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DNS

FreeIPA DNS integration allows administrator to manage and serve DNS records in a domain using the same CLI or Web UI as when managing identities and policies. At the same time, administrator can benefit from the tight DNS integration in FreeIPA management framework and have configuration changes in FreeIPA server covered by automatic DNS updates (see next chapters for more detailed list of benefits).

Initial Considerations

The DNS component in FreeIPA was designed and built about several basic assumptions and goals that should be always considered when assessing enhancements or other requests to this component.

Assumptions

  • DNS is hard to manage and lot of admins who want to deploy FreeIPA would have difficulties setting up DNS properly.
  • DNS is central to have a decent Kerberos experience.
  • Single-master DNS is error prone, especially for inexperienced admins.

Goals

  • Provide an integrated DNS server which can be used to ease FreeIPA deployment ("get you going").
    • Provide ability to standup and tear down replicas without caring for the special "master" DNS server.
  • Provide an alternative option for users with existing DNS infrastructure: Provide means for integrating FreeIPA with existing DNS infrastructure.
  • Goal is NOT to provide general-purpose DNS server. Features beyond easing FreeIPA deployment and maintenance are explicitly out of scope.

Benefits of integrated DNS

DNS component in FreeIPA is optional and user may choose to manage all DNS records manually in other third party DNS server.

Please consider the following benefits of integrated DNS in FreeIPA before enrolling a custom DNS solution:

  • Clients can be configured to automatically run DNS updates (nsupdate) when their IP address changes and thus keeping its DNS record up-to-date. DNS zones can be configured to synchronize client's reverse (PTR) record along with the forward (A, AAAA) DNS record.
  • FreeIPA domain has automatically maintained LDAP and Kerberos SRV records allowing an easy autodiscovery in FreeIPA clients
  • FreeIPA domain has automatically maintained Microsoft Windows service records required for Trusts configuration.
  • Automatic management of ipa-ca.example.com DNS record keeping forward (A, AAAA) records to all FreeIPA servers with a Certificate Authority configured. This DNS record is used in all certificates issued by FreeIPA as a general point to obtain certificate validation either via OCSP responder or CRL.

Caveats

Caveats applicable to DNS apply as usual. It is extremely hard to change DNS domain in existing installations so it is better to think ahead.

Most importantly, do not shadow or hijack other DNS names! You should only use names which are delegated to you by the parent domain.

For example, if your company Example, Inc. bought domain example.com. you can use any domain in this sub-tree, e.g. whatever.example.com..

Not respecting this rule will cause problems sooner or later! (This caveat includes inventing your own top-level domain like int.)

  • Generally you will have problems with DNSSEC validation. This situation will be detected as domain hijacking.
  • Even without DNSSEC, you will have problems if the same name is used by multiple parties at the same time, especially when new top-level domains are delegated or during company mergers.

Internal-only domains

It is perfectly fine to configure certain DNS zones to respond only to clients in certain subnets or to apply other kinds of access control. For internal names you can use arbitrary sub-domain in a DNS sub-tree you own, e.g. int.example.com.. Always respect rules from the previous section.

DNS views / split-horizon DNS

General advice about DNS views is do not use them because views make DNS deployment harder to maintain and security benefits are questionable (when compared with ACL).

Problems:

  • Using one name for multiple different machines (e.g. public vs. internal) is confusing.
  • DNS caching on clients causes problems for machines roaming between different DNS views.
  • DNSSEC deployment is harder to maintain when views are involved.

Technically it is much cleaner to put all internal names in a sub-domain like int.example.com. (while example.com. is the public-facing domain) and restrict access to this sub-domain using ACL as described in the previous section.

Architecture

The DNS integration is based on the bind-dyndb-ldap project, which enhances BIND name server to be able to use FreeIPA server LDAP instance as a data backend (data are stored in cn=dns entry, using schema defined by bind-dyndb-ldap.

Security

FreeIPA LDAP directory information tree is by default accessible to any user in the network, or (if anonymous search is disabled) to any authenticated user. As DNS data are often considered as sensitive and as having access to cn=dns tree would be basically equal to being able to run zone transfer to all FreeIPA managed DNS zones, contents of this tree in LDAP are hidden by default.

Only the following users have read access to the DNS tree:

  • bind-dyndb-ldap service principal itself
  • Members of the admins group
  • Users with Read DNS Entries attributes
  • Users with per-zone permission have read access to the permitted zone (these permissions can be created with dnszone-add-permission command)

Debugging

When there is a suspicion that the DNS component is not behaving correctly, standard system log (/var/log/messages or system journal) can be consulted if there are any errors logged by BIND.

If the error is more subtle, BIND configuration (/etc/named.conf) can be updated to produce a more detailed log. Standard BIND documentation can be consulted for help.

Most common problems are caused by mis-configuration. Please see bind-dyndb-ldap documentation page and FreeIPA troubleshooting DNS page.

Bug reporting

Please follow instructions published by bind-dyndb-ldap project.

Additional Documentation