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Load-balancing

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by nict

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Currently we are having 8xE1s running to 2 different ISPs. 4xE1s to each of them. The frist 4 links were established about 2 years ago and connected to 1 ISP. Due to congestion, we add 4 more links but to different ISP. All 8 links are running on BGP. The load balancing on the first 4 links are working fine but the load-balance on the additional 4 links are not working. At the same time, the traffics are not load-balancing to both ISPs. The first 4 links are still 98 percent utilised while the additional 4 links are only 20 percent utilised. I've tried prepending the AS numbers but it doesnt seems to work.

Can anyone help me in this issue.

Thank you

3 replies

by Former member

BGP load balancing success, no matter how you prepend, depends upon the return traffic from the ISP. All ISPs not being created equally, you should have at least control over the outbound traffic by prepending. Whenever you choose ISPs, you must remember that the return traffic will take the shortest route. The shortest route depends on the ISP. Smaller ISPs have more hops...etc, so that path will not be chosen (unless a link goes down with the larger one). So I suspect your problem is due to using "smaller" ISPs.

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