migrate AD data:

https://blogs.technet.microsoft.com/canitpro/2017/05/24/step-by-step-migrating-active-directory-fsmo-roles-from-windows-server-2012-r2-to-2016/

https://tekbloq.com/2017/05/15/decommission-uninstall-a-windows-2008-r2-domain-controller/

https://www.kieri.com/how-to-rename-windows-server-2016-domain-controller/#NETDOM

further issue:
https://support.microsoft.com/en-us/help/324801/how-to-view-and-transfer-fsmo-roles-in-windows-server-2003
https://community.spiceworks.com/topic/106110-demoting-a-domain-controller
https://www.petenetlive.com/KB/Article/0001453

seize PDC:
https://theitbros.com/transfer-fsmo-roles-from-failed-domain-controller/
https://www.quora.com/How-do-you-seize-a-FSMO-role-from-a-dead-domain-controller
if failed:
cmd->ldp.exe
cmd->AdsiEdit.msc

connection->bind-> auth user/pass domainname
view->tree-> cn=configuration,dc=vnakc,dc=com
dbl click CN=Sites,CN=configuration,dc=vnakc,dc=com
dbl click CN=VNA,CN=Sites,CN=Configuration,DC=vnakc,DC=com
Dbl click CN=Servers,CN=VNA,CN=Sites,CN=Configuration,DC=vnakc,DC=com
Found ISNTCASS - Rt Click -> Delete

error:
"The Specified Domain Either Does Not Exist or Could Not Be Contacted" on both DCs.
HKLM\CurrentControlSet\Services\Netlogon\Parameters\SysvolReady to state of 1



192.168.2.100	dc1
192.168.2.101	dc2
192.168.2.150	c1
192.168.2.151	c2

103.214.144.241