measr.net

 – measuring the Internet.


Network Architectures and Services
News (14.06.2012): new tests available (IPv6 tests)

Please install Java first: download


Today, most households use a Network Address Translator (NAT) to connect to the internet. NATs work against the IPv4-shortage problem in a way that they allow a private network to share one public IP-Address. The NAT then translates between the public and the private realm and creates a mapping for every outgoing connection. This works well as long as connections are established from the inside because the NAT is then aware of all incoming connections and can forward them to the appropriate private host. But as soon as a user wants to provide a service behind a NAT, the NAT is not able to map inbound packets to this host because no state exists for these packets. This problem is called the NAT/Firewall-Traversal Problem. There are already a large number of approaches to solve this problem. Unfortunately, none of them provides a general NAT-Traversal solution for legacy applications. One reason is, that the implementation of a NAT is not standardized. The behavior of NATs not only varies from vendor to vendor, but also from type to type. To evaluate and test as many NATs as possible, we created a little application that determines the properties of a NAT and makes some connectivity tests.