Improved network design techniques are provided. More particularly, the invention provides network design techniques that support fast restoration. In one aspect of the invention, a technique for designing a protection capacity to be reserved in a network comprises the following steps/operations. Link capacities associated with a network topology and existing working traffic in the network are obtained. Capacity partitions are determined for links in the network topology. Each of at least a portion of the capacity partitions comprise a protection capacity portion and a working capacity portion that equals or exceeds the existing working traffic on a corresponding link, such that upon a failure on the link, the working traffic on the link is rerouted over a pre-provisioned detour path using the protection capacity portion on one or more links on the detour path. Further, the capacity partition determination step/operation substantially guarantees protection for existing working traffic in the network. Still further, the capacity partition determining step/operation may further substantially guarantee protection for future working traffic in the network.