Skip to main content

The Annoying Subnetting Question–Think Big Bang Theory

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

Comments

Popular posts from this blog

How to list all the AD LDS instances on a server

AD LDS allows you to provide directory services to applications that are free of the confines of Active Directory.  To list all the AD LDS instances on a server, follow this procedure: Log into the server in question Open a command prompt. Type dsdbutil and press Enter Type List Instances and press Enter . You will receive a list of the instance name, both the LDAP and SSL port numbers, the location of the database, and its status.

How to run GPResult on a remote client with PowerShell

In the past, to run the GPResult command, you would need to either physically visit this client, have the user do it, or use and RDP connection.  In all cases, this will disrupt the user.  First, you need PowerShell remoting enabled on the target machine.  You can do this via Group Policy . Open PowerShell and type this command. Invoke-Command –ScriptBlock {GPResult /r} –ComputerName <ComputerName> Replace <ComputerName> with the name of the target.  Remember, the target needs to be online and accessible to you.

Error icon when creating a GPO Preference drive map

You may not have an error at all.  Take a look at the drive mapping below. The red triangle is what threw us off.  It is not an error.  It is simply a color representation of the Replace option of the Action field in the properties of the drive mappings. Create action This give you a green triangle. The Create action creates a new mapped drive for users. Replace Action The Replace action gives you a red triangle.  This action will delete and recreate mapped drives for users. The net result of the Replace action is to overwrite all existing settings associated with the mapped drive. If the drive mapping does not exist, then the Replace action creates a new drive mapping. Update Action The Update action will have a yellow triangle. Update will modify settings of an existing mapped drive for users. This action differs from Replace in that it only updates settings defined within the preference item. All other settings remain as configured on the mapped drive. If the