In today’s Internet we see an increasing deployment of middleboxes. While middleboxes provide in-network functionality that is necessary to keep networks manageable and economically viable, any packet mangling — whether essential for the needed functionality or accidental as an unwanted side effect — makes it more and more difficult to deploy new protocols or extensions of existing protocols.
For the evolution of the protocol stack, it is important to know which network impairments exist and potentially need to be worked around. While classical network measurement tools are often focused on absolute performance values, PATHspider performs A/B testing between two different protocols or different protocol extensions to perform controlled experiments of protocol-dependent connectivity problems as well as differential treatment.
PATHspider now contains 3 built-in plugins for measuring path transparency to explicit congestion notification, DiffServ code points and TCP Fast Open. It’s easy to write your own plugins, and if they’re good enough, they may be included in the PATHspider distribution at the next feature release.
We have a GitHub repository you can fork that has a premade directory structure for new plugins. You’ll need to implement logic for performing the two connections, for the A and the B tests. Once you’ve verified your connection logic is working with Wireshark, you can move on to writing Observer functions to analyse the connections made in real time as PATHspider runs. The final step is to merge the results of the connection logic (e.g. did the operating system report a timeout?) with the results of your observer functions (e.g. was ECN successfully negotiated?) and write out the final result.
We have dedicated a section of the manual to the development of plugins and we really see plugins as first-class citizens in the PATHspider ecosystem. While future releases of PATHspider may contain new plugins, we’re also making it easier to write plugins by providing reusable library functions such as the tcp_connect() function of the SynchronisedSpider that allows for easy A/B testing of TCP connections with any globally configured state set. We also provide reusable observer functions for simple tasks such as determining if a 3-way handshake completed or if there was an ICMP unreachable message received.
Visit the PATHspider website to learn more.