Another subnetting calculation question...Scott?
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Posted by on October 2, 2008, 11:45 am
Please log in for more thread options Okay, I've learned how to take an IP address and mask and determine the network address. I know 2 methods: The "Magic Number" easy method from Odom's videos, and the binary AND method which I use to check my answer. So then we move on to determining the broadcast address, as well as host range. We learned yet another "Magic Number" method: Magic Number plus relevant octet of network address, minus 1. Example: Mask: 255.255.224.0 IP: 128.200.100.100 Network: 128.200.96.0 (Easy: 256 - 224 = 32. 96 is the multiple of 32 without going over 100, so it's 96). Binary ANDing 224 and 100 is just as easy. 1st usable host IP: 128.200.96.1. Again, simple. Network address +1. Now: We're taught that to find the broadcast address, take 96, add the magic number (32) = 128, subtract 1, and we get 127. Simple enough to memorize, but doesn't satisfy me. How do we get there the "hard" way, without using a formula? I'm assuming there's a binary method to get from the network or IP address to the broadcast address? | |||||||||||||
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Posted by Inga Mewes on October 11, 2008, 8:06 am
Please log in for more thread options The Binary Method for getting the Broadcast Address is to set all host bits int the IP/network Address to 1. Example: Network 192.168.1.160/29 i.e 255.255.255.248 Binary: 11000000.10101000.00000001.10100000 Netmask: 11111111.11111111.11111111.11111000 so setting the last 3 bits in the binary represantation of your IP address/Network address leaves you with: Binary: 11000000.10101000.00000001.10100111 which is the correct broadcast address: 192.168.1.167 Mitch@_._ schrieb: | |||||||||||||
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Posted by on October 11, 2008, 11:06 am
Please log in for more thread options
>The Binary Method for getting the Broadcast Address is to set all host
>bits int the IP/network Address to 1. Thanks! That's exactly what I was looking for. | |||||||||||||
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> the network address. I know 2 methods: The "Magic Number" easy
> method from Odom's videos, and the binary AND method which I use to
> check my answer.
>
> So then we move on to determining the broadcast address, as well as
> host range. We learned yet another "Magic Number" method: Magic
> Number plus relevant octet of network address, minus 1.
>
> Example:
>
> Mask: 255.255.224.0
> IP: 128.200.100.100
> Network: 128.200.96.0 (Easy: 256 - 224 = 32. 96 is the multiple of
> 32 without going over 100, so it's 96). Binary ANDing 224 and 100 is
> just as easy.
>
> 1st usable host IP: 128.200.96.1. Again, simple. Network address
> +1.
>
> Now: We're taught that to find the broadcast address, take 96, add
> the magic number (32) = 128, subtract 1, and we get 127.
>
> Simple enough to memorize, but doesn't satisfy me.
> How do we get there the "hard" way, without using a formula?
>
> I'm assuming there's a binary method to get from the network or IP
> address to the broadcast address?