This is the relative name distinguishing this switch-side internal link record from its siblings under the same fabric interconnect. It matters on the same internal chassis backplane link, but the record kept on the Fabric Interconnect (switch) side rather than the IOM/server side because the fabric interconnect tracks a separate record per backplane link it terminates, and this rn is what differs between them. An rn identifying port 13 on this link's fabric-interconnect side distinguishes this specific switch-side backplane connection from the fabric interconnect's other chassis connections.