AD Integrated DNS Zone restore/repair

With AD-integrated zones, there is no concept of "primary" or "secondary" zones; an integrated zone gets replicated to all DCs in the domain(*), and all of them are authoritative for it and can modify it, either by admin intervention or by dynamic updates from domain computers; whenever the zone gets modified, the AD replication process takes care of synchronizing the changes between all involved DCs.

This of course implies that all DCs which are also DNS servers get a SOA record for AD-integrated zones; and this is perfectly fine, as all of them actually are authoritative DNS servers for that zone.

And, indeed, it is considered best practice to use AD-integrated DNS zones, make all of your DCs (or most of them) DNS servers, replicate the zones to all of them and have all domain computers use two or more of them as their DNS servers. DNS is critical to proper AD operation, so that's a service you most definitely don't want to fail.

(*) This is the usual behaviour, but it can be changed depending on the zone replication scope.

OK, so, a quick rundown:

1. _msdcs is essentially where all those AD-critical SRV records are kept.
2. All your servers which need SRV records should be registering and refreshing them via dynamic DNS. You're (hopefully) not building your SRV records by hand.
3. The netlogon service performs DDNS refresh, with a according to this a default refresh frequency of 1 hour. But according to this, it refreshes every 24 hours - it's what I observe in the timestamps of my own SRV records as well.
   • Also be aware, DDNS updates have a dependency on the DHCP Client service, so don't disable the DHCP Client service even if your servers are statically addressed.
4. The default scavenging interval is 7 days. Scavenging removes any dynamic record whose timestamp is older than (todaysdate - scavengeinterval); those records would remain until deleted (either manually or by some other process like a DC demotion) if there were no scavenging. Scavenging does not touch static records (those you created by hand) unless you explicitly allow scavenging for the record.

So, keeping all this in mind, you should be fine with scavenging, as long as you are not scavenging more often than your records can refresh themselves. You can verify that your records really are refreshing themselves by taking a short look through the timestamps in whatever zone you are considering scavenging.

IMHO, scavenging is always a good idea, and yes this includes the _msdcs zone. If a DC stops refreshing its DNS records, scavenging will automatically remove those records and that's a good thing - you wouldn't want people resolving to broken DCs.

I consider the article Don't be afraid of DNS Scavenging. Just be patient. to be the canonical best practice for Windows DNS scavenging.