Most customers are usually not comfortable with a 1-phase migration approach for their Directory Service. This is especially true for banks.
As such, usually, the Parallel Migration approach is adopted. This approach has the old and new Directory Servers running in parallel. Applications will be migrated one-at-a-time from utilizing the old Directory Server to the new one.
While the Parallel Migration is in process, there is a need for 2-way replication between the old and new Directory Servers. This ensures the data integrity.
2-way replication can only be configured for the following versions
1. DS 5.2 <-> DS 6.x
2. DS 5.2 <-> DS 7.0
3. DS 6.x <-> DS 7.0
Sun Directory Server 5.1 cannot replicate directly with 6.x and 7.0, due to difference in schema.
A local customer was having the 5.1 version and they wanted to upgrade to 6.3.1. We had to configure the replication as such:
DS 5.1 <-> DS 5.2 <-> DS 6.3.1