Learn how to Subnet. Free "crash course" to make this simple. Some examples.
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Subnetting is fun. It is fairly easy but requires a lot of math. The act of subnetting is to be able to add networks from a single IP address range to efficiently add more clients. Most classful network ranges given will have a lot of wasted IP addresses. For example, you have a home network, you only have say 5 devices, including computers, that need IP addresses. The range given on most home routers are set for 192.168.1.0/24. This network range would allow you to have 254 clients connected to the network. This will be wasting 249 addresses. Subnetting will break down the network range to what will more closely fit your needs to optimize your given IP address range. For the example the address should be subnetted to 192.168.1.8/29. This will allow up to 7 clients connected to the network per subnet. I know I am getting a little ahead of myself, so lets slow this down and give you some useful information.
Before we continue, I should go over IP address ranges and valid IP addresses and invalid IP addresses.
IP's addresses
127.0.0.1 is a loopback IP address >> Invalid
169.x.x.x is an IP address given by the APIPA >> Invalid. This IP address is automatically given to client computers that can't communicate with a DHCP server and doesn't have a static IP address.
Broadcast addresses such as 192.168.1.255 is invalid because this is a broadcast address for this range.
Unicast addresses such as 192.168.1.0 is invalid because this is the network range.
Ranges
There are 3 classful IP address ranges Class A, Class B, and Class C.
Class A
0.0.0.0 >> 127.255.255.255 with subnet mask of 255.0.0.0
Class B
128.0.0.0 >> 191.255.255.255 with subnet mask of 255.255.0.0
Class C
192.0.0.0 >> 223.255.255.255 with subnet mask of 255.255.255.0
Most common home networks use a DHCP on their router with the default IP address range of 192.168.x.x mask 255.255.255.0
Because this range uses the least amount of IP addresses, can have up to 254 clients.
Breaking down the subnet mask
The subnet mask is made up of 32 bits. We all only see the subnet mask as numerical digits but it actually is
00000000.00000000.00000000.00000000 in binary. Binary counts from right to left. The 0 means that the bit is turned off. The 1 means that the bit is turned on.
So the subnet mask of 255.255.255.0 is 11111111.11111111.11111111.00000000 in binary. If you count all the 1's in the mask, then you will get 24 which will also be called the CIDR bit.
The following is to show you the setup of subnet masks again using the 192.168.1.0/24 address
255 . 255 . 255 . 0
network.network.network.node
CIDR
CIDR is the amount of bits used in the subnet mask used to make the IP address range. Sample of using 192.168.1.15/24. This means that the IP address shown is using 24 bits in the subnet mask.
Binary
Binary counts as:
0 >> 00000000
1 >> 00000001
2 >> 00000010
4 >> 00000100
8 >> 00001000
16 >> 00010000
32 >> 00100000
64 >> 01000000
128 >> 10000000
So to get the subnet mask for 255.0.0.0 with binary 11111111.00000000.00000000.00000000. We just take all the values from the chart above and add then up
1+2+4+8+16+32+128=255
Understand the fundamentals?
Now to get to the juicy stuff.
Classless Subnets
When we subnet a classful address to gain more clients, it will change its classful address to what we determine. Now if you are taking a Cisco class or studying for the CCNA exam, this will be on both. The first example I will show you is to setup a simple WAN connection for two routers to help improve IP addressing schemes.
Say you have to routers on a network. The link will only have two IP addresses that will be used so you might think a Class C addressing scheme will be the best to use. But, you will still be wasting 252 addresses. That is alot of IP's that you could use else where. So to improve this scheme we will subnet the addresses to only using what is needed for the WAN link.
We will use the 192.168.1.0/24 address again to show you the basics.
Binary reads the subnet mask as:
11111111.11111111.11111111.00000000
We will be "borrowing" bits from the client side of the network address (the client side is represented by "0").
The best formula is used is from my CCNA class I took.
To calculate your subnets use:
2 exp x - 2 = number of subnets. X being the bits borrowed from the clients side ("1's")
We subtract 2 because the first and last network can't be used
To calculate your node addresses use:
2 exp y - 2 = number of client addresses. Y is the unused bits ("0's")
We subtract 2 because the first and last client address can't be used. They are broadcast and unicast addresses.
So if we only want 2 host addresses. You will borrow a few bits from the client or node. Like:
255 . 255 . 255 . 252
111111111.11111111.11111111.11111100
To get 252 for the subnet mask you just add up all the binary bits used.
128+64+32+16+8+4=252
This mask will give 62 valid networks using the formula:
2 exp 6 - 2 = 62
The amount of available client addresses will be 2 using the formula:
2 exp 2 -2 = 2
Now if you subtract 252 from 256, which 256 is a constant, then you will get 4. This tells you the valid subnet ranges. Again, they do not use the first and last subnet so the valid networks are:
4,8,12, etc., up to 240,244, and 248. 248 is the last valid network.
Addresses in the first network would be:
192.168.1.4/30
192.168.1.4 - not valid, unicast
192.168.1.5 - valid
192.168.1.6 - valid
192.168.1.7 - not valid, broadcast
That is alot of IP addresses you can use to stop minimize collisions and broadcasts on a network.
Having fun yet?
Click on the link if you want to learn more about networking concepts and get some ebooks to learn from.
http://it-helper.net23.net
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