[snmp] Auto-discovery

[tausif]

I am trying to make application which automatically should discover all the devices in the LAN. I need to discover the devices based on 

1. range of IPs
2. Subnet Mask
3 Default gateway.

is there any way of doing the auto-discovery using westhak APIs? is there any sample example for the same?
if not, is there any way of doing it? Actually i m kind of avoid doing PING first and then send SNMP request.
There must be some other way right? 

Can I make use of DatagramPacket / DatagramSocket? if any one having sample code will be a great help

thanks