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

[Kris Lou]

Here is another link (with a set of links in the article, sorry):
https://blogs.msmvps.com/acefekay/2010/01/03/the-dc-locator-process-the-logon-process-controlling-which-dc-responds-in-an-ad-site-and-srv-records/


I particularly like the Summary graphic about 20% down:

   1. New client queries for all DCs in the domain
      - Retrieves SRVs from _tcp.<domain>
   2. Attempts LDAP bind to all
   3. First DC to respond
      - Examines client IP and subnet definitions
      - Refers client to a site
   4. Client stores site in registry
   5. Client queries for all DCs in the site
      - Retrieves SRVs from _tcp.<site>._sites.<domain>
   6. Attempts LDAP bind to all
   7. First DC to respond
      1. Authenticates client
      2. Client forms affinity
   8. Subsequently
      - Client binds to affinity DC
      - DC offline? Client queries for DCs in registry-stored site
      - Client moved to another site? DC refers client to another site (see
      #4)

Now, I haven't observed all of this in an offline DC situation, but
"winbind --ping-dc" will show the equivalent to "nltest /dsgetdc:<domain>
/gc" to show the DC currently being queried.


Kris Lou
klou at themusiclink.net


On Fri, Jan 31, 2020 at 8:05 AM Paul Littlefield via samba <
samba at lists.samba.org> wrote:

> On 31/01/2020 13:15, Rowland penny via samba wrote:
> > Each DC should use itself as its DNS nameserver, but your clients should
> be able to use any DC for their DNS nameserver. You need to consult your
> OS's documentation to see how DNS failover should be set up. That is, if
> your client attempts to contact a particular DNS server running on a DC and
> it doesn't answer, it goes to the next DC DNS server without any real delay.
>
> Sorry, forgot to say that both DCs have themselves and each other in
> /etc/resolv.conf
>
> Regards,
>
> Paul
>
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