Subnetting 122.22.0.0 /22 query

black_lionblack_lion Registered Users Posts: 4 ■□□□□□□□□□
in CCNA & CCENT
Hi all. I have been given the address: 122.22.0.0 /22 which in binary is 01111010.00010110.00000000.00000000 (bold is 10 bits left for hosts)

and its subnet mask is 255.255.252.0 in binary is 11111111.11111111.11111100.00000000

I am trying to calculate new subnet address when 8 bits left for host (this is a network prefix of /24)

This is what I did:

122.22.0.0 converted to binary with network prefix of /24 is:

01111010.00010110.00000000.00000000 (bold shows 8 bits left for host)

and in decimal new subnet address from my understanding is 122.22.0.0 /24

but correct answer is 122.22.2.0 /24

Why does the 3rd octet is 2 and not 0?
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Comments

  • 10Linefigure10Linefigure Member Posts: 368 ■■■□□□□□□□
    If you have a /24 then your entire last octet is open to hosts. Having your /22 allows for 255.255.252.0 so you have 3.254 as your block size, this allows you to break your Vlans and manage IP's much easier then a /8 , /16, /24 because they leave all the rest as host bits and give you less to work with.
    CCNP R&S, Security+
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  • bobfromfplbobfromfpl Member Posts: 104
    If the network prefix is really 01111010.00010110.00000000 (122.22.0) then sounds like the answer is wrong and your initial guess was correct.
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  • Magic JohnsonMagic Johnson Member Posts: 414
    bobfromfpl wrote: »
    If the network prefix is really 01111010.00010110.00000000 (122.22.0) then sounds like the answer is wrong and your initial guess was correct.

    I was thinking that, maybe no subnet zero configured or something but then that would be 122.22.1 instead of 2.
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  • bobfromfplbobfromfpl Member Posts: 104
    Yeah, I guess that's a valid assumption but he didn't mention IOS, just subnetting.
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  • Magic JohnsonMagic Johnson Member Posts: 414
    bobfromfpl wrote: »
    Yeah, I guess that's a valid assumption but he didn't mention IOS, just subnetting.

    Lol sorry I'm still in Pearson test mode of looking out for gotchas!
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  • vasyvasyvasyvasy Member Posts: 68 ■■■□□□□□□□
    You should be able to use 4 x /24 subnets, like this:

    122.22.0.0/24
    122.22.1.0/24
    122.22.2.0/24
    122.22.3.0/24

    So your answer is correct, but their answer is also correct :)
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  • black_lionblack_lion Registered Users Posts: 4 ■□□□□□□□□□
    vasyvasy wrote: »
    You should be able to use 4 x /24 subnets, like this:

    122.22.0.0/24
    122.22.1.0/24
    122.22.2.0/24
    122.22.3.0/24

    So your answer is correct, but their answer is also correct :)

    Why are they both the same? Im a bit confused :/
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  • bobfromfplbobfromfpl Member Posts: 104
    black_lion wrote: »
    Why are they both the same? Im a bit confused :/


    The subnets are different, they just use the same subnet mask.
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  • MinaryMinary Member Posts: 74 ■■□□□□□□□□
    We aren't seeing the question properly. The OP has misquoted it a bit.
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