samba - Jan 2013 - Samba member server and trusted domains question

Hi,

I have two Windows Domains, DOMA and DOMB. A Samba 3.6 Server is a member server
in DOMA.
DOMA has a (unidirectional) trust relationship to DOMB.
Users from DOMB should be able to connect and authenticate at the Samba server.

The domain controller of DOMB has the IP 10.35.5.25.

During authentication of a DOMB user at a share I get the following log entries:

  get_dc_list: preferred server list: ", *"
[2013/01/10 11:24:59.816974,  3] libads/ldap.c:640(ads_connect)
  Successfully contacted LDAP server 10.35.5.25
[2013/01/10 11:24:59.818216,  3] libads/ldap.c:640(ads_connect)
  Successfully contacted LDAP server 10.35.5.25
[2013/01/10 11:24:59.819284,  3] libads/ldap.c:694(ads_connect)
  Connected to LDAP server dc01.domb
[2013/01/10 11:24:59.821064,  3] libads/sasl.c:869(ads_sasl_spnego_bind)
  ads_sasl_spnego_bind: got OID=1.2.840.48018.1.2.2
[2013/01/10 11:24:59.821196,  3] libads/sasl.c:869(ads_sasl_spnego_bind)
  ads_sasl_spnego_bind: got OID=1.2.840.113554.1.2.2
[2013/01/10 11:24:59.821296,  3] libads/sasl.c:869(ads_sasl_spnego_bind)
  ads_sasl_spnego_bind: got OID=1.2.840.113554.1.2.2.3
[2013/01/10 11:24:59.821354,  3] libads/sasl.c:869(ads_sasl_spnego_bind)
  ads_sasl_spnego_bind: got OID=1.3.6.1.4.1.311.2.2.10
[2013/01/10 11:24:59.821478,  3] libads/sasl.c:878(ads_sasl_spnego_bind)
  ads_sasl_spnego_bind: got server principal name = dc01$@DOMB
[2013/01/10 11:24:59.822188,  3] libsmb/clikrb5.c:787(ads_krb5_mk_req)
  ads_krb5_mk_req: krb5_cc_get_principal failed (No credentials cache found)
Ignoring unknown parameter "idmap domains"
[2013/01/10 11:25:00.883025,  1] libsmb/clikrb5.c:799(ads_krb5_mk_req)
  ads_krb5_mk_req: smb_krb5_get_credentials failed for ldap/dc01.domb at DOMB
(Server not found in Kerberos database)
[2013/01/10 11:25:00.883184,  0] libads/sasl.c:908(ads_sasl_spnego_bind)
  kinit succeeded but ads_sasl_spnego_krb5_bind failed: Server not found in
Kerberos database
[2013/01/10 11:25:00.883536,  1]
winbindd/idmap_ad.c:149(ad_idmap_cached_connection_internal)
  ad_idmap_cached_connection_internal: failed to connect to AD

First you have to know that the users can successfully authenticate to the samba
server. But there are error messages in the log I don?t understand, especially
the "failed to connect to AD" error message.
Why is this AD connection to DOMB necessary? What exactly is the samba server
trying to do with the DOMB domain controller?

Kind regards

Carsten