Hi,
I have a forest with a single domain/site W2008R2 functional level. The first DC was built without an issue. I have recently added a second domain controller to the domain, and this has caused the first to fail (although the second seems to be filling the gap for the moment).
The second domain controller was added using dcpromo, using the option to add a domain controller to an existing domain. Both the DNS and Global Catalog roles were added. The replication appeared to succeed without any issues.
The other bit of information that may be useful, is that dcpromo did say that it was unable to find any DNS servers authorititative for the domain when adding the second DC. I checked dcpromoui.log, and it seemed to have queried the SOA record correctly, so wasn't sure what was causing the warning. In any case, the DNS replication between the two was successful.
The initial symptom I've noticed is that the first domain controller's LAN interface has switched from the "Domain" profile, to the "Private" profile. For some reason it no longer thinks that interface is connected to the domain.
DNS servers on dc01 is set to 127.0.0.1 / Blank
DNS servers on dc02 is set to dc01 IP / 127.0.0.1
I'm currently doing further investigation, so will post information as I find it. Any help greatly appreciated.