Patch 1: Right now, we have SELinux procesing split between the provider
and responder. This patch moves it to provider only. So no partial
results are sent to responder for further processing, which makes the
processing steps easier to follow. (Originally the idea was to move the
processing to the responder, but completely removing the procesing from
provider and let it just update db turned to be more invasive than
completely removing the procesing from responder.) If this patch is
accepted, SELinux policy needs to be modified to allow sssd_be to write
the selinux login files.
Patch 2, 3: Reuse cached selinux maps. Patch 2 shows how it is done with
refresh interval fixed to 120 seconds. Patch 3 adds ipa option to
configure this interval (I didn't want to merge these patches for better
readability). Default value is 30 seconds.
Patches are attached.
This patch removes yet another set of custom and parallel error codes
specified in the sdap_result enumeration, and instead uses the new
unified error codes.
This is to be applied on top of the previous patchset that adds SSSD
specific error codes.
I have done minimal testing with my IPA install and it seems to work
fine as far as ldap+SASL/GSSAPI auth goes.
Simo Sorce * Red Hat, Inc * New York
I have created a design page to discuss DNS updates of Active Directory
For your convenience, the wiki page is also copied below. Comments and
feedback are appreciated.
== Active Directory client DNS updates ==
* [https://fedorahosted.org/sssd/ticket/1504 RFE AD dyndns updates]
=== Problem Statement ===
Clients enrolled to an Active Directory domain may be allowed to update
their DNS records stored in AD dynamically. At the same time, Active
Directory servers support DNS aging and scavenging, which means that stale
DNS records might be removed from AD after a period of inactivity.
While DNS scavenging is not enabled on Active Directory servers by default,
the SSSD should support this use case and refresh its DNS records to
simulate the behavior of Windows AD clients and keep their address records
from being removed if scavenging is used. The SSSD should also enable the
clients to update their DNS records if their IP address changes.
=== Overview of Windows client side DNS updates ===
This section provides a brief overview of how Windows clients may update
their DNS records and how scavenging is configured and performed in a
Windows domain. For more complete information, please follow the links at
the bottom of this page.
==== Windows Resource Record information ====
To be able to detect if the resource record is stale, every dynamically
created RR in the Windows DNS has a timestamp that is updated with the
dynamic update if scavenging is enabled. Manually created DNS records do
not have a timestamp. In order to update the timestamp, the DNS records
are refreshed periodically even if they actually haven't changed, just to
bump the timestamp.
A special timestamp value of 0 can be set to the resource record, indicating
unlimited lifetime of the record. Such record is never scavenged.
==== Update and refresh ====
When a Windows client updates its DNS information, it may perform either an update or a refresh.
* an ''update'' is performed when the IP address of a client
changes. Involves a refresh and a change of the IP address(es).
* a ''refresh'' does not change the IP addresses themselves, but rather
only updates the timestamp of existing resource record, keeping it
from being scavenged.
In order to maintain a heartbeat on the resource records, the Windows
clients perform updates and/or refreshes under conditions outlined in the
==== Scavenging timeouts ====
In the zone properties, there are two timeout settings that are affecting the scavenging
* No-refresh interval - minimal interval between last refresh after which
the record can be refreshed again
* Refresh interval - interval during which the refreshes are allowed. After
the refresh interval passes, the stale records can be scavenged. In other
words, the refresh interval starts at `timestamp + no_refresh_interval`.
==== Windows clients update and refresh intervals ====
For Windows clients, refreshes or updates generally occur for the following
* the computer is restarted
* the DHCP lease is renewed
* periodicaly every 24 hours by default
* this is configurable in the windows registry using
the `DefaultRegistrationRefreshInterval` key under the
The SSSD updates should be modeled to be close to what the Windows clients do.
==== SSSD clients refresh intervals ====
The SSSD would perform the dynamic DNS update or refresh under the following
* the back end becomes online
* this would also cover the case where computer is restarted. For
long-running deployments where the SSSD is almost never offline, the
back end would only ever become online after bootup
* periodically based on a configuration option
* the configuration option could be named `ad_dyndns_refresh_interval`
or similar and it would default to 24 hours
* the granularity will be hours. AD interface also allows to set the
refresh and no-refresh interval in hours, too, so our granularity should
not be lower. Seconds, on the other hand, seems too granular.
* admin could change the option to be same as DHCP lease for example to
simulate the case where Windows workstations refresh the address after
lease is renewed
=== Overview of the solution ===
Because the DNS records scavenging is not on by default on the server
side, the client side DNS updates would be off by default as well. A new
configuration option, called `ad_dyndns_update` (bool) would control
whether the DNS update should be performed.
==== Addresses used during the update ====
We will reuse a similar mechanism used in the IPA provider where the
address used to connect to the AD server LDAP connection is used by
default. Optionally, for machines that use IP aliasing or setups that wish
to update both IPv4 and IPv6 addresses of an interface at the same time
there will be an option `ad_dyndns_iface`.
Contrary to IPA dynamic DNS update that generates the PTR record in the
bind dyndb plugin, AD wouldn't update the PTR record on its own when only
A/AAAA record is updated. To be able to keep the forward and reverse zones
in sync, the AD dynamic update message would also include updating the
PTR records. PTR records update would not be on by default and could be
turned on by setting an option (perhaps `ad_dyndns_update_ptr`) to true.
==== Future and optional enhancements ====
* Currently the information on whether scavenging is enabled and how
often is it performed is stored in GPOs. When SSSD has the ability to
process Group Policies, we would add a new special value to the
periodical update option that would tell the SSSD to simply honour the
* We could also integrate with netlink to perform IP address refresh on DHCP lease renewals. This could be filed as a separate ticket and implemented later.
=== Implementation details ===
For the update itself, we can simply use the nsupdate utility the way we
use it in IPA domain. The update code is already there, it is mostly a
matter of splitting the code to be IPA-agnostic.
One change compared to the IPA code would be that IPA only sends the refresh
when the addresses change, to avoid unnecessary zone transfers on the IPA
server. As stated above Windows clients typically refresh their address
even if nothing changed, so our update code would run unconditionally,
too, based on timed events.
1. The use of `resolv_init` in the dynamic DNS update code should be
inspected. If it is not needed anymore and the resolver code could
already be told per-request to only go to DNS and ignore `/etc/hosts`,
the initialization should be removed.
1. A new module shared between IPA and AD providers shall be created. This
module will contain generic functions related to dynamic DNS update such as:
* a variant of `ipa_dyndns_add_ldap_iface` decoupled from IPA dependencies
* function to gather all addresses of an interface
* utility functions
1. The existing `fork_nsupdate_send` request would be split out to a generic
request that calls nsupdate with a specified message. This request would be
placed in the module created in the previous step. The IPA provider would
be converted to use these new generic request. The interface might look like:
struct tevent_req *be_nsupdate_send(struct tevent_context *ev, const char *nsupdate_msg);
errno_t be_nsupdate_recv(struct tevent_req *req, int *child_retval);
1. In the AD provider, a variant of IPA dyndns code would be created,
using AD specific data structures and options. This interface would
consist of a tevent request that would wrap `fork_nsupdate_send` using
`struct ad_options` and an initializer function called on provider startup.
1. If the `ad_dyndns_update` option was set to `true`, then the AD provider would:
* set up a periodic task running each `ad_dyndns_refresh_interval` hours
updating the DNS records
* set up an online callback to run the DNS update when the back end
=== List of all new configuration options ===
1. `ad_dynds_update` `(bool)` -- whether to perform the dynamic DNS
update. Defaults to false.
1. `ad_dyndns_refresh_interval` `(integer)` - how often to run the periodic
task to refresh the resource record
1. `ad_dyndns_iface` `(string)` - instead of updating the DNS with the
address used to connect to LDAP, which is the default, use all addresses
configured on a particular interface
1. `ad_dyndns_update_ptr` `(bool)` - whether to also update the reverse
zone when updating the forward zone
=== How to test ===
1. Test that forward and reverse zone updates work
* Make sure DNS updates are enabled on the zone
* Right-click the zone and select the "General" tab
* There is a combo-box labeled "Dynamic updates". Toggle it to "Secure only".
* Click "Apply"
* Prepare a client with dynamically updated DNS address
* the easiest way is to join the client with realmd - `realm join
* Test updates when the address has changed
* Change the address of a client
* Perform an action that would trigger an online callback such as login
* In the AD MMC check if the DNS address is the same as the new address
on the client
* Depending on the settings of `ad_dyndns_iface` or `ad_dyndns_update_ptr`
also check if all expected addresses have been updated in both forward
and reverse zones.
* Test periodic refresh
* Set the periodic refresh (`ad_dyndns_refresh_interval` in this document)
to some low value
* Wait until that value passes or modify the system time
* The timestamp of the resource records would be changed after SSSD ran
its periodic task
1. Test DNS scavenging
* Enroll two SSSD clients into AD
* Turn one of them off after enrollment. This client will be scavenged.
* Let the other one up and set its `ad_dyndns_refresh_interval` to a
value shorter than the scavenging interval
* Enable DNS scavenging on the server
* In the DNS MMC console, right-click the DNS server in the tree view,
select Properties and navigate to the "Advanced" tab
* Enable the "Enable automatic scavenging of stale records" toggle and
select a meaningful period
* Hit apply
* Enable DNS scavenging for the zone
* Open the DNS administrative console
* Right-click the zone and select the "General" tab.
* Click the "Aging" button
* Enable the "Scavenge stale resource records" toggle
* Set the no refresh and refresh interval to a low value.
* Check the "This zone can be scavenged after" text box. It should list
a date and time shortly in the future.
* Let the scavenging interval pass
* The client that was turned off after enrollment should be scavenged. You
should no longer be able to see its records in the DNS zones on the server.
* The other client's DNS records should remain intact in the DNS MMC console
=== Links and recources ===
* [http://technet.microsoft.com/en-us/library/cc759204%28v=ws.10%29.aspx Understanding aging and scavenging]
* [http://technet.microsoft.com/en-us/library/cc757041%28v=ws.10%29.aspx Using DNS Aging and Scavenging]
* [http://blogs.technet.com/b/networking/archive/2008/03/19/don-t-be-afraid-... Don't be afraid of DNS Scavenging. Just be patient. by MSFT Networking Team]
=== Author(s) ===
* Jakub Hrozek <jhrozek(a)redhat.com>