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Ethernet ring protection (ERP) has recently emerged to provide protection switching for Ethernet ring topologies with sub-50-ms failover capabilities. ERP's promise to also provide protection in multi-ring mesh packet transport networks will position Ethernet as a serious competitor to conventional synchronous optical networking (SONET)/synchronous digital hierarchy (SDH) and the technology of choice for carrier networks. Operating ERP in multi-ring mesh networks, however, comes with unique challenges. This paper reveals some limitations of prior work which relied on exhaustive enumeration and proposes some modifications to overcome these subtle limitations. We also present an optimal ERP design formulation by jointly solving the problem of ring protection link placement and ring hierarchy selection whose objective is to minimize the overall capacity requirement. Our design approach is formulated as an integer linear program, which is shown to provide optimal capacity provisioning and be computationally scalable.