一動態網路位址轉換之方法以溝通位於私有網路中之機器

Abstract

NAT是一個被廣泛應用於解決IPv4中IP位址不足問題的方法。透過NAT，我們便能利用私有的IP位址以節省IPv4之位址空間。然而，傳統的NAT只支援往外部的連線。也就是說，在公用網路中之機器並不能建立往內部之連線。因此，公用網路中之機器並不能和私有網路中之機器溝通，除非已有相關的固定設定或往相關的外部之連線。 關於上述之問題目前雖已有數個解決方法被提出，但所有的方法都有一些缺點或副作用。因此，在本論文中我們提出了一個稱為DCNAT的方法來解決此問題。此方法利用了一個稱為NAT Agent的外加模組，使得往內部之連線能夠利用一個註冊的程序而動態建立。換句話說，在公用網路中之機器在和NAT Agent註冊之後，將能和私有網路中之機器溝通。 DCNAT能夠更進一步的應用到群播服務的環境中。。透過一個支援群播服務之DCNAT (MDCNAT)，網際網路中之服務提供者(ICP)可以利用一個proxy來將一份資料送至許多機器。此proxy會替ICP向支援MDCNAT之NAT 路由器註冊訂閱者之資訊，並將群播之資料送至這些路由器。在收到資料之後，各路由器上之Multicast Agent將會利用一轉送機制或一子網路群播機制將此資料送至位於私有網路中之訂閱者。

NAT is a widely deployed solution to IP address depletion problem in IPv4. With NAT, we can use private IP addresses to save the IPv4 address space. However, traditional NAT would only allow outbound sessions (from a private network to the public network), i.e. a host in the public network can’t establish an inbound session toward a private network. Therefore, a host in the public network can’t communicate with a host in a private network except that the latter has a static address binding or has established an outbound session with the former. There have been several solutions to the above problem, but all of them suffer from some drawbacks or side effects. Therefore, in this thesis we present an approach named Dynamic-configurable NAT (DCNAT) to resolving the inbound session problem. In the approach, with an add-on NAT Agent on the NAT router, an inbound session can be dynamically configured through a registration procedure. That is, hosts in the public network (e.g. the Internet) can communicate with hosts within a private network after registering an inbound session with the NAT Agent. The presented DCNAT can be further enhanced to support applications with multicast data delivery. With the multicast-capable DCNAT (MDCNAT), an ICP (Internet Content Provider) can simply provide the subscription information of the subscribers and a copy of data to an MDCNAT proxy. The proxy can register, on behalf of all subscribers, with all MDCNAT-enabled NAT routers, and then sends a copy of data to each MDCNAT-enabled NAT routers involved. On receiving the data, a Multicast Agent in each designated NAT router will send the data to the subscribers within the private network via a multiple-unicast forwarding procedure or a subnet multicast.