Hi,
An exam is an exam which has its objects. From my personal experience with Juniper exams, 95% of t he questions/tasks are covered in the exam objects. But, there're corner cases, for example, a question that asks your knowlege for more than one specific technology, that may fall out of the exam objects.
To answer your question:
Of all the appendixes, of all student guides, the only one that is mentioned in the list of exam objectives is the appendix IS-IS of the routing study guide. Does this really mean that I can ignore all the appendixes with the exception of the one about IS-IS?
Yes. I only see ISIS is covered. Other technologies like ERP/RIP/IPv6 are either out dated or considered too difficult (will be covered in higher level certification)
For example: The list of exam objectives does not mention IPv6 (which is treated also in an appendix). I can ignore that too?
For this particular exam. You may ignore. But getting ready for next level certification, ipv6 is covered in various means, like BPG IPv6 NLRI, ospf3
By the way,
What about IPv4 calculation. I always use the free calculators you can find on the Internet. I did learn IPv4 (binary) calculation by hand, more than once but after some time its forgotten. May I expect questions that need binary IPv4 calculation by hand on the JNCIS-ENT certification exam?
I remember there's questions like this. They have a routing policy to export 172.29.0.0/16 orlonger. They will ask if some example prefixes are exported or not. This includes everything from 172.29.0.0/16-32 to 172.19.255.255/16-32
172.29.130.0/17 <<<Yes.
172.30.13.0/24 <<<No
Hope my information is what you are looking for