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V4/Trust agents

Name: V4/Trust agents
Ticket: #4951
Target version: 4.2.0
Author: Ab
Green tick.png Reviewed by: Sbose
Last updated: 2015-07-24 by Ab

Overview

FreeIPA supports trusted relationships with Active Directory via cross-forest trust. Currently all functionality to support trusted relationships with Active Directory must be present on every IPA master which controls IPA clients where access to AD users is desired. There is certain difference between uses of the IPA infrastructure which allow to reduce requirements towards IPA masters involved in providing trust features.

A trust controller is a FreeIPA master which runs following services:

  • LDAP server with sigden, extdom, and cldap plugins
  • KDC with IPA driver
  • Samba configured with ipasam PASSDB module
  • SSSD with ipa_server_mode=True
  • Global Catalog instance (a separate LDAP instance with an AD-compatible schema)

A trust agent is a FreeIPA master which runs following services

  • LDAP server with sigden and extdom plugins
  • KDC with IPA driver
  • SSSD with ipa_server_mode=True

Trust agent is a master that relies on SSSD to do resolution of IDs. Trust controller is used for managing trust: add trust agreements, enable/disable separate domains from a trusted forest to access FreeIPA resources, etc. Trust controller is also what Active Directory's domain controllers contact when validating the trust by means of SMB protocol using LSA calls which implies running a Samba server.

Use cases

Two major use cases are:

  • IPA replicas are used to resolve AD users and groups but not used to administer trust (trust agents)
  • IPA replicas are used to establish trust and manipulate their properties

In case of trust agent, not running Samba suite reduces exposure for possible security breaches. Additionally, such lightweight IPA replica reduces possibility to negatively influence performance when trust is validated as it will not be used by AD DCs to contact to validate trust. AD DCs consider IPA replicas to contact based on DNS SRV records. If lightweight IPA replica is not present in the corresponding MSDCS SRV record, it will not be contacted and thus possible replication delays will not cause validation issues. This is an important consideration because currently FreeIPA does not have concept of sites and site-local communication.

Design and Implementation

Primary ticket: https://fedorahosted.org/freeipa/ticket/4951 No major code changes required, only defaults need to be changed on which plugins are enabled and how they are used.

In order to support trust agents role, FreeIPA has changes ipa-adtrust-install tool and updates to convert existing IPA masters without ipa-adtrust-install into the ones that enable extdom and sidgen plugins if any of ipa-adtrust-install artefacts are in the replicated tree.

Running ipa-adtrust-install --add-agents at the IPA master which handles trust setup is required to convert specific IPA masters. There is now no need to run ipa-adtrust-install utility on all IPA masters, it should be run only on those masters where trust is supposed to be established.

Additionally, RPM dependencies need to change to allow installing Samba libraries which are in use by SSSD components and extdom/sidgen plugins.

Enablement of slapi-nis to provide AD users' access should depend on whether compat tree is enabled at this IPA master already or not.

Feature management

CLI

no changes

Web UI

no changes

Replication

no changes

Upgrades

Upgrade code automatically enables sidgen and extdom plugins.