Class A Range

Hey can anyone clarify the Class A Range...

PacketLife and Wikipedia list the range as 0-127 (in the first octet), but Odom's ICND1 Book says Class A begins with 1-126.

Todd Lammles CCNA book also says it is between 0-127 inclusive.

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Comments

kryolla

Take into account the private addresses and 169 and 127, etc
class A
00000000
01111111

class B
10000000
10111111

class C
11000000
11011111

class D
11100000
11101111

dshay25

127 range = loopback

typesh

dshay25 wrote: »

127 range = loopback

But is 127 (loopback) considered part of Class A?

I find documentation that says 127 is included in Class A (Wiki/Lammle/Packetlife), but then I come across documentation that says Class A is between 1-126 inclusive.

Which is correct?

stuh84

typesh wrote: »

But is 127 (loopback) considered part of Class A?

I find documentation that says 127 is included in Class A (Wiki/Lammle/Packetlife), but then I come across documentation that says Class A is between 1-126 inclusive.

Which is correct?

1-126 is USABLE assignable Class A, however 0 and 127 are still classed as Class A, you just can't assign them to anything (except 127 which is loopback as mentioned)

dshay25

typesh wrote: »

But is 127 (loopback) considered part of Class A?

I find documentation that says 127 is included in Class A (Wiki/Lammle/Packetlife), but then I come across documentation that says Class A is between 1-126 inclusive.

Which is correct?

Yes, 127 is class A but not usable.

Class A = 00000000-01111111
(0-127)

thenjduke

0-127 is class A
0-126 are usable IP range in Class A
so technically it is.
127 is loopback.

bubble2005

The Cisco's accepted Class A ranges are 1-126. 127 is considered a loopback address, an address by itself and is not considered to be USED in Class A. Beware of questions like that!

billscott92787

Usable range is:

1 - 126

0 is reserved
127 is reserved -> loopback

GT-Rob

Everyone is correct here. Its just a matter of how the question is posed.

127.0.0.1 is an address in which class?

a
b
c
d

If the question was, what is a usable class a address?

192.168.0.0
10.5.5.5
127.0.0.1
256.256.1.1

Those are the types of questions you need to be able to understand and answer.

typesh

Got it. Thanks!

Haruna Umar Adoga

the class A ip range is 0-127, but only 1-126 is the valid range that's been used for host assignments and
127.0.0.1 is reserved for loopback testing i.e to test your local TCP/IP protocol stack, if the command C:>ping 127.0.0.1 on your PC fails, it means you have a problem with your TCP/IP stack on the pc.
maybe you should try it now !

amtt81

I have trouble with the concept that the valid class A range is 1-126 however the first usable address in the Class A network is 10.0.0.1 ---

Where does the 10 come from? Why isnt the first address 1.0.0.1?

Also why isnt the Class B address 128.0.0.1 instead of 172.16.0.1?

I know I can just memorize the address ranges but my brain wont let this go.

I have also wanted to ask - why do we subtract from 256 when the highest possible address is 255 (11111111)

Jefrey

amtt81 wrote: »

I have trouble with the concept that the valid class A range is 1-126 however the first usable address in the Class A network is 10.0.0.1 ---

Where does the 10 come from? Why isnt the first address 1.0.0.1?

Also why isnt the Class B address 128.0.0.1 instead of 172.16.0.1?

I know I can just memorize the address ranges but my brain wont let this go.

I have also wanted to ask - why do we subtract from 256 when the highest possible address is 255 (11111111)

Interesting question hope that someone knows the answer, but i couldn't find nothing about it from IANA...on a side maybe those ranges where already taken or reserved for something else who knows...

Btw we subtract from 256 cause the lowest possible address is 0 (00000000) not 1

0-255=256

networker050184

amtt81 wrote: »

I have trouble with the concept that the valid class A range is 1-126 however the first usable address in the Class A network is 10.0.0.1 ---

Where does the 10 come from? Why isnt the first address 1.0.0.1?

Also why isnt the Class B address 128.0.0.1 instead of 172.16.0.1?

I know I can just memorize the address ranges but my brain wont let this go.

I have also wanted to ask - why do we subtract from 256 when the highest possible address is 255 (11111111)

I think there may be some confusion here. 10.0.0.0 and 172.16.0.0 addresses are private addresses. There are also reserved addresses for other uses.

kryolla

amtt81 wrote: »

I have trouble with the concept that the valid class A range is 1-126 however the first usable address in the Class A network is 10.0.0.1 ---

Where does the 10 come from? Why isnt the first address 1.0.0.1?

Also why isnt the Class B address 128.0.0.1 instead of 172.16.0.1?

I know I can just memorize the address ranges but my brain wont let this go.

I have also wanted to ask - why do we subtract from 256 when the highest possible address is 255 (11111111)

you are correct on the first address for each class. You can use whatever IP range you want to put it CAN'T leave your network, it has to be translated into an ip address given to you by the provider. If you use the private address your provider is blocking it in incase you let it slip out.

amtt81

Well, thank you for the responses. I realize that 10.0.0.0 and 172.16.0.0 are reserved, but even though they are reserved they define the beginning of each class range right? So I just dont understand where the class A 1-126 and class B 128-191 come from if you then say the first address of A (although reserved) is 10.0.0.1 not 1.0.0.1 ---- and the first address of B (although reserved) is 172.16.0.1 and not 128.0.0.1 - i mean is 128.0.0.1 a valid address anywhere?

kryolla

you are correct on the first address for each class i.e 1.0.0.1 for class A

Jefrey

lol funny thread were just spinning around the circle....

Ok to clear this up

Private ip doesn't define beginning of class range, and well i hoped someone could provide better answer but lets start from this...
Private ip addresses where not predicted on the beginning of the internet, i mean nobody thought they were necessary...but after some time people calculated that address space is not going to be big enough and it will reach the end soon, so IANA and big ISPs just had to stop giving blocks of ip addresses so easily to everyone who asks and they had to do something about the addressing space thats becoming narrow....
They probably had few ideas but few show up first...either to invent new addressing scheme(like they did with IPV6 128 bits address eventually) or to find some alternative solution...and the private ip range is born...on the end we had result where companies could have solid network of 500 hosts communicating with each other through lan and when is necessary go on the internet with the help of NAT(read about it).
Now if i understood your question it was about why the private ip of class A and B doesn't define the starting of some range like it does for the class C where the first address is private...but it isn't actually its not even begging of the class C cause class C starts with 192.0.0.0 and private ip range under class C starts with 192.168.0.0 /16...so we have a bunch of addresses before we even come to private address range of class C addresses.
Why i can't tell for sure i really don't know but i tried to give logical explanation why private address ranges aren't the first networks in the class and as i said i think it was because private ranges where not even planed to exist while something else might have...so i thought they could be easily already taken or reserved for something else, what i don't know but u can maybe check IANA for reserved ip ranges and maybe you can post here what u got so we could know for sure.

Cheers

networker050184

Take a look here a high level view of IP address assignments.

I don't know where you are getting that 10.0.0.0 is the first usable Class A address space. There are lower number IP addresses assigned and active on the internet.

dhafar

I'll explain it it start from 0 to 127 class Aso 0 ==== Network 127===Broadcast it will become 126 because remove zero and 127 like this Host= IP - 2

Jon_Cisco

kryolla wrote: »

class A
00000000
01111111

class B
10000000
10111111

class C
11000000
11011111

class D
11100000
11101111

This is the key point for classes. Once you understand the binary the ranges make more sense.

Don't confuse the private addresses they do not define the classes.

davenull

I'm sure the information here is still valid and useful, but this thread is over 5 years old ... just saying