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What Ip addresses do we actually use and what we do not ?
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Ranges 127.x.x.x are reserved for the loopback or localhost, for example, 127.0.0.1 is the loopback address.

Range 255.255.255.255 broadcasts to all hosts on the local network.

192.168.1.0               0 is the automatically assigned network address.

192.168.1.1               1 is the commonly used address used as the gateway.
192.168.1.2               2 is also a commonly used address used for a gateway.
192.168.1.3 - 254      Addresses beyond 3 are assigned to computers and devices on the network.
192.168.1.255          255 is automatically assigned on most networks as the broadcast address.

First Ip address in any class network which is having a valid no in n/w id and all 0's in host id part indicates the network id of entire network.

Last Ip address of any class is used as Directed Broadcast Address.Means if a Host in some n/w wants to send a message to all the other host in some other n/w.For exp 

N/w id for N/w A is Let say 20.0.0.0 which is having a Host Let say 20.1.2.3 wants to send a message to all the hosts in n/w having n/w id as 25.0.0.0 .

by Boss (45.4k points)
edited by
+2 votes

 For each network ID, two host IDs cannot be used: the host ID with all zeroes and the ID with all ones. These are addresses with "special meanings".

Special Network ID and Host ID Address Patterns

Special IP addresses are constructed by replacing the normal network ID or host ID (or both) in an IP address with one of two special patterns. The two patterns are:

  • All Zeroes: When the network ID or host ID bits are replaced by a set of all zeroes, the special meaning is the equivalent of the pronoun “this”, referring to whatever was replaced. It can also be interpreted as “the default” or “the current”. So for example, if we replace the network ID with all zeroes but leave the host ID alone, the resulting address means “the device with the host ID given, on this network”. Or alternatively, “the device with the host ID specified, on the default network or the current network”. 
     
  • All Ones: When the network ID or host ID bits are replaced by a set of all ones, this has the special meaning of “all”. So replacing the host ID with all ones means the IP address refers to all hosts on the network. This is generally used as a broadcast address for sending a message to “everyone”.
by Boss (41.2k points)
+1 vote

Okay so Classfull addressing is a technique which was used earlier to solve the distribution of IP address.

How this works!!

we all know that a ip address is of 32 bits and for the sake of simplicity we have divide it into 4 octets each of 8 bits

so we have  4 like this where we can fill either 0 or 1 _ _ _ _ _ _ _ _

now understand this concept assume you have 2 bits _ _

you can have 4 diff. permutations with 0 and 1 i.e. 00,01,11,10

so if you fix a bit at a position to extreme right , we can divide it into 2 possible configuration i.e if we fix first bit as 1 then we can have 10 or 11..

now if we have 3 bits _ _ _, we have 8 possible permutations, then if we fix the same right bit again as 1, then

we can have 100,101,110,111 as our posiiblities

did you see the pattren 

our total space for 2 bits was 22

and after fixing one bit we are remained with 22/21(because we have fixed one bit) = 2

and in case of 3, after fixing one bit , we are remained with 23/21(again same reason) = 4

i.e when we divide 32 bits by fixing one bit, we are remained with 232/21  = 231

till now i hope you understood

so what we do in classfull addressing is we divide 32 bits first in 2 parts by fixing one bit as 0 ( 0 _ _  _ _ _ _ _ _)

and this gives us 2 parts (range 0-127 fo 1st part where 0 is fixed and 128-255 part where 1 is fixed as total sample space was 256 for 8 bits in first octat) { 

we call first one (range 0 to 127) as class A  {{ 0 _ _ _ _ _ _ _  00000000 to 01111111) }}

and then we further divide by fixing second most right as 0(which gives us the range(127-191) and (192-255)

this (127-191) is called as class B {{ 10 _ _ _ _ _ _   10000000 to 10111111}}

and we further divide(192-255)t into 2 parts by fixing 3rd bit as 0

in 192-223 adn 224-255

an we call 192-223 as class C {{ 110 _ _ _ _ _   11000000 to 11011111}}

and then for class D we further divide 223-255 range in 2 parts by fixing 4th right bit

224-239 and 240-255

and we call 224-239 as class D {{ 1110_ _ _ _ 11100000 to 11101111}}

whereas 240-255 is class E {{ 1111 _ _ _ _  11110000 to 11111111}}

note : i am talking about the first octet here. and octet refers to grp of 8 bits. feel free to ask ques.

by Active (2.6k points)
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