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The Border Gateway Protocol (BGP) is a unique routing protocol in broadband Internet. It chooses routing paths considering Internet hierarchy and local policies. In BGP connectivity by way of a series of links between source and destination nodes does not mean reachability between the two. At emergency when BGP routers or links over wide range are not available, BGP routers have to use links that are not normally used to keep reachability. This paper lists the requirements for BGP backup routing and proposes a routing solution, which operates differently according to network damage. At normal BGP routers choose level-0 routes. If networks are impaired, they can choose level-1 paths. Level-2 paths are only used under serious damage. Also this paper proves that the proposed backup guarantees stability and safeness. As results, the proposed backup is much adaptive to light network damages as well as serious ones and provides strong routing reachability at all times.