Can't Touch This: Consistent Network Updates for Multiple Policies

Computer networks such as the Internet or datacenter networks have become a a crucial infrastructure for many criticial services. Accordingly, it is important that such networks preserve correctness criteria, even during transitions from one correct configuration to a new correct configuration. This paper initiates the study of how to simultaneously update multiple routes in a Software-Defined Network (SDN) in a transiently consistent and efficient manner. In particular, we study the problem of minimizing the number of switch interactions, in this paper also called "touches". Our main result is a negative one: we rigorously prove that jointly optimizing multiple route updates in a consistent and efficient manner is NP-hard, alreadyfor two routing policies. However, we also present an efficient, polynomial-time algorithm that, given correct update schedules for individual policies, computes an optimal global schedule with minimal touches.