Sites and services and queries for SRV records ...

Uri Simchoni uri at
Thu Sep 19 03:56:45 UTC 2019

On 9/18/19 10:18 PM, Richard Sharpe via samba-technical wrote:
> Hi folks,
> I thought, perhaps naively, that if an organization is using sites and
> services, and you do a query for SRV records from Site A for
> _ldap._tcp.<realm> that the Windows DNS servers would return the SRV
> records ordered with those for Site A first.
> Is there more that you have to do to ensure that? What I am seeing
> looks like standard random round-robin order.

The authoritative info on that is in [MS-ADTS] "Publishing an locating a 
domain controller". Central to that is the "LDAP Ping":
- In a large domain you'd get tens of DCs in response to your 
_ldap._tcp.<realm> query.
- You'd then send an "LDAP ping" - a UDP packet - to a bunch of them - 
Samba sends that in parallel, hoping some are not blocked by a firewall 
and will answer you.
- In the response, the DC indicates in which site you're on
- Then you make an SRV query specific to the site - 

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