IP Subnet Calculator

jwillsjwills Member Posts: 44 ■■□□□□□□□□
in CCNA & CCENT
If you have a subnet mask of 255.255.255.224 using the IP address of 192.100.60.0, wouldn't it come out giving you 6 subnets. (Using the 2 to 3rd power minus 2 formula). And the first subnet would be 192.100.60.32, right?
I'm asking because the subnet calulator only gave me the choice of 8 subnets, and 192.100.60.0 being the first subnet.
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  • mikearamamikearama Member Posts: 749
    Since all current IOS's allow IP Subnet Zero, you would get 8 subnets, the first usable one being 192.100.60.0.

    2**n - 2 is still the standard formula when tallying ip address for nodes, but 2**n is now the preferred method of determining number of subnets.

    Mike
    There are only 10 kinds of people... those who understand binary, and those that don't.

    CCIE Studies: Written passed: Jan 21/12 Lab Prep: Hours reading: 385. Hours labbing: 110

    Taking a time-out to add the CCVP. Capitalizing on a current IPT pilot project.
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  • PashPash Member Posts: 1,600 ■■■■■□□□□□
    Ohh no not again! (fetches hard hat)

    mikearama is correct all latest IOS's support ip subnet zero which means all 1's and all 0's subnet bits are ok. lets not speculate anymore, let's just say Cisco arent cruel, they will always state whether it is on or off when asking you a schema question....there will only be one answer that is correct...so don't panic.

    Cheers,
    DevOps Engineer and Security Champion. https://blog.pash.by - I am trying to find my writing style, so please bear with me.
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  • WebmasterWebmaster Admin Posts: 10,292 Admin
    Besides the CCNA exam (please do read our CCNA FAQ Sticky in this forum), I deliberately didn't built-in a 'disable subnet-zero and all 1s broadcast' option because the name would be too long... err.. seriously, because it's legacy. Again see sticky, this one is going to be locked.
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