[Freeipa-users] IPA trust integration in AD Forests that been upgraded to higher functional level

Sat Jan 3 03:13:07 UTC 2015

Hello all.

I'm working on integrating AD trust feature in the forest of a large
organization (Its network is not connected to the internet).

First I tested the trust in "clean" environment (that i have deployed) to
simulate production forest deployment , in the following configuration:

The forest root domain  : red.com

Second Domain tree      : blue.com

IPA                             : linux.blue.com

All the AD DCs are 2008 R2 server and 2008 R2 functional level.

IPA server in installed on RHEL 7.

ipa-server-3.3.3-28.el7_0.1.x86_64

ipa-server-trust-ad-3.3.3-28.el7_0.1.x86_64

ipa-python-3.3.3-28.el7_0.1.x86_64

With help of the mailing list, all works fine. Users from both red.com and
blue.com are able to log into IPA domain.

After the success, I proceeded to test the trust in organization's test
environment.

The installation of the trust itself has completed successfully. But
although users from *red.com <http://red.com>* were able to log into IPA
domain, users from *blue.com <http://blue.com>* couldn't.

After checking the sssd logs it seemed as blue.com domain is unknown to IPA.

Therefore I ran "*ipa trustdomain-find red.com <http://red.com>" *in both
environments, to see if there are any differences.

And indeed there were:

While in the "clean" environment,  the command returned both *red.com
<http://red.com>* and *blue.com <http://blue.com>* domains, in
organization's test environment it returned only *red.com <http://red.com>*.

I tried to re fetch the domain with "*ipa trust-fetch-domains red.com
<http://red.com>" *but it returned the message - " No new trust domains
were found".

It made me think that maybe the AD is not returning all domains in the
forest.

I opened wireshark on both environments and ran  "*ipa trust-fetch-domains
red.com <http://red.com>" *to see what is been sent from AD to IPA.

In both environments I seen the DsrEnumerateDomainTrusts request and
response.

Reading the content of response showed that in both environments, the
response contained *red.com <http://red.com>* and *blue.com
<http://blue.com>* domain.

After inspecting the structures that contain domains information
(DS_DOMAIN_TRUSTS)  , I noticed that in both environments the *TrustAttribute
*of red.com is set to 0x0000000.

But *TrustAttribute *of blue.com is set to 0x00000020 (
TRUST_ATTRIBUTE_WITHIN_FOREST) in the "clean" environment and  to
0x00800000 in the test environment.

Reading MSDN for *TrustAttribute*, explains the following:

http://msdn.microsoft.com/en-us/library/cc223779.aspx

(TRUST_ATTRIBUTE_WITHIN_FOREST)

0x00000020

If this bit is set, then the trusted domain is within the same forest.

Only evaluated on Windows Server 2003, Windows Server 2008, Windows
Server 2008 R2, Windows Server 2012, and Windows Server 2012 R2.

While I couldn't find specific information about 0x00800000, but this:

0x00400000 - 0x00800000

Previously used trust bits, and are obsolete.

I did not find more information on 0x00800000 or a reason why the
attributes would be different in the two deployments.

I asked for advice from Microsoft IT guy in the organization. He said that
difference in the *TrustAttribute *is caused by the fact, that the "clean"
environment was created as Windows Server 2008, while the test (and
production) forest was created as windows 2000 servers (about  12 years
ago) and the forest was gradually upgraded to 2003 and 2008 along the years.

Couldn't find more information on the attribute for windows server
2000/2003 but the theory sounds quite logical.

I decided  to check if *TrustAttribute *influences IPA's domain fetch.

fetch_domains function in
/usr/lib/python2.7/site-packages/ipaserver/dcerpc.py

contains the following lines of code:

    trust_attributes = dict(

                NETR_TRUST_ATTRIBUTE_NON_TRANSITIVE     = 0x00000001,

                NETR_TRUST_ATTRIBUTE_UPLEVEL_ONLY       = 0x00000002,

                NETR_TRUST_ATTRIBUTE_QUARANTINED_DOMAIN = 0x00000004,

                NETR_TRUST_ATTRIBUTE_FOREST_TRANSITIVE  = 0x00000008,

                NETR_TRUST_ATTRIBUTE_CROSS_ORGANIZATION = 0x00000010,

                NETR_TRUST_ATTRIBUTE_WITHIN_FOREST      = 0x00000020,

                NETR_TRUST_ATTRIBUTE_TREAT_AS_EXTERNAL  = 0x00000040)

.

.

.

result = []

    for t in domains.array:

        *if ((t.trust_attributes &
trust_attributes['NETR_TRUST_ATTRIBUTE_WITHIN_FOREST']) and*

*            (t.trust_flags & trust_flags['NETR_TRUST_FLAG_IN_FOREST'])):*

            res = dict()

            res['cn'] = unicode(t.dns_name)

            res['ipantflatname'] = unicode(t.netbios_name)

            res['ipanttrusteddomainsid'] = unicode(t.sid)

            res['ipanttrustpartner'] = res['cn']

            result.append(res)

The bit-wise operation is preformed to check if the trust attribute is set
to TRUST_ATTRIBUTE_WITHIN_FOREST  (0x00000020) and if so, the trust is
added to result array.

It seems the value of *TrustAttribute *set to 0x00800000 is the reason the
domain wasn't fetched.

To confirm it I changed the if statement to:

        if ((t.trust_attributes &
trust_attributes['NETR_TRUST_ATTRIBUTE_WITHIN_FOREST'] *|| *

*(t.trust_attributes & 0x00800000)) *and (t.trust_flags &
trust_flags['NETR_TRUST_FLAG_IN_FOREST'])):

Then deleted and recreated the trust and finally ran "*ipa
trust-fetch-domains red.com <http://red.com>"-*

this time the *blue.com <http://blue.com>* domain did appear!

I was able to login with users from both red.com and blue.com to IPA domain.

Checking both upstream 3.3 and 4.1 shows that the if statement was changed
to :

*if* (*not* (t.trust_flags & trust_flags['NETR_TRUST_FLAG_PRIMARY']) *and*

            (t.trust_flags & trust_flags['NETR_TRUST_FLAG_IN_FOREST'])):

https://git.fedorahosted.org/cgit/freeipa.git/tree/ipaserver/dcerpc.py?h=ipa-3-3#n1039

https://git.fedorahosted.org/cgit/freeipa.git/tree/ipaserver/dcerpc.py?h=ipa-4-1#n1102

>From first sight it looks like blue.com will fetched.

Haven't yet tested if upstream works in the test environment.

Any thoughts on the subject will be great.

(I hope i'm not mentioning something that was solved long ago).

Genadi
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