IP architecture considerations are at the core of the issues facing IPv4 today.9 In architecture terminology, IPv4 has lost transparency, defined as:
the original Internet concept of a single universal logical addressing scheme, and the mechanisms by which packets may flow from source to destination essentially unaltered.
Transparency is related to the existence of the end-to-end principle, at the core of the design of IPv4 and the Internet. This end-to-end principle may be summarized as [RFC2775]:
- Certain functions can only be accomplished by the end nodes. For example, failures in transmission and end-to-end security can only be managed by the end nodes. As such, state of the end-to-end communication must only be kept by end nodes and not by the network. The network is enabled to re-route packets transparently and efficiently, since no state is kept in the network.
- Transport protocols are designed to provide the required functions over a non-guaranteed IP network. Enhancements [RFC2581] were also integrated in end-nodes to better manage congestion.
- Packets can flow unaltered throughout the network and IP addresses are used as unique labels for end systems.
Implications of NAT in the network are illustrated by the following issues [RFC2993]:
- NAT is a single point of failure. Since a NAT keeps state, any failure of the NAT requires that all the current connections of all nodes behind the NAT be re-established.
- Application-level gateways(ALG) ...