We study a problem motivated by a scheme for supporting fast  
restoration in MPLS and optical networks. In this local restoration
scheme detour paths are set-up a priori and network resources are
pre-reserved exclusively for carrying rerouted traffic under network
failures. (i.e. they do not carry any traffic under normal working
conditions). The detours are such that failed links can be bypassed
locally from the first node that is upstream from the failures. This  
local bypass activation from the first detection point for failures
along with the dedication of network resources for handling failures
permits very fast recovery times, a critical requirement for these
networks. By allowing sharing of the dedicated resources among
different detours the local restoration scheme results in efficient
utilization of the pre-reserved network capacity.

In this paper we are interested in the problem of dedicating the least
amount of the currently available network capacity for protection, 
while guaranteeing fast restoration to the existing traffic along with
any traffic that may be admitted in the future. We show that the   
problem is NP-hard, and give a 2-approximation algorithm for the
problem. We also show that the integrality gap of a natural relaxation
of our problem is Omega(n), thus establishing that any LP-based
approach using this relaxation cannot yield a better approximation 
algorithm for our problem.