Hi Gopinath,
The best option here is to use the Security Audit Log (SM19/SM20) to determine which ip adress is accessing your system.
By default the terminal name is logged, not the IP address of the computer, thus the SAP Note below must be followed in order to record the IP address instead of the terminal name:
1497445 - SAL| Logging the IP address instead of the terminal name
After this configuration is made you will be able to check which is the IP address that each user is using to access your system.
Cheers,
Filipe Santos