# File subnetting procedure

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23 Οκτ 2013 (πριν από 4 χρόνια και 6 μήνες)

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Subnetting Procedure

This procedure assumes you are beginning with a Class C address block and
must subnet the block to meet the needs of a scenario.

1. Read the scenario. Determine the total number of networks and the
maximum number of hosts in each network. Example: you need to create 6 networks; the largest has 20 hosts.

2. Decide how many bits to borrow from the host portion. Use the formulae.
You can create up to 2
n
networks where n is the number of bits you
borrow. This will provide 2
h
-2 hosts per network where h is the number of
host bits remaining.
Example: Borrow 3 bits from the host portion. This provides 8 networks
(2
3
= 8) and 30 hosts per network (2
5
-2 = 30).

3. Determine the prefix length and subnet mask based on the borrowed bits.
Example: Since we’re borrowing 3 bits, our prefix changes from /24 to /27.

4. Find the “network multiple” by finding the binary value of the last borrowed
bit. To do this, create a binary octet where only the n
th
digit is a 1 where n
is the number of bits you have borrowed from the host portion. The
decimal value of this octet is the network multiple.
Example: Since we have borrowed 3 digits, create the octet 00100000.
The network multiple is 32.

5. Write out network addresses in series using the network multiple to create
the final octet. Start with 0 and add the multiple for each network until you
run out of space.
Example: The network multiple is 32. Therefore the 8 network addresses
will have the final octets: 0, 32, 64, 96, 128, 160, 192, 224.

6. Use the list of network addresses to determine any address in the
scenario, keeping in mind that for any given network, the first address is