good luck and have fun!

Vincent C Jones

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