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Please elaborarte on Class B private addresses

DescendedDescended Member Posts: 7 ■□□□□□□□□□
in CCNA & CCENT
So Class B private range is 172.16.0.0 -172.31.0.0 which is mask of 12
So it gives you 2^12 networks which is 4096
and
It also gives you 2^20 which is 1048576. -2 hosts

Does it mean that each of those 4096 networks contain 1048574 hosts
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    PristonPriston Member Posts: 999 ■■■■□□□□□□
    If you are give a /12 that is 1 network. 172.16.0.0 - 172.31.0.0
    You can subnet the /12 to be multiple subnets to give you more networks

    The first 12 bits in a /12 are NOT yours to play with, if I give you 172.16.0.0/12 you can't use 8.10.20.0
    | - Not yours - ||
    Yours
    |
    |xxxxxxxx.xxxx||0000.00000000.00000000|

    If i'm given 172.16.0.0/12, I can use a subnet mask of /24 and have 4096 networks with 254 hosts
    | - Not yours - || - Networks - || - Hosts - |
    |xxxxxxxx.xxxx||1111.11111111||.00000000|
    A.A.S. in Networking Technologies
    A+, Network+, CCNA
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    DescendedDescended Member Posts: 7 ■□□□□□□□□□
    Sorry I get it now

    172.16.0.0's host bits are 0.0 which is 65536 - 2 = 65534 host addresses
    and for 172.31.0.0 - 172.16.0.0, 16 contagious networks we have 16 x 65534 = 1048544 hosts between those networks
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    DescendedDescended Member Posts: 7 ■□□□□□□□□□
    I was talking about RFC 1918, which defines non-routable class A, B and C
    This is a bit confusing as we have mask incrementing in 4
    10.0.0.0 - 10.255.255.255 /8
    172.16.0.0 - 172.31.0.0 /12 (which is 8 + 4)
    192.168.0.0 - 192.168.255.255 /16 (which is 12 + 4)
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    phdillardphdillard Member Posts: 86 ■■□□□□□□□□
    I think you're confused about the masks. Assuming classful addressing is being used, your 10. network is a /8, but your 172.16-32 is a /16, and 192.168 is a /24. Anything between 8, 16, 24, and 32 is subnetting, which is classless, and your mask no longer conforms to A,B,C because you are borrowing bits from the host portion to create subnets (2 subnets for each bit borrowed) and reducing the number of hosts addresses available.
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    PristonPriston Member Posts: 999 ■■■■□□□□□□
    Private network - Wikipedia, the free encyclopedia



    [TH="bgcolor: #F2F2F2, align: center"]RFC1918 name[/TH]
    [TH="bgcolor: #F2F2F2, align: center"]IP address range[/TH]
    [TH="bgcolor: #F2F2F2, align: center"]number of addresses[/TH]
    [TH="bgcolor: #F2F2F2, align: center"]largest CIDR block (subnet mask)[/TH]
    [TH="bgcolor: #F2F2F2, align: center"]host id size[/TH]
    [TH="bgcolor: #F2F2F2, align: center"]mask bits[/TH]
    [TH="bgcolor: #F2F2F2, align: center"]classful description[/TH]


    24-bit block
    10.0.0.0 - 10.255.255.255
    16,777,216
    10.0.0.0/8 (255.0.0.0)
    24 bits
    8 bits
    single class A network


    20-bit block
    172.16.0.0 - 172.31.255.255
    1,048,576
    172.16.0.0/12 (255.240.0.0)
    20 bits
    12 bits
    16 contiguous class B networks


    16-bit block
    192.168.0.0 - 192.168.255.255
    65,536
    192.168.0.0/16 (255.255.0.0)
    16 bits
    16 bits
    256 contiguous class C networks

    A.A.S. in Networking Technologies
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    theodoxatheodoxa Member Posts: 1,340 ■■■■□□□□□□
    You could subnet 172.16.0.0/12 into anything from /13 to /30. That said, I have never seen it broken into anything larger than /16. I personally use a /23 at my Condo and a different /23 at my Parent's House - I renumbered their network [so the two networks wouldn't overlap] when I setup a VPN.
    R&S: CCENT → CCNA → CCNP → CCIE [ ]
    Security: CCNA [ ]
    Virtualization: VCA-DCV [ ]
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