This paper initiates the study of fault resilient network structures that mix two orthogonal protection mechanisms: (a) backup, namely, augmenting the structure with many (redundant) low-cost but fault-prone components, and (b) reinforcement, namely, acquiring high-cost but fault-resistant components. To study the trade-off between these two mechanisms in a concrete setting, we address the problem of designing a (b, r) fault-tolerant BFS (or (b, r) FT-BFS for short) structure, namely, a subgraph H of the network G consisting of two types of edges: a set E ⊆ E of r(n) fault-resistant reinforcement edges, which are assumed to never fail, and a (larger) set E(H) \ E of b(n) fault-prone backup edges, such that subsequent to the failure of a single fault-prone backup edge e ∈ E \ E , the surviving part of H still contains a BFS spanning tree for (the surviving part of) G, satisfying dist(s, v, H \ {e}) ≤ dist(s, v, G \ {e}) for every v ∈ V and e ∈ E\E . We establish the following tradeoff: For every real ∈ (0, 1], if r(n) =Θ(n 1− ), then b(n) =Θ(n 1+ ) is necessary and sufficient. More specifically, as shown in [14], for = 1, FT-BFS structures (with no reinforced edges) require Θ(n 3/2 ) edges, and this is sufficient. At the other extreme, if = 0, then n − 1 reinforced edges suffice (with no need for backup). Here, we present a polynomial time algorithm that given an undirected graph G = (V, E), a source vertex s and a real ∈ (0, 1], constructs a (b(n), r(n)) FT-BFS with r(n) = O(n 1− ) and b(n) = O(min{1/ · n 1+