This paper addresses the problem of inter-domain QoS routing with Service Level Agreements (SLA) for data transport between peering domains, using virtual-trunk type aggregates. The problem is formally stated and formulated in Integer Linear Programming. As a practical solution, we define the QoS_INFO extension to the BGP routing protocol, conveying three different QoS metrics (light load delay, assigned bandwidth and a congestion alarm), and a path selection algorithm using a combination of these metrics. We present simulation results of QoS_INFO, standard BGP, and BGP with the QoS_NLRI extension, and compare them with the optimal route set provided by the ILP formulation. The results show that our proposal yields better QoS than standard BGP or BGP with the QoS_NLRI extension, since it is able to efficiently avoid congested paths, and that the impact of QoS_INFO in route stability is relatively low.