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A link load balancer, also called a link balancer, is a network appliance that distributes in-bound and out-bound traffic to and from multiple Internet Service Provider (ISP) links. Link load balancers are typically located between gateway routers and the firewall.
To ensure maximum uptime, many enterprise networks lease two or more ISP links. One of the links connecting the company’s internal network to the ISP acts as a backup. Paying for a link that is rarely used is an inefficient use of bandwidth, however.
A link load balancer uses traffic management algorithms to ensure that all leased ISP links are being used to their best advantage. The network administrator sets policies for the appliance so when it receives a request, it takes into account such things as client and end-user round-trip times and which ISP link has the most available bandwidth before completing the request.
See also: Border Gateway Protocol (BGP)