Chapter 1. Connecting RHEL systems directly to AD using SSSD

You use SSSD to access a user directory for authentication and authorization through a common framework with user caching to permit offline logins. SSSD is highly configurable; it provides Pluggable Authentication Modules (PAM) and Name Switch Service (NSS) integration and a database to store local users as well as extended user data retrieved from a central server. SSSD is the recommended component to connect a RHEL system with one of the following types of identity server:

The most convenient way to configure SSSD to directly integrate a Linux system with AD is to use the realmd service. It allows callers to configure network authentication and domain membership in a standard way. The realmd service automatically discovers information about accessible domains and realms and does not require advanced configuration to join a domain or realm.

You can use SSSD for both direct and indirect integration with AD and it allows you to switch from one integration approach to another. Direct integration is a simple way to introduce RHEL systems to an AD environment. However, as the share of RHEL systems grows, your deployments usually need a better centralized management of the identity-related policies such as host-based access control, sudo, or SELinux user mappings. Initially, you can maintain the configuration of these aspects of the RHEL systems in local configuration files. However, with a growing number of systems, distribution and management of the configuration files is easier with a provisioning system such as Red Hat Satellite. When direct integration does not scale anymore, you should consider indirect integration. For more information about moving from direct integration (RHEL clients are in the AD domain) to indirect integration (IdM with trust to AD), see Moving RHEL clients from AD domain to IdM Server.

For more information about which type of integration fits your use case, see Deciding between indirect and direct integration.

You can directly integrate your RHEL system with Active Directory forests that use the following forest and domain functional levels:

Direct integration has been tested on the following supported operating systems:

By default, Identity Management establishes a cross-realm trust with support for RC4, AES-128, and AES-256 Kerberos encryption types. Additionally, by default SSSD and Samba Winbind support RC4, AES-128, and AES-256 Kerberos encryption types.

RC4 encryption has been deprecated and disabled by default, as it is considered less secure than the newer AES-128 and AES-256 encryption types. In contrast, Active Directory (AD) user credentials and trusts between AD domains support RC4 encryption and they might not support all AES encryption types.

Without any common encryption types, communication between RHEL hosts and AD domains might not work, or some AD accounts might not be able to authenticate. To address this situation, perform one of the configurations outlined in the following sections.

The System Security Services Daemon (SSSD) is the recommended component to connect a Red Hat Enterprise Linux (RHEL) system with Active Directory (AD). This section describes how to integrate directly with AD by using either ID mapping, which is the default for SSSD, or by using POSIX attributes.

Active Directory (AD) actively maintains its DNS records by timing out (aging) and removing (scavenging) inactive records.

By default, the SSSD service refreshes a RHEL client’s DNS record at the following intervals:

SSSD sends dynamic DNS updates to the AD server using Kerberos/GSSAPI for DNS (GSS-TSIG). This means that you only need to enable secure connections to AD.

The System Security Services Daemon (SSSD) service refreshes the DNS record of a Red Hat Enterprise Linux (RHEL) client joined to an AD environment at default intervals. The following procedure adjusts these intervals.

[domain/ad.example.com]
id_provider = ad
...

dyndns_update = false

If you set the id_provider = ad option in the /etc/sssd/sssd.conf configuration file, SSSD handles trusted domains as follows:

Active Directory (AD) forests can be very large, with numerous different domain controllers, domains, child domains and physical sites. AD uses the concept of sites to identify the physical location for its domain controllers. This enables clients to connect to the domain controller that is geographically closest, which increases client performance.

This section describes how SSSD uses autodiscovery to find an AD site to connect to, and how you can override autodiscovery and specify a site manually.

The realmd system has two major task areas:

In realmd use the command line tool realm to run commands. Most realm commands require the user to specify the action that the utility should perform, and the entity, such as a domain or user account, for which to perform the action.