TCP/IP Addressing & Subnetting
Hey guys, found this on the net and thought it could be of some intrest to you Internet Buffs out there :p. Now I'm hoping you know what this is about, obviously by the name of the thread...
Every IP address can be broken down into 2 parts, the Network ID(netid) and the Host ID (hostid). All hosts on the same network must have the same netid. Each of these hosts must have a hostid that is unique in relation to the netid. IP addresses are divided into 8 octets with each having a maximum value of 255. We view IP addresses in decimal notation such as xxx.xxx.xxx.xxx, but it is actually utilized as binary data so one must be able to convert addresses back and forth.
CONVERTING IP ADDRESSES BACK AND FORTH
Code:
Decimal Binary
128-------------10000000
64---------------01000000
32---------------00100000
16---------------00010000
8-----------------00001000
4-----------------00000100
2-----------------00000010
1-----------------00000001
When converting binary data to decimal, a "0" is equal to 0. "1" is equal to the number that corresponds to the field it is in. For example, the number 213 would be 11010101 in binary notation. This is calculated as follows:
128+64+0+16+0+4+0+1=213.
Remember that this only represents 1 octet of 8 bits, while a full IP address is 32 bits made up of 4 octets. This being true, the IP address 213.128.68.130 would look like 11010101 10000000 01000100 10000010. If you understand this then you are a geek and all of your friends will laugh at you. Believe me - I know! :p
CLASSES
Code:
Class Range
A-------------10000000
B-------------01000000
C-------------00100000
IP addresses can be class A, B or C.
- Class A addresses are for networks with a large number of hosts. The first octet is the netid and the 3 remaining octets are the hostid.
- Class B addresses are used in medium to large networks with the first 2 octets making up the netid and the remaining 2 are the hostid.
- A class C is for smaller networks with the first 3 octets making up the netid and the last octet comprising the hostid.
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SUBNETTING
A subnet mask blocks out a portion of an IP address and is used to differentiate between the hostid and netid. The default subnet masks are as follows:
Code:
Class Default Subnet # Of Subnets # Of Hosts Per Subnet
Class A------255.0.0.0---------------126-------------------16,777,214
Class B------255.255.0.0------------16,384------------------65,534
Class C------255.255.255.0---------2,097,152---------------254
In these cases, the part of the IP address blocked out by 255 is the netid.
The table above shows the default subnet masks. What subnet mask do you use when you want more that 1 subnet? Lets say, for example, that you want 8 subnets and will be using a class C address. The first thing you want to do is convert the number of subnets into binary, so our example would be 00001000. Moving from left to right, drop all zeros until you get to the first "1". For us that would leave 1000. It takes 4 bits to make 8 in binary so we add a "1" to the first 4 high order bits of the 4th octet of the subnet mask (since it is class C) as follows:
11111111.11111111.11111111.11110000 = 255.255.255.240.
There is our subnet mask. Lets try another one...Lets say that you are the network administrator for a chain of dry cleaning stores in New York and you have stores in 20 different neighborhoods and you want to have a separate subnet on your network for each store. It will be a class B network. First, we convert 20 to binary - 00010100. We drop all zeros before the first "1" and that leaves 10100. It takes 5 bits to make 20 in binary so we add a "1" to the first 5 high order bits which gives:
11111111.11111111.11111000.00000000 = 255.255.248.0.
The following table shows a comparison between the different subnet masks.
Code:
Mask # of Subnets ClassA Hosts ClassB Hosts ClassC Hosts
192------------2-----------------------4,194,302-----------16,382----------------62
224------------6-----------------------2,097,150-----------8,190------------------30
240------------14----------------------1,048,574----------4,094------------------14
248------------30----------------------524,286-------------2,046------------------6
252------------62----------------------262,142-------------1,022------------------2
254------------126--------------------131,070--------------510---------------------Invalid
255------------254--------------------65,534----------------254---------------------Invalid
thanks webc, but i have some questions:
I understood all that, but now I have some questions:
In the first example
Lets say, for example, that you want 8 subnets and will be using a class C address.
You get 255.255.255.240 as the subnet mask...
so now we have 8 subnets, ok now waht about hosts? How many hosts can we have per subnet...
can u give an example of the whole 32 bit ip address and subnet for each of the 8 subnets?
I just want an example of how they look, to see if my calculations were correct...
thanks for the info WebCarnage, this could be of real help in my work.
ok following your first exampl..another question
if u want to have 8 subnets, you see that it would take 4 bits to make 8 in binary, so to get 8 subnets u would have 255.255.255.240...
but then again, to make 14 in binary it takes 4 bits....to make 10 or even 9 it takes 4 bits...so the 255.255.255.240 can be used to make 8 subnets or 14 subnets or 10 or 9?
clarify please!!!
