nat vm can browse but not ping, expected?

hi,

I just tried (first time) to set a vm (wheezy) virtual nic as nat: it works, it gets a 10.x.x.x adddress dynamically and can browse,
but ... can't ping anything, just localhost and gateway, 10.0.2.2.

is it expected?
and, where is it configured nat/dhcp in pve (2.1)?

Marco