3.7.d Implement, optimize and troubleshoot routing policies

3.7.d [v] Multi-homing

Border Gateway Protocol ( BGP) is one of the key protocols to use to achieve Internet connection redundancy. When you connect your network to two different Internet service providers (ISPs), it is called multi-homing. Multi-homing provides redundancy and network optimization. It selects the ISP which offers the best path to a resource. When you are running BGP with more than one service provider, you run the risk that your autonomous system (AS) will become a transit AS. This causes Internet traffic to pass through your AS and potentially consume all of the bandwidth and resources on the CPU of your router.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 3999-4003).  . Kindle Edition.

http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/23675-27.html