olcServerID: 1 ldap://ldap1
olcServerID: 2 ldap://ldap2
olcServerID: 3 ldap://ldap3
1. you should probably use FQDNs instead of short names
2. you must explicitly start slapd to -h ldap://ldap1 etc. to really assign
the server-ID to a certain replica.
BTW: Personally I prefer to not replicate cn=config (I'm using static
configuration anyway) and just add one server ID per instance to avoid the
strong dependency on -h option.