CA Directory r12.0 SP1 and later caters for the LDAP Server Side Sorting control by default when connecting directly to the data DSA that has the information required. There is a specific use case that deals with Router and data DSA's (used in a highly available DSA backbone). This techdoc discusses that high availability use case.
From r12.0 SP1 onwards, the LDAP Server Side Sorting control (1.2.840.1135188.8.131.523) is available when connecting directly to the data DSA to be searched.
In addition to directly connecting to the data DSA, the control is also supported when used in distributed directory backbones (e.g. submit a search to a router DSA that then routes the operation to a data DSA for execution). But please be aware that there is a very specific use case where a server side sorting control is supported when dealing with routers and data DSAs.
The two main use cases for distributed searching are:
Router receives a whole subtree search that has a base DN that falls within a remote data DSAs namespace (prefix)
Router receives a whole subtree search that has a base DN that falls within the routers namespace (prefix)