The technique has been criticised because it imposes certain limits on users by virtue of the fact that their broadband connection no longer has the use of a fixed unique IP address, but is rather sharing an address with other users – in BT’s trial, up to nine other users. This means, for instance, that users can’t serve content to the wider Internet from servers on their home network; and BT admits that it can also affect activities such as online gaming and dynamic DNS services.

via BT Retail Tests Controversial Carrier Grade NAT IP Address Sharing.