Rewrite Rule and redirect to another port in Web Farm

Hi

I have 3 servers configured with IIS and named as DEMOCONTROLLER  , DEMOPRIMARY and DEMOSECONDARY.

My ASP.NET application is installed on default website on DEMOPRIMARY and DEMOSECONDARY server.

I can access the application using http://DEMOPRIMARY/TestApp  or http://DEMOSECONDARY/TestApp.

Even I can access it using http://DEMOCONTROLLER/TestApp which do the load balancing as expected.

My problem is when I host the application in another port, I am not able to access it.

For eq. I am able to access the application thro' http://DEMOPRIMARY:81 and http://DEMOSECONDARY:81 properly

but trying to access it using http://DEMOCONTROLLER:81 I am getting error "The connection has timed out".

Please help me to make this situation working ... 
             - what rule needs to be configured on global level ?  or how to do this redirect

-Rajesh