[Samba] Failover DC did not work when Main DC failed

[Paul Littlefield]

On 18/02/2020 19:58, Kris Lou via samba wrote:
> This might be a problem down the road.  The Samba Internal DNS does NOT
> round-robin -- it will always return your list of DC's in the same order,
> so requests usually go to the first result.  If you have any simple
> ldapclients (PHP clients, for example), it will query in order.  I don't
> know if the ldapclient is smart enough to look at a 2nd DNS response if the
> 1st doesn't respond, but probably not -- further implied by "password
> server = <dc1> <dc2>" and failover/redundancy is handled sequentially.
> 
> Re-reading how Windows' Netlogon Cache and such works, the client should
> query a DNS server for known DC's and then perform an ldap-ping to ALL of
> them before caching the preferred DC.  Which should mean that the order in
> which a DC is listed or returned shouldn't matter, so the Internal DNS
> lacking round-robin shouldn't matter to Windows clients.  But you might as
> well go all the way ...


Hello Kris,

Thanks for this information, hopefully it will help us.


Samba 4 AD DC
QNAP Domain Joined

DNS1 = 192.168.0.218
DNS2 = 192.168.0.219
DC1 = 192.168.0.218
DC2 = 192.168.0.219
QNAP = 192.168.0.201


So, normally, a Windows client should do this...

Domain --> DNS1 --> DC1
Files --> DNS1 --> QNAP --> DC1


In the event of server failure (DNS1/DC1 is unavailable) a Windows client should do this...

Domain --> DNS1 = fail
        --> DNS2 --> DC1 = fail
                 --> DC2

Files --> DNS1 = fail
       --> DNS2 --> QNAP --> DC1 = fail
                         --> DC2


...have I got that correct?

Is this what everyone else is doing?!

Regards,

Paully

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