On ti, 15 kesä 2021, Ronald Wimmer via FreeIPA-users wrote:
On 15.06.21 07:39, Alexander Bokovoy via FreeIPA-users wrote:
>On ma, 14 kesä 2021, Ronald Wimmer wrote:
>>On 14.06.21 13:37, Alexander Bokovoy wrote:
>>>On ma, 14 kesä 2021, Ronald Wimmer via FreeIPA-users wrote:
>>>>On 12.06.21 13:08, Florence Renaud via FreeIPA-users wrote:
>>>>>please refer to External Trusts to Active Directory  from
>>>>>WIndows Integration guide, it nicely explains the difference
>>>>>between external trust and forest trust.
>>>>Sorry for my unspecific initial question. I did read the
>>>>documentation. As I understood it the external trust somehow
>>>>isolates the view on that particular domain.
>>>>If DomA_Trust is a normal one and DomB_Trust an external one I
>>>>cannot use DomB users in a DomA group for example, right? If
>>>>DomB trust was not external I could do that?
>>>I think you need to start with Active Directory design and
>>>documentation. In particular, group types in AD define who can be
>>>included into them and how they can be consumed:
>>>Type of trust between domains influences the use of groups but group
>>>scopes are ultimate ones here.
>>>When applying that to a trust between IPA and AD, remember that we only
>>>have two trust types:
>>> - forest trust: IPA domain is in a separate forest than any AD domain
>>> - external trust: only immediately trusted AD domain users and groups
>>> can be seen and used for authentication across the trust, there is no
>>> transitivity into any other trust that this AD domain may have
>>> anywhere else
>>>In addition to that, while forest trust in itself is transitive to
>>>domains in the trusting forest, there is no transitivity across all
>>>trusting forests. If forest A trusts forest B and forest B trusts forest
>>>C, there is no trust from forest A to any domain in forest C.
>>>The same applies to groups from those forests as well, complicated by
>>>the group scopes.
>>In our case IPA hast a trust to the forest root of domain A which
>>itself has a trust to domain B. IPA has an external trust to
>>domain B. With the AD management tool we are using I can put users
>>of domain B into a group of domain A.
>What matters is where domain B is located. Is it part of the same forest
>as domain A? Is it outside of forest A?
It is outside of forest A but forest A has a trust to it.
As I already said, forest trust is not transitive to other forest
trusts. So it does not count, a trust to B has to be explicitly created.
>>When I try to use that particular group (POSIX group that has
>>AD group as its member) in a HBAC scenario I do get a permission
>It can be anything. This information does not give any chance to
>understand why there is a problem.
At the moment I do have users of domain B in a group of domain A. I
cannot use that particular group in IPA. I think this could be because
I setup the IPA trust to domain B as external.
Check the first link I gave. Only 'domain local' groups can include
members from "Accounts, Global groups, and Universal groups from other
forests and from external domains". Domain local groups, on the other
hand, can only be used inside the domain they defined.
Thus, such groups cannot be used over a trust to IPA.
>>External trust to domain B was setup years ago when we were
>>experimenting with IPA. So my first question is if the separate
>>trust to domain B is needed at all? (because there is a trust from
>>domain A to domain B on the AD side.) If yes I probably would not
>>want domain B trust to be an external one in my scenario, would I?
>You need to decide what you want. ;) If A and B are in the same forest,
>then you don't need an external trust to B from IPA side.
If I want to use users of domain B in a domain A group I will probably
have to set up a 'normal' trust to domain B and not an 'external' one.
Do you agree?
No. It does not matter. What matters is a group type. If you have group
members from outside your own forest, you can only use them in domain
local groups but these groups then cannot be used in other forests or
even within your own forests but in other domains. This is Active
Directory's design limitation.
What you could do is to have a trust in IPA to both forest A and a
domain B, then have IPA external groups that include individually
users/groups from A and B, then use IPA POSIX groups to include IPA
external groups. Those IPA POSIX groups then can be used to apply
permissions on IPA side.
/ Alexander Bokovoy
Sr. Principal Software Engineer
Security / Identity Management Engineering
Red Hat Limited, Finland