[Serusers] multiple SER with 1 mysql server

Hi. I have a centralized mysql server for SER database, and have 2 SER server connecting to the database. I failed to bridge UA 1 that is connected to SER A and the other UA 2 that is connected to SER B. Quite confused with the domain and alias actually, I wish to differentiate UA that register to different SER, thus I configure such that SER A has its IP as domain name and SER B has its IP as its domain name. Is it inappropriate to do that? What is the proper way to do so? Any guideline that I can bridge UA that is connected to different proxy to talk to each other? Thanks in advance. =) Regards, Chia