JNCIS-SP study guide has a chapter on layer 2 and layer 3 VPNs and I think that should be enough to understand the concepts. The book is very explanatory and presents the technology with relevant configuration knobs and examples.
Basically JNCIS-SP exam does not cantains labs or stimulator based question so you won't be asked to configure anything in exam, conceptual knowledge would be enough to pass the exam, but in real production environment you need to know the configuration part, so make hands on practice you can use VMX or Olive images in GNS3.
You do need to know how to configure and troubleshoot the topics in the exam. You won't be doing any configuration or simulations but they do ask mutiple choice questions that include needing the knowledge of the configuration commands, hierarchy and troubleshooting process.
You can take the sample exam here to get a feel for how these questions work.
It used to be very helpful, because sometimes you cover some topics and the exam does not cover, and that was pretty helpful. However, since of late, I have noticed that there a lot of questions on these exams that are not even convered in the courseware. Some you have to just know outright by expereince while others you sometimes can figure out with the aid of another related question or via process of elimination. The other thing I do, is also to look for key words in the courseware that is mentioned but not dealt with in depth, then search the website for information which you find in a lot of cases. Aso if any Appendix is attached, then they are source of test questions. The good thing is that you can mark a question for review and then go back. Exam tip, don't get worked by a question that beats you as you read it. If you dont know the answer by the time you finish reading the question carefully and completely and cannot figure it out in say 30 seconds, mark it and move on to the next. Answer the easiest questions first so you can lock up those points. Hope you pass!
[KUDOS PLEASE! If you think I earned it! If this solution worked for you please flag my post as an "Accepted Solution" so others can benefit..]
Remember that in the Juniper system you cannot skip levels but have to go from Associate > Specialist > Professional in order to get the certifications. One of the advantages of this consecutive approach is that they don't need to duplicate exam topic areas in upper level exams. Instead if a topic is deep enough they cover basics in lower exams and more detail in the higher one. And for many topics a single entry suffices for testing purposes.
Steve Puluka BSEET - Juniper Ambassador IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP) http://puluka.com/home