This happens only in complex environments . I’ve loads of remote DPs in untrusted forests. One of the remote DP installation was not going very well. DP was not getting installed at all. Checked and confirmed all the requirements like a) Require the Site server to Initiate Connection to this Site System b) Use another account for installing this site system (this account must have local admin rights on remote DP).
Following are the errors in distmgr.log :-
Upgrading DP with ID 33554439. Thread 0×2490. Used 1 threads out of 5.
CWmi::Connect() failed to connect to \\["Display=\\RemoteDP.com\"]MSWNET:["SMS_SITE=RSP"]\\RemoteDP.com\\root\CIMv2. Error = 0x800706BA
DPConnection::ConnectWMI() – Failed to connect to RemoteDP.com.
Failed to install DP files on the remote DP. Error code = 1722
The error 0x800706BA translates to “The RPC Server is unavailable”. I tried remote WMI tests using wmimgmt.msc and wbemtest with no luck. Telnet was not working for remote DP ip for the port 135 from the primary server. The port 135 is used for RPC services. The cause to this problem was very simple. The RPC port 135 was not opened between primary server and remote DP in untrusted forest. We opened the port 135 and remote DP got installed successfully.