Both the Replication Agent for DB2 UDB and ECDA Option for ODBC must use DB2 UDB client libraries. Cataloging configures an DB2 UDB client so that it knows how to connect to a particular database. Cataloging also creates a database alias, which Replication Agent or ECDA uses as the data source name.
By default, the client libraries are installed along with the DB2 UDB server. You can also separately install a DB2 UDB client on a host other than the one on which the server is installed. In either case, you must perform cataloging in the DB2 UDB client that Replication Agent or ECDA is using. If Replication Agent and ECDA are installed on different hosts, they are using different DB2 UDB clients, so the cataloging must be performed in both of the clients.
If the client and the server are on the same host, and there is only one DB2 UDB server running, cataloging may have been performed when the DB2 UDB instance was installed and the databases configured. If so, no additional cataloging is required.