When creating a new LXC Centos 7 container in Proxmox 4.x and I select use host DNS settings it uses an IP in 10.0.0.0/8 range, forget exactly what IP, rather then host DNS server.
# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
libpve-common-perl proxmox-ve
0 upgraded, 0 newly installed, 0 to remove and 2 not upgraded.