“… to share a single set of users/groups in LDAP to multiple samba
servers you will need LDAP and a PDC and the other servers will be
BDCs. yes you will join BDC’s with net rpc join -D domain -S
pdc_server_name -U root%password
read chapter 5.3 of samba 3 by example.pdf”

– Adam Williams
Source: http://lists.samba.org/archive/samba/2008-August/142551.html