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The Annoying Subnetting Question–Think Big Bang Theory

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Yesterday on Day 1 of a 20411 Administering Windows Server 2012 class we had a question pop up on the DNS chapter.  Right off the bat I knew this question came for a brain dump web site.  Let’s just get my position out in public right off the bat.  I expect those who are going to take the exam to take the time to learn the technology.  If you do use a practice exam to prep, use it as a learning tool.  Do not just memorize the exam.  It will not do you or anybody else any good. 

From the perspective of others in the class, it was like watching the Big Bang Theory unfold in front of them.  We dove into this problem to try and find the correct answer the proper way using research.

Let’s first take a look at the question and then we will learn from it by finding the answers to all of the questions that do not have the answers for.

You work as an Administrator at iCompany.com. The iComapny.com network consists of a single domain named iComapny.com. All servers in the iComapny.com domain have Windows Server 2012 R2 installed. The iComapny.com network uses the network ID 192.168.1.0/26 and has a single DNS server named iCompany_DNS03.iCompany_DNS03 has a standard Primary DNS zone.

Which of the following options is the correct reverse lookup zone for the iComapny.com network?

A. 192.168.1-0.in.addr.arpa

B. 192.168.1.26.in-addr.arpa

C. 26.1.168.192.in-addr.arpa

D. 1.168.192-26.in-addr.arpa

E. 0.1.168.192.in-addr.arpa

Remember that I am not against the use of practice exams as long as you take the time to understand why an answer was right and why the other ones were wrong.

We eliminated the “noise” in this question an reworded it as follows.

You have an Network ID of 192.168.1.0/26.  What is the correct reverse lookup zone?

Much simpler.

We eliminated A and B because the syntax was just wrong. The IP address in a reverse lookup zone is written with its octets reversed. We then looked at the TechNet article Adding a Reverse Lookup Zone. On table 6.3 where we see that a subnetted reverse lookup zone is scoped using a Class B or Class C network. This allowed us to eliminate C. We then used the document RFC 2317: Classless IN-ADDR.ARPR Delegation to determine what would the proper syntax for a delegated classless reverse lookup zone would look like. This allowed us to eliminate D for two reasons. The first is that D is an attempt to perform this as a delegated reverse zone. There is nothing in the text of the problem for this type of a reverse lookup zone. Also, the syntax of D for a delegated reverse lookup zone was not correct to begin with. Look at the –26.  This was not correct. In conclusion, we went with E. for our answer.

Remember, memorizing a practice exam is not recommended. In the end, you still need to perform the job. If you do go that route, use it as a study guide, not a memorization tool. At 3 AM on a Sunday Morning after working all weekend with little to no sleep on a problem, the memorization of a test will not help you. Knowing the technology will. I know this from actual experience. Had I not taken the time to know my technology, I most likely would not have been successful when the heat was on.

References

RFC 2317: Classless IN-ADDR.ARPR Delegation

Adding a Reverse Lookup Zone

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