Syakshanulla,
The only time you really need to specify the port under the serverfarm/rserver is if the port the client hits the vip on is different from what the application on the server is using.
For example if the class-map was for udp port 53, but the server was listening on port 54 you would need to specify the port number.
If for example your class-map was like this
class-map match-any vips
match virtual address 1.1.1.1 udp any
Since this vip is listening for any udp port you would not want to use the port under serverfarm/rserver. Whatever destination port the client sends to the vip by default will be passed on to the backend server. Putting the port on the rserver forces the ACE to change the destination port to whatever you specify.
Hope this helps.
Regards
Jim
