Using SNMP to query a vCenter 5.5 server from an Ubuntu server

I need to query a vCenter 5.5 server member of a vSphere 5.5 infrastructure via SNMP from an Ubuntu server on the same LAN.

I enabled Reciever 2 for the IP of the vCenter server for port 162 and community "public" but I from the Ubunti server I am unable to get any information from the vCente server.

I simply get no answer while the Ubuntu server can query other servers in the same LAN with non problem.

What else should I do on the vCenter server?

Whare can I locate any sample of correct syntax commands to query the vCenter server via SNMP from the Ubuntu server?

Regards

marius