Training test question

jekylljekyll Posts: 6Member ■■□□□□□□□□
Which one of the following IP addresses is NOT assignable to a machine in a network?
a) 193.158.20.254
b) 54.1.0.0
c) 137.4.0.0
d) 192.178.0.254

Answer: C)

Why? What are the steps to come to that conclusion?

Comments

  • JDMurrayJDMurray Certification Invigilator Surf City, USAPosts: 11,337Admin Admin
    Maybe the C answer option is supposed to read "127.4.0.0". No 127.0.0.0/8 IP address should be directly assignable to an IP interface.
  • EANxEANx Posts: 1,041Member ■■■■■■■□□□
    C is a class B address where the first two octets identify the network. Since none of the remaining bits are set, the all 0s indicates the network address for that subnet mask.
  • kaijukaiju Posts: 392Member ■■■■■■□□□□
    **Beware** It seems like that is a VCE **** question. I just corrected a VCE for a friend because I felt sorry for him. 25% of the questions were poorly worded, contained typos that made the question not answerable or the supposed correct answer actually was not correct.

    If you have the time and money I will suggest getting the Pearson test prep or Boson.

    Back to the question. I agree with JDMurray. 127.0.0.0/8 or 127.0.0.0 ~ 127.255.255.255 is the special used IPV4 loopback address network that will never be assigned to an interface.


    Work smarter NOT harder! Semper Gumby!
  • jekylljekyll Posts: 6Member ■■□□□□□□□□
    edited July 17
    EANx said:
    C is a class B address where the first two octets identify the network. Since none of the remaining bits are set, the all 0s indicates the network address for that subnet mask.
    I think you are right.
    In that case, and if I understood correctly, the following IP addresses wouldn't be valid either because they are also network addresses:
    54.0.0.0 (Class A)
    137.192.0.0 (Class B)
    192.192.192.0 (Class C)
    I made up these three addresses just to provide an example of what you are saying. This type of question is just about counting the octets of the default subnet mask and check if the IP addresses have an extra number outside the subnet mask octets or not. 

    Thank you and thanks to the others for participating also.
  • kaijukaiju Posts: 392Member ■■■■■■□□□□
    I made the "trick quick question assumption w/o really looking at the question. Now that I look at it, if you cannot visualize the answer a glance it is best to apply the base /16 subnet mask for class B and then do the math:

    100001000.00000100.00000000.00000000 binary for 137.4.0.0
    11111111.11111111.00000000.00000000 binary for /16
    all bits in the address after the 16th are flipped to "0" to ascertain the network address and the same bits after the 16th are flipped to "1" to get the broadcast address. 

    provides ip space for
    100001000.000001000.00000000.00000000 - 100001000.00000111.11111111.11111111
    137.4.0.0 - 137.7.255.255




    Work smarter NOT harder! Semper Gumby!
  • lwwarnerlwwarner Posts: 147Member ■■■□□□□□□□
    IMO, the question is bogus. Given an appropriate mask, 137.4.0.0 is a perfectly valid IP address. For example, 137.4.0.0/13 works just fine:

    2620-TS-FRS#sh run
    ...
    !
    interface FastEthernet0/0
     ip address 137.4.0.0 255.248.0.0
     duplex auto
     speed auto
    !
    ...

    2620-TS-FRS#sh ip int br
    Interface                  IP-Address      OK? Method Status                Protocol
    FastEthernet0/0            137.4.0.0       YES manual up                    up    
    Serial0/0                  unassigned      YES NVRAM  administratively down down  
    Serial0/1                  unassigned      YES NVRAM  down                  down  
    Serial0/2                  unassigned      YES NVRAM  down                  down  
    Serial0/3                  unassigned      YES NVRAM  down                  down  
    Loopback0                  101.101.101.101 YES NVRAM  up                    up          
    2620-TS-FRS#ping 137.4.0.0

    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 137.4.0.0, timeout is 2 seconds:
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms
    2620-TS-FRS#ping 137.4.0.1

    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 137.4.0.1, timeout is 2 seconds:
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms


    Bills-MacBook-Pro:~ lww$ ping 137.4.0.0
    PING 137.4.0.0 (137.4.0.0): 56 data bytes
    64 bytes from 137.4.0.0: icmp_seq=0 ttl=255 time=1.223 ms
    64 bytes from 137.4.0.0: icmp_seq=1 ttl=255 time=1.127 ms
    64 bytes from 137.4.0.0: icmp_seq=2 ttl=255 time=1.207 ms
    64 bytes from 137.4.0.0: icmp_seq=3 ttl=255 time=1.166 ms
    64 bytes from 137.4.0.0: icmp_seq=4 ttl=255 time=1.125 ms
    64 bytes from 137.4.0.0: icmp_seq=5 ttl=255 time=1.210 ms
    64 bytes from 137.4.0.0: icmp_seq=6 ttl=255 time=1.156 ms
    64 bytes from 137.4.0.0: icmp_seq=7 ttl=255 time=1.154 ms
    64 bytes from 137.4.0.0: icmp_seq=8 ttl=255 time=1.182 ms
    ^C
    --- 137.4.0.0 ping statistics ---
    9 packets transmitted, 9 packets received, 0.0% packet loss
    round-trip min/avg/max/stddev = 1.125/1.172/1.223/0.034 ms


    As you can see, 137.4.0.0 can, in fact, be assigned "to a machine in a network." FYI, the output above is from a real router (137.4.0.0) and a real laptop (137.4.0.1). This is just one of those things that works as expected in the real world, but doesn't work in PT.

    Really, CIDR has been around since 1992, can't we just forget about IP address classes already?

  • JDMurrayJDMurray Certification Invigilator Surf City, USAPosts: 11,337Admin Admin
    lwwarner said:
    IMO, the question is bogus. Given an appropriate mask, 137.4.0.0 is a perfectly valid IP address. For example, 137.4.0.0/13 works just fine:

    ...

    Really, CIDR has been around since 1992, can't we just forget about IP address classes already?

    This was my reasoning in thinking that the 137.4.0.0 answer option was a typo. Almost any IP address can be valid to assign to an interface given the ability to change the netmask. However, no netmask is given in this exam item, so we must assume the default (class-based) mask for each IP address given.

    There is some excellent thought happening in this discussion. Keep it up, people! :D
  • lwwarnerlwwarner Posts: 147Member ■■■□□□□□□□
    Hi JD, I'm glad to see some familiar names are still here! I haven't been active here in a long time, but I'm gearing up to recertify before February so I'm back. Hopefully I can learn & contribute along the way!

    I'm not sure what I think about being tagged as an "Ancient Member" though... :o
  • JDMurrayJDMurray Certification Invigilator Surf City, USAPosts: 11,337Admin Admin
    Dude, you and I are both "ancient" on this board!  :s
  • kaijukaiju Posts: 392Member ■■■■■■□□□□
    I do agree that the absence of a mask requires the use of assumption to derive an answer. Totally unnecessary question. 
    Work smarter NOT harder! Semper Gumby!
Sign In or Register to comment.