Why cannot NAT be adopted on a permanent basis?
Many applications, especially emerging peer-to-peer applications, cannot operate correctly using NAT. This implies that many applications cannot be used if NAT is being deployed in a network. The following is a list of such applications: • Multimedia applications, including videoconference applications, voice over IP and video on demand, cannot be utilised on NAT enabled devices. The protocols used for such applications, namely, RTC and RTCP (Real-time Transport Protocol and Real Time Control Protocol respectively) use UDP with dynamic allocation of ports. NAT does not provide support for the latter. • Kerberos authentication requires the source address. NAT devices modify the source address, this address being present in the IP header and therefore, this type of authentication is not possible. • IPSec allows data authentication, integrity and confidentiality. However, since NAT modifies the address in the IP header, IPsec loses its integrity when NAT is used.
