Use Magic Number to Find Resident Subnet
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Finding Resident Subnet 128 64 32 16 8 4 2 1 1. Write in dotted decimal notation (IP addy and Subnet) 128.200.100.100 with Subnet 255.255.224.0/19 would be: 10000000.11001000.01100100.01100100 and Subnet 11111111.11111111.11100000.00000000 2. Draw table with available information for Subnet Mask, IP Addy, Subnet #: Subnet Mask 255 255 224 0 IP Addy 128 200 100 100 Subnet # 3. Draw rectangle around column that includes the INTERESTING OCTET (* INTERESTING OCTETS do not include 0 or 255): Subnet Mask 255 255 224 0 IP Addy 128 200 100 100 Subnet # 4. a) Octets to the left are copied from IP Addy b) Octets to the right are 0’s Subnet Mask 255 255 224 0 IP Addy 128 200 100 100 Subnet # 128 200 0 5. To determine the value of the INTERESTING OCTET, calculate the MAGIC NUMBER (256 – the mask’s value in the Subnet Mask’s INTERESTING OCTET block. 256 – 224 = 32
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Subnetting
Transcript of Use Magic Number to Find Resident Subnet
Finding Resident Subnet
128 64 32 16 8 4 2 1
1. Write in dotted decimal notation (IP addy and Subnet)128.200.100.100 with Subnet 255.255.224.0/19 would be:10000000.11001000.01100100.01100100 and Subnet 11111111.11111111.11100000.00000000
2. Draw table with available information for Subnet Mask, IP Addy, Subnet #:
Subnet Mask 255 255 224 0IP Addy 128 200 100 100Subnet #
3. Draw rectangle around column that includes the INTERESTING OCTET (* INTERESTING OCTETS do not include 0 or 255):
Subnet Mask 255 255 224 0IP Addy 128 200 100 100Subnet #
4. a) Octets to the left are copied from IP Addyb) Octets to the right are 0’s
Subnet Mask 255 255 224 0IP Addy 128 200 100 100Subnet # 128 200 0
5. To determine the value of the INTERESTING OCTET, calculate the MAGIC NUMBER (256 – the mask’s value in the Subnet Mask’s INTERESTING OCTET block.
256 – 224 = 32
6. Using your result, use integers of this value to locate the number that is closest to the IP Addy INTERESTING OCTET value (but make sure it isn’t greater than the octet’s value):
32 … 64 … 96 … 128 …160 …
Subnet Mask 255 255 224 0
The answer is: 96
IP Addy 128 200 100 100Subnet # 128 200 96 0
