| dc.description.abstract | The number of hosts connecting to the Internet is growing day by day, and the available statistics show that this growth is exponential. This growth has made IP address a scarce resource. IPv6 is proposed as a long term solution to the problem of depletion of IP address space. IPv6 has many advantages over IPv4, and is carefully designed to serve the future requirements. But the migration from IPv4 to IPv6 can’t be done over night, because it requires extensive modifications to the existing infrastructure. It will take around 15 to 20 years to deploy IPv6 fully. Some temporary solutions to solve the problem have been proposed in the literature. One such temporary solution is NAT (Network Address Translator). Network Address Translator (NAT) gateway provides a way of utilizing the available IP addresses effectively. NAPT or Network Address Port Translator is one popular flavor of NAT gateway which uses one IP address and multiplexes many hosts to connect to the Internet.
On the Internet every connection is identified by four parameters. They are source IP address, source port number, destination IP address and destination port number. In each and every out-going packet the NAPT changes source IP address to its own IP address, but the source port is changed to a unique value that is used to associate incoming packets with the private network address. NAPT maintains full outbound connectivity and denies the internal hosts the ability to receive unsolicited inbound connections. That is, connection initiation can be done only from the internal host. The host outside the NAT can’t initiate a connection to the host behind the NAT. This denial of inbound connections is to provide security to the internal hosts. The NAPT is fully transparent to the end-users, since the source ports in the IP packet headers are translated on the fly.
In the normal client server architecture, the lack of inbound connectivity is fine because all servers are located in the public domain. But the current world is moving towards the peer to peer networking. In peer to peer networking, the distinction between a client and a server vanishes and, every host acts as both client and server. This is to exploit the databases distributed among the peers. Under these circumstances every host demands inbound connectivity. The major application of the peer to peer networking is in file sharing. This thesis proposes a novel technique to solve the problem of lack of inbound connectivity of NAT, by modifying the peer to peer file sharing protocol, while retaining the advantage of NAT in utilizing the IP address space effectively. In the proposed method all inbound IP packets are sent to the NAT gateway, and prior to that, NAT gateway is instructed, as to which private IP host these packets should go inside its own domain. For this to happen the initiator should know both the IP addresses of the NAT and the responder which is behind the NAT. This is done by modifying the directory service at the central host, which contains the details about the location of files. The modifications needed at the NAT gateway and to the peer to peer networking protocol to solve the lack of inbound connectivity problem of NAT, are presented in this thesis.
Organization of Thesis
The thesis is organized in 5 chapters as follows:
Chapter I gives an elaborate account of present status of the Internet. The problem of scarcity of IPv4 address space is discussed. The temporary and permanent solutions to solve this problem is discussed. The problem of lack of inbound connectivity of NAT, which gets more attention in peer to peer networking is stated. Here the scope of the work is defined.
Chapter II deals with a survey of the existing solutions to alleviate the lack of inbound connectivity problem of the NAT. The positive and negative aspects associated with each of these solutions are discussed.
Chapter III explains the proposed solution to solve the lack of inbound connectivity on the NAT.
Chapter IV deals with the implementation details of the proposed solution. Since the proposed solution is a protocol, all the packet formations used and all fields are explained in this chapter.
Chapter V summarizes the contributions made by the thesis. Suggestions for future work is also included in this chapter. | |
