This is a question for slightly older Member Exclusive Content > Enforcing Security Based on Identities: Slides, Video, and Q&A presentation. Unfortunately, the comment section there is closed, so I'm asking a question here, please see the question below:
The presenter @Peter_Elmer and the host @PhoneBoy repeated that all the Domain Controllers (DCs) would replicate the User login events almost instantly. And this is the reason there will be duplicate information on the Identity Collectors... Is it really the case? Hope the answer will help to other admins as well.
It is stated twice during this great recorded session, first in minute 38 "Identity Sources: Identity Collector
Design guidelines and options" (page 34) and then presenter returns back to the same page on minute 55 during QnA to state:
All Logon Servers inside a ‘fully trusted’ domain are sharing login events
I lived up to this day thinking that Domain Controllers only synchronise Active Directory DB (e.g. users, passwords and GPO mostly). And Event Log (for the DC events such as login/logoff) is sitting locally on the DC server only. This is the reason all security monitoring tools for AD need to be installed on each DC. That is one can read the config from _any_ DC. But Security events are always _local_. Was I totally wrong?
#Potential explanation of DPD seeing event twice (even without DC replicating Audit Events):
I can see a change to cause a clash if ALL collectors monitor ALL DCs and then report to ALL PDPs. That is IdentityCollectoer1 and IdentityCollector2 each monitoring DC1 DC2 DC3 and DC4.
I also found something like "by default, security events are local" - this implies there is some non-default settings in AD. But I was not able to find anything related to such config.
One of many pages dated to 2005 (I hope not much changed in AD since then) https://techgenix.com/ACommonMisconceptionRegardingSecurityLogs/
Domain controllers host Active Directory, which manages the security of your Windows-based networks. If you have several domain controllers in the same domain, Active Directory information is automatically replicated between them so that they all contain identical (except for replication delay) copies of Active Directory and therefore contain identical security information. But do they also contain identical copies of the Security log?
No. That’s a common misconception. Security logs are not replicated between domain controllers. To see why, remember that a user is always authenticated by some specific domain controller in a given situation, so if logon/logoff auditing is enabled on all domain controllers, a logon security event will only be logged to the actual domain controller that handles the authentication of the user.
So don’t assume AD replication means Security log replication!
Events we are discussing
Event ID Description
|4624||An account was successfully logged on|
|4634||An account was logged off|
Finally, the KB recommends totally different approach to what is recommended by Peter Elmer:
Identity Collector - Technical Overview - sk108235 Identity Collector Redundancy section:
Identity Collector currently does not offer an "out of the box" redundancy. However, the following configuration can offer this feature:
Install Identity Collector on two separate Windows server machines.
Configure both for query the same identity servers and gateways (all configuration is identical).
With this configuration, you will have "Active/Active" redundancy.
The domain controllers should not be dramatically affected by this change, as the API Identity Collector is using is light resource consumer. On the gateway side, only the first event will be processed (the second one will be ignored).
P.S. Finally, I'm aware that users are usually silently disconnecting from the network and no log-off events are available.