Sumit,

AD administrators maintain the relationship between subnet and sites in the "AD Sites and Services" administrative tool.

They associate particular subnets with a particular site there.  From your URL, it appears that the client sends its IP address in its CLDAP query.  The AD DC does the subnet math and looks up the matching site in the AD Sites and Services data  (most specific matches matches first, then more general).  

Our AD team has an ultimate back-stop of 0.0.0.0/1 and 128.0.01/1  (most general), I think aka "CompanyGeneral". 

It sounds like a lot of work, but if they logically group their IP addresses so that they can use big supranets (say 10.0.0.0/9 for siteA and 10.128.0.0./9 for siteB), it's not so much manual effort.

I would guess that AD sites and services lookups wouldn't work across forests;  which forest would be authoritative?  If you're searching your local forest, with ultimate back-stops of above you'd always find a site in your local forest and never traverse to another forest.

Spike

On Fri, Jun 24, 2022 at 4:22 AM Sumit Bose <sbose@redhat.com> wrote:
Am Thu, Jun 23, 2022 at 10:24:33AM -0600 schrieb Orion Poplawski:
> The docs seem a little unclear to me on this.  They note what when using the
> AD provider sssd will perform site discovery to find the closest AD
> controller.  But what about when using the IPA provider?  It seems to me like
> it doesn't, and if not - why not?

Hi,

afaik site discovery does not work across forest boundaries. To my
knowledge AD DCs determine the site based on IP addresses given out by
the DCs via DHCP, so only the DC of the domain you are joined to can
return the site reliable. There is the concept of NextClosestSiteName
(see MS-ADTS 6.3.3.2
https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-adts/3d71aefb-787e-4d14-9a8a-a70def9e1f6c)
but I'm not sure if this would give more reliable results. Based on this
we decided that if might be better to set the site explicitly in
sssd.conf.

Please let me know if you are aware of additional documentation which
covers sites across forest boundaries.

HTH

bye,
Sumit

(I posted the same reply to your question in
https://github.com/SSSD/sssd/issues/5958)

>
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