Machines inside of your network can be partially concealed through IP masquerading (the version of Network Address Translation most used in Linux).

CNN: Analysis: Linux security

There are a variety of problems associated with masking IPv4 address space behind network address translation technologies, especially Large Scale NAT (LSN) or Carrier Grade NAT (CGN).

FORBES: IPv6: The Time To Consider Making The Switch Is Now

However, ISPs have so widely deployed network address translation (NAT) devices, which coordinate multiple intranet addresses through a single Internet address, that they're in no hurry to move to IPv6.

CNN: New protocol sneaks IPv6 traffic over the 'Net