When you setup directory replication, the export server defaults to exporting to the local domain. The export server broadcasts mailslots addressed to \MAILSLOT\NET\REPL_CLI which are sent on subnet of the export server. These broadcasts are not forwarded across a router or bridge.
To work around this problem, add the NetBIOS name of the the import computer to the To List on the export server. This NetBIOS name will be resolved and the mailslot addressed to \MAILSLOT\NET\REPL_CLI will be sent to the import computers in the To List.
See tip 609.