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I have two sets of site links for each of my Active Directory sites - one set to HQ, one set to DR. Links to HQ are 100 cost. Links to DR are 200 cost. The KCC (obviously) generates connections over the 100 cost site links. We're going to take all of HQ offline next month for power maintenance, which should cause the KCCs for the remote sites to replace the existing replication objects to HQ with ones to DR over the 200 cost links.

When we bring HQ back up, will the KCCs at the remote sites replace the replication objects to the DR site with ones to HQ automatically? My gut says "of course it works that way!", but some Microsoft documentation says:

There are two phases of topology generation. During phase one, the KCC evaluates the current topology, determines whether replication failures have occurred with the existing connections, and constructs whatever new connection objects are required to complete the replication topology. During phase two, the KCC implements, or "translates," the decisions that were made in phase one into agreements between the replication partners.

This makes it sound like the KCC will only recalculate the replication topology in the event of a replication failure.


p.s. if you tell me to repadmin /kcc in a loop, I'll karate chop you in the throat.

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  • If you don't like repadmin /kcc loops, how about repadmin /kcc inside a do-while? =D – HopelessN00b Dec 21 '12 at 19:54
  • Same thing – MDMarra Dec 21 '12 at 19:56
  • @MDMarra: That looks terribly painful. – Scott Pack Dec 21 '12 at 20:01
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The KCC will fail back automatically. It runs every 15 minutes as you know, and it performs "both phase 1 and phase 2" to use your example above, as part of its logic on each run.

Essentially, the KCC will keep trying the "failed" DC indefinitely, just in case it comes back. When it does come back, you'll see this event in your log:

Event 1129

Source: ActiveDirectory_DomainService

To improve the replication load of Active Directory Domain Services, a replication connection from the following source directory service to the local directory service was deleted.

[The failover connections that were automatically created when your main DC failed will be here.]

Here's a good MS blog post with a lot more detail. It's a 3 parter, very detailed, I linked part 3 that mentions fail back: http://blogs.technet.com/b/isrpfeplat/archive/2011/12/11/disaster-recovery-site-and-active-directory-part-3-of-3.aspx

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