At a time only one master can backup the client.

At different times it is possible (A backs up the C client on Monday , and B backs up the C Client on Tuesday)

Officially it is not supported, but it can be tweaked to work .  Browsing for images in the BAR GUI is a different story  ;)

On the Client only:

Windows Client : You can change this registry key to point the SERVER = <Master Server >

HKEY_LOCAL_MACHINE\SOFTWARE\VERITAS\NetBackup\CurrentVersion\Config\
SERVER = Master Server name

Unix Client

/usr/openv/netbackup/bp.conf
SERVER  = Master Server name

I am backing up my own laptop to two different masters. Only one can be the Master, but the other one is simply listed as another Server. When I want to test user-initiated backups and restores to/from my lab environment, I simply add -M <lab-master> to the command line. Scheduled backups from my lab master also work 100%, no configuration change needed.
I do not recommend trying to do backups simultaneously, especially if client C is a Windows system and need to take snapshots for open file backups.
If you have any database agents, it will ONLY be sent to the Master (1st server entry).

If you do incremental from two master servers you mess up the archive bit logic and end up with "unique" file on both master servers.

Can't really recommend to have a client backup from two master servers. If you want to have redundant backup data, duplicate on the master server or use the inline copy feature.

Thanks You all for replay. now i understand concept.thanks alot.