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Access list - wildcards

VantageUKVantageUK Member Posts: 111
The Lammle book has me a little confused on the wildcards.

He has 172.16.16.0 0.0.3.255 as covering 172.16.16.0 through 172.16.19.0. Does he mean 172.16.16.0 - 172.16.19.255?

Same with 172.16.16.0 0.0.7.255 as covering 172.16.16.0 through 172.16.23.0. Does he mean 172.16.16.0 - 172.16.23.255

Cheers

Charlie.

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    tech-airmantech-airman Member Posts: 953
    VantageUK,
    VantageUK wrote: »
    The Lammle book has me a little confused on the wildcards.

    He has 172.16.16.0 0.0.3.255 as covering 172.16.16.0 through 172.16.19.0. Does he mean 172.16.16.0 - 172.16.19.255?

    What is the wildcard mask of 0.0.3.255 in binary?
    VantageUK wrote: »
    Same with 172.16.16.0 0.0.7.255 as covering 172.16.16.0 through 172.16.23.0. Does he mean 172.16.16.0 - 172.16.23.255

    What is the wildcard mask of 0.0.7.255 in binary?
    VantageUK wrote: »
    Cheers

    Charlie.
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    VantageUKVantageUK Member Posts: 111
    I'm not sure what you're asking.

    Well, to rephrase, I know what you're asking, but I'm not sure why you're asking it?

    What I'm after is when Lammle says a wildcard covers networks 172.16.16.0 through 172.16.19.0, does he mean that it covers ALL of the available IPs in the networks?

    ie: all the way up to 172.16.19.255.
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    tech-airmantech-airman Member Posts: 953
    VantageUK wrote: »
    I'm not sure what you're asking.

    Well, to rephrase, I know what you're asking, but I'm not sure why you're asking it?

    What I'm after is when Lammle says a wildcard covers networks 172.16.16.0 through 172.16.19.0, does he mean that it covers ALL of the available IPs in the networks?

    ie: all the way up to 172.16.19.255.

    VantageUK,

    If you know what I'm asking, feel free to answer my questions.
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    mzinzmzinz Member Posts: 328
    VantageUK wrote: »
    I'm not sure what you're asking.

    Well, to rephrase, I know what you're asking, but I'm not sure why you're asking it?

    What I'm after is when Lammle says a wildcard covers networks 172.16.16.0 through 172.16.19.0, does he mean that it covers ALL of the available IPs in the networks?

    ie: all the way up to 172.16.19.255.

    The problem is that you're thinking about subnetworks as ALWAYS having 255 hosts. This isn't always the case. A subnet will only have 255 hosts if it is 255.255.255.0 (or 0.0.0.255 in this case).

    The size of a subnet depends on the network mask, right?

    The reason that Vantage was having you convert to binary is because you can determine how many hosts are in a subnet by doing so.

    0.0.3.255 in binary = 0000000.00000000.00000011.11111111

    Ok, so we know that 0 bits are part of the subnet. Now let's convert that IP to binary.

    172.16.16.0 in binary = 10101100.00010000.00010000.00000000

    Now, any spot in the wildcard mask that has a 0 is part of the SUBNET.
    10101100.00010000.00010000.00000000 = 172.16.16.0 <----Network address
    00000000.00000000.00000011.11111111 = 0.0.3.255 <----Wildcard mask
    10101100.00010000.00010000.00000000 = 172.16.16.0 <----Subnet Start
    10101100.00010000.00010011.11111111 = 172.16.19.255 <----Subnet End

    See what we did there? Now, keep in mind, this is ONE SUBNET! So theoretically you could use any IP from 172.16.16.1 to 162.16.19.254!

    So lets say you just wanted to calculate how many hosts are in this single subnet. You can do that JUST by having the wildcard mask (or subnet address)!
    0.0.3.255 = 00000000.00000000.00000011.11111111. Ok, so that is TEN 1's in a row. Using simple binary, let's calculate what that comes out to:
    2, 4, 8, 16, 32, 64, 128, 256, 512, 1024 <
    Ten bits in binary equals 1024!! That means that we have 1022 usable IPs (one for subnet and one for broadcast)!
    _______LAB________
    2x 2950
    2x 3550
    2x 2650XM
    2x 3640
    1x 2801
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