Transcript Exploits and System Security 1

IP Addressing
Learn to Subnet In a
single Slideshow
The Binary
(This is not as hard as it looks)
If we take our imaginary network of
208.98.1.0 and convert it to binary:
11010000.01100010.00000001.00000000
Now we can sub-divide this network into
smaller networks. We have 8 bits
available in the ‘host’ portion of this
network under the default netmask
This Is Easy
(If you grasp the binary)
We can divide these 8 bits whichever way
best fits the number of networks and
hosts per network that we require.
If, for example we choose to split it down
the middle, 4 and 4, we end up with 14
(2^4 = 16 – 2 = 14) networks and 14
hosts per network.
Breaking It Down
(Enumerating the bits)
So, we have 4 bits for the network portion, Let us
enumerate all of the possible binary values
using the 4 most significant bits of an 8 bit
number:
0000
0100
1000
1100
0001
0101
1001
1101
0010
0110
1010
1110
0011
0111
1011
1111
Enumerating Subnets
(What are the possible subnets)
So, for each possible value for the 4 bits, we
have a separate subnet:
208.98.1.0
(0000 0000)
208.98.1.16
(0001 0000)
208.98.1.32
(0010 0000)
208.98.1.48
(0011 0000)
…
208.98.1.240
(1111 0000)
Enumerating Hosts
(What are the usable IP addresses)
In the subnet 208.98.1.32 netmask
255.255.255.240 we have 14 usable ips:
208.98.1.33
(0010 0001)
208.98.1.34
(0010 0010)
208.98.1.35
(0010 0011)
…
208.98.1.62
(0010 1110)
.63 is the broadcast address (0010 1111)
Network Boundaries
(Are you my neighbour?)
To calculate if two hosts are in the same
network, you need to know their subnet
mask. i.e. netmask 255.255.255.240
208.98.1.60
11010000.01100010.00000001.00111100
208.98.1.66
11010000.01100010.00000001.01000010
So, we can see these two hosts are not
in the same network