The 192.168.22.0 address space is indeed designated a private address space, but that does not mean that convad could not use them on their own equipment. Just means that other ISPs will not route the traffic beyond Convad. This will not interfere with your client even if you did use this address space as your client would never use this address to talk to anything past their own internal network and it will not be shared with your client via any networking protocol. You will be NATing the address to a public address to anything on the internet. If you are concerned you can block at the boarder router all private addresses.