9 Replies Latest reply: Nov 6, 2013 11:39 PM by ciscoprof RSS

    Private versus reserved IP addresses


      Here is an example of the kind of treacherous nuance in which the 153 practice questions that come with Odom's ICND1 book (and are served through the Boson exam engine) seem to delight.


      I am a CCENT candidate, have not yet taken my test, and have developed pretty solid confidence with the Boson ExSim Max exams. But whenever I feel that I need a dose of humility and reaffirm my fear that I will not have enough time to answer all of the questions in the real exam, I revisit the Cisco Press questions.


      Many of these questions blend multiple distinct topics really make it impossible to succeed by guessing or luck. That's good! These questions have definitely reinforced my reading and made me feel like I really could begin to troubleshoot a network problem. Bravo!


      At the same time, and maybe your experience is the same, I take way longer to answer the Cisco Press questions, which in my opinion are several levels more difficult than the Boson ExSim Max questions.


      And so two questions, the second being your opinion on the question below, the first being anyone's experience with how the Cisco Press question compare in difficult to the real exam questions.


      Among the question's possible answers, all are reserved IP addresses, but two are not valid private IP addresses, according to RFC 1918. I think that's what we're supposed to take home there.


      The question's explanation could be improved, in my opinion, concerning the distinction between private and reserved.


      Is is not true that any 169.254 address is reserved, according to RFC 3927?


      Is it not also true that any 127 address is reserved, according to RFC 3330?


      But neither is a valid private address, seems to be the point of the question, I guess.


      Link-local addresses (RFC 3927):

      Loopback addresses (RFC 3330):



      Comments? Here is the question, verbatim:


      Cisco Press CCNA ICND 1 :: CD-I1-3-06-001-1


      Which of the following are reserved private IP addresses, according to RFC 1918.




      Correct Answers: C, D, E.


      "The RFC 1918 private network numbers are, Class Bs between and inclusive, and all Class C networks that begin with 192.168. All addresses that begin with 127 are reserved, but not as valid private IP addresses."

        • 1. Re: Private versus reserved IP addresses

          Yes, this is correct; this is how you should answerer question like this on exam;

          the key is that question is pointing out RFC 1918;

          even if it did not list RFC 1918 (unlikely), I would answer the same way;


          the point is that you can use (implement) ranges listed in RFC 1918, whereas you cannot use the other reserved spaces.

          • 2. Re: Private versus reserved IP addresses

            I like Martin's answer.  In addition, all five networks listed in the problem are "reserved" address spaces, but only three are reserved "private" address space.  The key points in this question are the words "private" and RFC 1918.


            Hope this helps.




            • 3. Re: Private versus reserved IP addresses

              Thank you, both! I'm glad I asked. "Reserved" versus "private" is a pretty important distinction.


              I wonder if it would it be appropriate to open a new discussion for input on my other question, about comparing the Boson ExSim-Max ICND1 questions with the questions that come with Odom's ICND1 text and are delivered through the same Boson engine. I would just be interested in anyone's input comparing level of challenge. I don't mind opening a new discussion so as not to clutter up this one.

              • 4. Re: Private versus reserved IP addresses

                new discussion tread is good idea 'cause of title of this one;


                you said you have Boson Exam-sim so this is not about buy or not;

                does exam-sim come with Sims or Simlet type of questions?


                what many practice engines are missing are those Simlets and Sim types.

                few years back, Transcender exams were  the best, better than Boson. I have not used either one for few years, so would not know which one is better.


                I think someone has passed CCNA recently and used Boson exams among ohter resources;

                if u search the forum, you may get info u want,


                Message was edited by: Martin

                • 5. Re: Private versus reserved IP addresses

                  Thank you, Martin.


                  The Boson Ex-Sim Max exams do come with sim questions. I am working the ICND1 Ex-Sim Max. There are 183 questions (with simlets considered as one question). The simulations I have all have something to do with troubleshooting IP connectivity. For example, PCs in different LANs cannot ping each other; go fix it. The emphasis is on show commands to discover that your router interfaces do not have IP addresses, or RIP isn't running, or RIP is running but not against all the networks, or there's an encapsulation mismatch, or the DCE router is missing a clock rate, or CHAP is set but the routers that need to authenticate have no logins - or all of those!


                  The practice questions that come with Odom's ICND1 book and which are also delivered through the Boson exam engine are much more difficult than the questions that come with the ICND1 Ex-Sim Max exam. The Cisco Press questions often tie together many chapters in the book and really make you analyze a scenario to determine an answer. (I am not complaining.) Beyond that, the answers are deliberately tricky in their phrasing, and you'll find some answers that are exactly right except the IP range includes the broadcast IP and should not (so you have to know subnetting cold).


                  Overall, I would say that the Cisco Press questions are several levels more difficult than the Boson questions. To put that in tangible terms: I achieved 90-95% on the Boson exams without a huge amount of pain but I am still struggling at the 75% level on the Cisco Press questions. And that's where my question about how either exam compares to the real exam came about.

                  • 6. Re: Private versus reserved IP addresses



                    Hello, Can you give me the exact answer for this question? Thanks.

                    • 7. Re: Private versus reserved IP addresses

                      It would be the and  Here is the range of private ip


                      A -

                      B -

                      C -

                      • 8. Re: Private versus reserved IP addresses

                        Just wanted to rectify a small typo.  The correct three blocks of the IP address space for private internets, as specified by RFC 1918, are:

                      -  (10/8 prefix)

                    -  (172.16/12 prefix)

                   - (192.168/16 prefix).

                        • 9. Re: Private versus reserved IP addresses

                          I know this is an old post but I just want throw in a simple method to identify the Private IP addresses in the exam.

                          1) All class A private IP addresses begin with 10 in the first octet

                          2) Any class B address that does not begin with 172 is a public address and any that begins with 172 in the first octet and a number less than 15 or greater than 32 in the second octet is a public address.

                          3) All class C private IP addresses have 192 in the first octet and 168 in the second octet.