Boson exam question

jwillsjwills Posts: 44Member ■■□□□□□□□□
I am stumped on a boson exam question. There are 4 router on a lan. Three of the routers f0/0 interface are all in the same subnet. (10.2.0.0 255.255.224.0) Boson is saying that if a fourth Router has an interface in a different subnet 10.2.33.4/19 that it would not be able to ping one of the other routers interface. (Stating because its in another subnet.)

Please help me understand what i am missing. I have a .doc file with a screenshot.

Comments

  • abefromanabefroman Posts: 278Banned
    jwills wrote: »
    I am stumped on a boson exam question. There are 4 router on a lan. Three of the routers f0/0 interface are all in the same subnet. (10.2.0.0 255.255.224.0) Boson is saying that if a fourth Router has an interface in a different subnet 10.2.33.4/19 that it would not be able to ping one of the other routers interface. (Stating because its in another subnet.)

    Please help me understand what i am missing. I have a .doc file with a screenshot.

    I think that since all those routers are essentially connected together (through a switch), the IP for their ethernet port going to the switch has to be all on the same subnet.

    If you made a sub-interface with the ip 10.2.33.4/19 or make f0/1 that ip, and advertised that network, then it would ping.
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  • chXchX Posts: 100Member ■■■□□□□□□□
    Here's my interpretation of the question.

    I'm guessing the answers highlighted in yellow are correct.

    IP addressing:

    R1 fa0/0 - 10.2.19.1 255.255.224.0
    R2 fa0/0 - 10.2.1.2 255.255.224.0
    R3 fa0/0 - 10.2.15.3 255.255.224.0

    Now, if you quickly reverse engineer that subnet you'll find out the ranges are:

    10.2.0.0 - 10.2.31.255
    10.2.32.0 - 10.2.63.255
    10.2.64.0 - 10.2.95.255
    10.2.96.0 - 10.2.127.255
    10.2.128.0
    etc

    All of those IPs are in the same subnet: 10.2.0.0 - 10.2.31.255.

    So, assuming layer1 and layer2 are working correctly (which the question states), a ping from R1 to R3's fa0 will work.

    That answers the first question.

    The next correct answer states that configuring 10.2.31.1 255.255.255.0 on R2's fa0/1 interface would be rejected.

    10.2.31.1 is in the 10.2.0.0 - 10.2.31.255 subnet, and having two interfaces on a router in the same subnet *shouldn't* occur.
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  • notgoing2failnotgoing2fail Posts: 1,138Member
    chX wrote: »
    Here's my interpretation of the question.

    I'm guessing the answers highlighted in yellow are correct.

    IP addressing:

    R1 fa0/0 - 10.2.19.1 255.255.224.0
    R2 fa0/0 - 10.2.1.2 255.255.224.0
    R3 fa0/0 - 10.2.15.3 255.255.224.0

    Now, if you quickly reverse engineer that subnet you'll find out the ranges are:

    10.2.0.0 - 10.2.31.255
    10.2.32.0 - 10.2.63.255
    10.2.64.0 - 10.2.95.255
    10.2.96.0 - 10.2.127.255
    10.2.128.0
    etc

    All of those IPs are in the same subnet: 10.2.0.0 - 10.2.31.255.

    So, assuming layer1 and layer2 are working correctly (which the question states), a ping from R1 to R3's fa0 will work.

    That answers the first question.

    The next correct answer states that configuring 10.2.31.1 255.255.255.0 on R2's fa0/1 interface would be rejected.

    10.2.31.1 is in the 10.2.0.0 - 10.2.31.255 subnet, and having two interfaces on a router in the same subnet *shouldn't* occur.

    CHX is correct here.

    I just worked it out myself and the only answers are A and D.

    On the last one with 10.2.31.1, the subnet mask is wrong so it would overlap with the 10.2.0.0 /19 subnet and get rejected.
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