Griffin, Jaggard, and Ramachandran introduced a framework for studying design principles for path-vector protocols, such as the Border Gateway Protocol (BGP) used for inter-domain routing in the Internet. They outlined how their framework could describe Hierarchical-BGP-like systems in which routing at a node is determined by the relationship with the next-hop node on a path (e.g., an ISP-peering relationship) and some additional scoping rules (e.g., the use of backup routes). The robustness of these class-based path-vector systems depends on the presence of a global constraint on the system, but an adequate constraint has not yet been given in general. In this paper, we give the best-known sufficient constraint that guarantees robust convergence. We show how to generate this constraint from the design specification of the path-vector system. We also give centralized and distributed algorithms to enforce this constraint, discuss applications of these algorithms, and compare them to algorithms given in previous work on path-vector protocol design.