Master Server IP problem

I still get the feeling that you have not gone through the TNs that I have posted yesterday....

Don't replace the hosts entries - add them to /etc/hosts. Exactly as per your opening post.

Because NBU was installed with the names on the .9 subnet, you cannot remove these hosts entries or bp.conf entries. NBU will stop working. Especially on the master server.

You will see in TECH54733 that the original master server name is still the 1st entry in bp.conf and that the name on the 2nd network is added as additional SERVER entry. 

The clients only need to know about the 'b' names and IP addresses for the master and media servers in their hosts files and only 'b' names in bp.conf for SERVER entries. 
Change their CLIENT_NAME entries to the 'b' network names.
 

Please draw your network picture as in TECH54733, fill in your hostnames and then add hosts entries.
Test network comms at OS level with commands like ping and traceroute between servers and clients.

If OS comms is fine, add bp.conf entries. 
Restart NBU on Master server after additions to bp.conf.

Test NBU comms with bpclntcmd commands.
Clear NBU host cache if bpclntcmd commands do not give expected output. (see TNs above...)