X-Trace

Basically, what is being proposed here is a system that will be present throughout all the different levels of any internet application so as to be able to help people debug problems that they encounter. The idea is that the internet is getting REALLY complex (which is very true - just look at how much material we have for this class), and therefore, we need some sort of tool that will help us debug problems.

X-Trace generally assumes that the flow of packets across the internet will generate a tree of causality. There's a very good example of this in the paper, with the root being a web browser, and the leaves being a tree of DNS requests, and a tree with an HTTP request that leads to an Apache call. X-Trace accomplishes this kind of tracing with some metadata that is kept by all levels of a request. The metadata includes a unique identifier, an operation identifier, a parent id, and some options. The unique identifier allows reports from the same request to be grouped together, whereas the parent id allows these reports to be arranged into the appropriate tree structure.

Thus, for an intermediate device, application, or library to implement X-Trace, it must essentially implement two different calls: PushNext() and PushDown(). PushNext() indicates that it is pushing the X-Trace metadata to the next logical node in the eventual X-Trace tree. PushDown() indicates that the metadata is being pushed to a lower layer.

Once everyone has implemented these calls, they can generate reports for each X-Trace request. These reports are sent to a local handler (for security purposes). The X-Trace metadata also has a tag that allows them to (optionally) send the report to the original requester. This step is optional, since a company like Wikipedia or Google may not want to reveal any information about their internal composition.

The major issue with X-Trace seems to be deployment. For some protocols, such as HTTP, deployment is made easy through the use of extension headers. For others, such as TCP, this becomes much more difficult, and requires some changes to the Linux kernel. For UDP, it is impossible without either changing the protocol itself, or adding a tiny layer on top of it. If X-Trace can be deployed across the internet, and protocols can be altered so as to support it, then it will be an invaluable debugging tool. However, the likelihood of such a deployment seems small.