From in the VE context, you cannot manage ip addressing at all. Any attempts via config files or ifconfig will be futile. Instead, you should use "vzctl set VEID --ipadd x.x.x.x --save" from the HN as already explained and documented in the manual. So, just to be clear, you do not need to / cannot use debians interface management scripts/configs from inside the VE. The VE ifconfig output you provided shows that the address was added correctly to your VE. Assuming your HN can route that address properly, your VE will have network connectivity.