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Getting the most out of an extra T-1 connection

Jul 14, 20032 mins
Internet Service ProvidersNetworking

As a cost saving move, we are changing ISPs.  In doing so, we are increasing the speed of our connection by adding an additional T-1.  We had two T-1’s each running to a different ISP but never really seemed to get effective use out of  both T-1’s using BGP as the routing protocol.  What is the best way of getting the best use out of our increased bandwidth?

— via the Internet

One way to do it would be to get all of your T-1’s converted into a fractional T3. This would mean that you would have only one interface on the router to configure for your Internet connection. 

But if that would cost more than maintaining multiple T-1’s, there is another option – if you’re using a Cisco router:

If all of the T-1’s go to the same POP from the ISP that you are using, see if the ISP will support Cisco Express Forwarding (CEF).  One of the features of CEF is that you can load balance on either per-destination or per-packet basis.  Implementation of CEF on a Cisco router can be as simple as putting

ip cef

into the router’s configuration.  If your T-1’s go to multiple POPs with the same ISP, they still might be able to go with CEF but you will need to talk to them about that.

I talked to Cisco about the way you were trying to use BGP for handling the routing with multiple T-1’s.  They responded that BGP isn’t a load-sharing option for multiple T-1’s.  It will help get the best route used when multiple T-1’s are present from more than one carrier. If you see one of the T-1’s is carrying more traffic than the others, you can “adjust” this by manually putting in routing statements in the router that override the route costs that are received by your router from the other routers at the ISP’s you are connecting to.