public class ClassName {
    private static string ipAddress;
       static {
        ipAddress = ApexPages.currentPage().getHeaders().get('X-Salesforce-SIP');
        }

      @RemoteAction
      public static String userDetails() {
        showIpAddress();
       }

      public static void showIpAddress(){
       system.debug('ipAddress ' + ipAddress );
       }
    }