Abstract—We present a distributed routing algorithm for finding two disjoint (primary and backup) QoS paths that run across multiple domains. Our work is inspired by the recent interest in establishing communication paths with QoS constrains spanning multiple IP/MPLS domains. In such settings, the routing decisions in each domain are made by the Path Computation Element (PCE). We assume that the PCEs run a joint distributed routing protocol, decoupled from the BGP, which enables them to establish efficient paths across multiple domains. This study makes the following contributions. First, we present an aggregated representation of a multi-domain network that is small enough to minimize the link-state overhead, and, at the same time, is sufficiently accurate, so that the PCEs can find optimal disjoint QoS paths across multiple domains. Second, we present a distributed routing algorithm that uses the proposed representation to find disjoint paths in an efficient manner. Finally, ...