Ok, this explains sub net addressing which is useful if you run a scanner, a firewall, a router or anything else that is bound to IP sub net addressing. Note that this only describes IPv 4 sub nets. Reading binary values Normally, you read binary numbers byte wise (8 bit wise).
Start at the last bit, bit 0. If it is 1, add 2^0 to your number, else add 0. Then the next bit, bit 1, If it is 1, add 2^1 (2) to your number, If bit 3 is 1 add 2^2 (4) to your number, if bit 4 is 1 add 2^3 (8) to your number…
if bit 8 is 1 add 2^7 (128) to your number. You see, the base is always 2 because it can be either 0 or 1. Example 1: 10100100 = 2^7+0+2^5+0+0+0+2^2+0+0 = 164 Example 2: 11111111 = 2^7+2^6+2^5+2^4+2^3+2^2+2^1+2^0 = 255 Thats it! Now to sub net addressing. When you state a host including a sub net (example: n map), you do it like this: 1.
2. 3. 4/24, where /24 is the sub net. Lets have a look at what this means: an IP address is a 32 bit address. It is divided into 4 bytes (each 8 bits meaning they can be 0 to 255) in general notation: 00000001 00000010 00000011 00000100 = ‘1.
2. 3. 4’now, IP uses one part of this address to specify which Net it is on. Most of the time, this is a physical Net like an ethernet LAN that is linked to the internet. Nets that link to the internet get dedicated IPs for each of their hosts from the IANA. org.
/24 means that the first 24 bits are the Net address and the remaining 8 bits are the Host address. This looks like this: Net: 000000010000001000000011 Host: 00000100 Meaning, we are on the net 1. 2. 3. 0 (0 used as a wildcard here) and on the host 4 of 256.
The Term Paper on The Hole In The Net
... net to help him get back up -- how can you apply for a job when you don't have a phone number, address ... that there is incessant violence, and a whole host of other complaints, but they can all be ... historically useful tool for restoring trade imbalances. They add money to the federal budget while encouraging Americans ... But she, like so many, slipped a little bit and there was nothing to catch her.' Hello ...
SUBNET MASK: In this case, the sub net mask would be 255. 255. 255. 0.
A sub net mask is created simply by filling all NET address bits with 1 and the HOST bits with 0. (11111111 = 255).
There are 4 ‘Classes’ on the Internet, which are the standard Subnets. Class A: ‘0’ + 7 net bits + 24 host bits, hosts 0.
0. 0. 0 to 126. 255. 255.
255 Net IDs: 0 0000000 to 0 1111111 (which is 127 = > 127. 0. 0. 0 reserved for local loop back) Class B: ’10’ + 14 net bits + 14 host bits, hosts 128.
1. 0. 0 to 191. 254. 0.
0 Net IDs: 10 00000000000000 to 10 11111111111111 Class C: ‘110’ + 21 net bits ( = 24) + 8 host bits, hosts 192. 0. 1. 0 to 223.
255. 254 Class D: ‘1110’ + 28 bits for multi cast addresses (reserved), hosts 224. 0. 0. 0 to 239.
255. 255. 254 Class E: ‘1111’ + 28 bits for unused addresses (‘martians’), hosts 240. 0. 0. 1 to 255.
255. 255. 254 0. 0.
0. 0/255. 255. 255.
255 = broadcast packets (0 and 255 are used for ‘all hosts’) One more example: If you address a sub net with the mask: 255. 255. 192. 0 (which is 111111111111111111 00000000000000), you can specify a sub net with: 190.
136. 64. 0/18 (18 net id bits) which would address 190. 136. 64. 0 to 190.
136. 127. 255 or: 101111101000100001 00000000000000 to 101111101000100001 11111111111111. Other nets on that sub net would be: Subnet mask 190. 136. 0.
0/18 Net ID Host ID 190. 136. 0. 0 1011111010001000 00 00000000000000 190.
136. 64. 0 1011111010001000 01 00000000000000 190. 136.
128. 0 1011111010001000 10 00000000000000 190. 136. 192. 0 1011111010001000 11 00000000000000 Note: The first and the last sub net could not be used because Net ID 00 and 11 would be interpreted as broadcasts (like broadcast ids 0 (00000000) and 255 (11111111) ).
For further info check the RFC 791 (web)..
