Subnetting question

EssendonEssendon Member Posts: 4,546 ■■■■■■■■■■
in Net Infra 70-291
Question in the MS Press book, page 2-44. I know I should I've been able to answer this myself, but it's been a year and a few months since my CCNA icon_redface.gif . So here goes:

You have a 192.168.64.0/23 address block that you need to subnet as 192.168.64.0/25. The answer on the same page lists 4 subnets, 192.168.64.0, 192.168.64.128, 192.168.65.0, 192.168.65.128. I know where the first 2 came from, but how did the last 2 appear in the answer.

I am definitely missing something here, could someone please help.

Edit: I'll add three more questions here.

1. We can use the calculator during the test, right?
2. Can there be VLSM questions on the test? Transcender has a huge (really huge) question on VLSM.
3. How extensively can RIP and OSPF be on the test. The questions at the back of the MS Press are fairly in-depth, the CCNA stuff.

I hope asking these questions is not in violation of the test DNA, sorry NDA. I just want a general idea.
NSX, NSX, more NSX..

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Comments

  • flares2flares2 Member Posts: 79 ■■□□□□□□□□
    Remember your splitting one network into multiple subnets. Your 192.168.64.0/23 network has a range of 192.168.64.1-192.168.65.255. So, you can split this into 4 /25 subnets.
    It looks like you're seeing the /25 subnets as Class C. Remember your network is /23, which is class B.
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  • meadITmeadIT Member Posts: 581 ■■■■□□□□□□
    MobilOne wrote:
    1. We can use the calculator during the test, right?
    2. Can there be VLSM questions on the test? Transcender has a huge (really huge) question on VLSM.
    3. How extensively can RIP and OSPF be on the test. The questions at the back of the MS Press are fairly in-depth, the CCNA stuff.

    I hope asking these questions is not in violation of the test DNA, sorry NDA. I just want a general idea.

    1. Yes, but they are not scientific calculators, just the basic functions (add, subtract, multiply, divide)..no binary conversions.

    2. Yes, definately.

    3. I don't remember if I had any RIP or OSPF on my exam, so I'll leave this up to someone else.
    CERTS: VCDX #110 / VCAP-DCA #500 (v5 & 4) / VCAP-DCD #10(v5 & 4) / VCP 5 & 4 / EMCISA / MCSE 2003 / MCTS: Vista / CCNA / CCENT / Security+ / Network+ / Project+ / CIW Database Design Specialist, Professional, Associate
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  • EssendonEssendon Member Posts: 4,546 ■■■■■■■■■■
    flares2 wrote:
    So, you can split this into 4 /25 subnets.

    Can I ask how?
    NSX, NSX, more NSX..

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  • dynamikdynamik Banned Posts: 12,312 ■■■■■■■■■□
    I'll give you a hint ;)

    Starting Network Mask: 11111111.11111111.11111110.00000000
    Available Subnet Bits: 11111111.11111111.11111110.00000000
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  • meadITmeadIT Member Posts: 581 ■■■■□□□□□□
    You have a 192.168.64.0/23 address block that you need to subnet as 192.168.64.0/25. The answer on the same page lists 4 subnets, 192.168.64.0, 192.168.64.128, 192.168.65.0, 192.168.65.128. I know where the first 2 came from, but how did the last 2 appear in the answer.

    Ok, let's break the 3rd and 4th octet into binary. The network portion is in blue.

    192.168.64.0/23 = 192.168.01000000.00000000

    If you want to subnet it into /25, then you will borrow 2 bits for the subnet (subnet portion in bold).

    192.168.64.0/25 = 192.168.01000000.00000000

    So our possible subnets could be 00, 01, 10, 11, so that gives us the network addresses

    192.168.01000000.00000000 = 192.168.64.0
    192.168.01000000.10000000 = 192.168.64.128
    192.168.01000001.00000000 = 192.168.65.0
    192.168.01000001.10000000 = 192.168.65.128
    CERTS: VCDX #110 / VCAP-DCA #500 (v5 & 4) / VCAP-DCD #10(v5 & 4) / VCP 5 & 4 / EMCISA / MCSE 2003 / MCTS: Vista / CCNA / CCENT / Security+ / Network+ / Project+ / CIW Database Design Specialist, Professional, Associate
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  • EssendonEssendon Member Posts: 4,546 ■■■■■■■■■■
    XtreemeChaos wrote:
    You have a 192.168.64.0/23 address block that you need to subnet as 192.168.64.0/25. The answer on the same page lists 4 subnets, 192.168.64.0, 192.168.64.128, 192.168.65.0, 192.168.65.128. I know where the first 2 came from, but how did the last 2 appear in the answer.

    Ok, let's break the 3rd and 4th octet into binary. The network portion is in blue.

    192.168.64.0/23 = 192.168.01000000.00000000

    If you want to subnet it into /25, then you will borrow 2 bits for the subnet (subnet portion in bold).

    192.168.64.0/25 = 192.168.01000000.00000000

    So our possible subnets could be 00, 01, 10, 11, so that gives us the network addresses

    192.168.01000000.00000000 = 192.168.64.0
    192.168.01000000.10000000 = 192.168.64.128
    192.168.01000001.00000000 = 192.168.65.0
    192.168.01000001.10000000 = 192.168.65.128

    Thank you, that's cleared the mystery up :D
    NSX, NSX, more NSX..

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  • the_erickeethe_erickee Member Posts: 74 ■■□□□□□□□□
    XtreemeChaos wrote:
    You have a 192.168.64.0/23 address block that you need to subnet as 192.168.64.0/25. The answer on the same page lists 4 subnets, 192.168.64.0, 192.168.64.128, 192.168.65.0, 192.168.65.128. I know where the first 2 came from, but how did the last 2 appear in the answer.

    Ok, let's break the 3rd and 4th octet into binary. The network portion is in blue.

    192.168.64.0/23 = 192.168.01000000.00000000

    If you want to subnet it into /25, then you will borrow 2 bits for the subnet (subnet portion in bold).

    192.168.64.0/25 = 192.168.01000000.00000000

    So our possible subnets could be 00, 01, 10, 11, so that gives us the network addresses

    192.168.01000000.00000000 = 192.168.64.0
    192.168.01000000.10000000 = 192.168.64.128
    192.168.01000001.00000000 = 192.168.65.0
    192.168.01000001.10000000 = 192.168.65.128

    Great explaination!!!
    Erick Marshall - @erickbm

    MCSE,MCITP x2,vExpert 2015,VCAP,VCP5 x2,MCSA x2,MCTS x3,MCP x2,UCP,Network+,A+
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  • PsoasmanPsoasman Member Posts: 2,687 ■■■■■■■■■□
    There is a good chance you will be tested on these. I would know how to set these up, when you would use them. OSPF is harder to set up, but is dynamic and easier to maintain once set up and is used by larger companies.
    RIP is still used in smaller companies. IT is easier to set up, but harder to maintain. There is a 15-hop limit with RIP v1.
    RIP v1has been around since the late 60's when the goverment started the internet aka ARPANET....not AL GORE!!

    I think I only had a couple of questions on this. Main focus was DNS
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