bandwidth utilization problem.how to identify the hacker?

[m_aurangzeb]

I am working in a ISP.I have observed that the bandwidth utilization of our ISP is more than that it should be. coz at late night when users online are minimum at that time it shows me maximum bandwidth utilization on MRTG graph. how can i identify that which IP is utilizing my resourses(bandwidth). is there any software which can identify this? or is this possible its solution is possible by doing specific configuration on router or cisco access server 5300 or pix firewall. if yes then pls tell me just the command.

[pradeepde]

You can enable the "ip accounting" command on the interface and find out which IP is pumping more traffic. The ip accounting command records the number of bytes (IP header and data) and packets switched through the system on a source and destination IP address basis. Only transit IP traffic is measured and only on an outbound basis; traffic generated by the router access server or terminating in this device is not included in the accounting statistics. For more information on this command have a look at the following URL.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cr/hiap_r/apl_i1h.htm#wp1201321