+ Connect network where address space in one network overlaps, partially or fully, with that of another
+ twice NAT helps network already connected to internet with a routable public address space to switch to another address space without requiring address renumbering
+ describe in RFC2663, August 1999
- available in current products (e.g. CISCO and juniper routers)
+ with twice NAT external clients can initiate communication with internal server (unlike traditional NATs)
Purpose of twice NAT is quite different than standard NAT