[Samba] LDAP master-slave and BDC ?

John H Terpstra jht at Samba.Org
Fri May 20 03:09:54 GMT 2005

On Thursday 19 May 2005 20:04, Msdigital wrote:
> I am a bit confused, about the LDAP master-slave and BDC. I have an
> Samba-LDAP server that serves as my PDC. All my users authenticate to this
> server. I would like to set up a BDC for failover. What is the difference
> between a BDC and a LDAP Slave server?

A BDC is a NT4 domain controller that handles network logon authentication.
A Samba BDC will relay all network account updates to a PDC. Only the PDC will 
write to the passdb backend. A BDC will read authentication data from the 
passdb backend it is configured to use.

A Slave LDAP server is a read-only mirror of an LDAP Master server. A PDC 
would normally be directed at a Master LDAP server, but can work with a Slave 
LDAP server. If a PDC is configured to use a Slave LDAP server all write 
requests to the directory will be handled via a referral to the Master LDAP 
server. In other words, all write requests are handled by the Master LDAP 

It does not matter whether a BDC uses a Master or a Slave LDAP server - it 
only ever reads directory information from it.

What do you mean by fail-over? A BDC can handle network logon requests, but it 
can never replace a PDC. In other words, the PDC is still the weakest link. 
If a PDC is off the air for a prolonged outage the network will eventually 

> Second part.
> Does anyone on this list have this type of configuration, PDC-BDC or
> Master/Slave and can help do the same?

Please refer to the book: "Samba-3 by Example" Chapters 5 and 6. You can 
obtain a copy from:



- John T.
John H Terpstra
Samba-Team Member
Phone: +1 (650) 580-8668

The Official Samba-3 HOWTO & Reference Guide, ISBN: 0131453556
Samba-3 by Example, ISBN: 0131472216
Hardening Linux, ISBN: 0072254971
Other books in production.

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