Een paar voorbeelden:
Scenario 1 - Given a network address and subnet mask - How many subnets can you have and how many hosts per subnet.
Here we are given the address of: 172.16.0.0 /22
First we list the mask then the address in binary:
11111111 11111111 11111100 00000000 - (Subnet mask)
10101100 00010000 00000000 00000000 - (Address)
To calculate the number of subnets we total up the extra bits we are using in the mask, in this case its 6 (/22 = 8 + 8 + 6)
So as we are using 6 extra bits for the mask we can use the formula:
2 to the power of 6-2 or 2x2x2x2x2x2 = 64-2 =62 subnets
To calculate the number of hosts per subnet we total up the bits available for hosts, in this case its 10 (/22 from 32 total bits = 10)
So as we are using 10 bits for the host we can use the formula:
2 to the power of 10-2 or 2x2x2x2x2x2x2x2x2x2 = 1024-2 1022 hosts per subnet
Point to remember 2 to the power of bits used for either mask or hosts minus 2 will give you either the number of subnets or hosts per subnet
The more bits used for subnets the less bits available for hosts = more subnets - less hosts.
Scenario 2 - Given a network address calculate the customers requirements or subnets and hosts per network
Here we are given the address of: 172.16.0.0 and require 6 departments with 2000 hosts per department
First we list the mask then the address in binary:
11111111 11111111 00000000 00000000 - (Subnet mask)
10101100 00010000 00000000 00000000 - (Address)
As the first two octets are the default for this address type (255.255.0.0.) we go to the 3rd octet and start using bits there.
using 1 bit will give us 2 to the power of 1 or 2x1 =2-2 =0 Not enough
using 2 bits will give us 2 to the power of 2 or 2x2=4-2 =2 Not enough
using 3 bits will give us 2 to the power of 3 or 2x2x2=8-2 = 6 Enough
As we used 3 bits there are 13 bits left (5 from one octet 8 from the other) for hosts so 2 to the power of 13 = 8192-2 =8190 Enough for our hosts
En meer op de source:
Subnetting
