Hi,
RFC 943 is pretty old...
Just think about classfull routing at those dates, and classless routing and
VLSM now...
More of this, RFC 1783 (if I remember) obsoltes RFC 943, and is also obsolte.
The right assigned numbers are on www.iana.org home page.
Hope this helps,
jean-marc
On 18-Dec-00 Ole Drews Jensen wrote:
> I thought I knew it by heard now, but when I had to prove a point to
> someone, I grapped some of my books, and they all have different
> explanations. I therefore jumped to IETF's homepage and started surfing
> their RFC's. BUT...
>
> On RFC 943 (Assigned Numbers) it says on page 1:
>
> Class A has 7 bit network number which allows 128 (2^7) networks.
> Class B has 14 bit network number which allows 16384 (2^14) networks
> Class C has 21 bit network number which allows 2097152 (2^21) networks
>
> This looks right, because the MSB is 0 in a Class A, thus the 7 bits. It is
> only 127 networks though, since 127.x.x.x is reserved. That is also
> explained later in the RFC. The MSB in Class B is 10, thus the 14 bits. And
> finally, the MSB in Class C is 110, thus the 21 bits.
>
> On page page 10 however, it says that the maximum allowed networks are:
>
> Class A : (2^7 - 2) 126
> Class B : (2^14 - 2) 16382
> Class C : (2^21 - 2) 2097150
>
> It now looks like it follows the same rule as host calculations, where you
> cannot use all 0's or all 1's.
>
> I have looked through all my books (I have a lot) and they all have slightly
> different opinions about this.
>
> What is the right answer?
>
> Class A is from 0.x.x.x to 126.x.x.x OR 1.x.x.x to 126.x.x.x ?
>
> Class B is from 128.0.x.x to 191.255.x.x OR 128.1.x.x to 191.254.x.x ?
>
> Class C is from 192.0.0.x to 223.255.255.x OR 192.0.1.x to 223.255.254.x ?
>
> Regarding SUBNET's, they all have the same explanation, but here it is
> anyway. If you use 192.168.1.0/28, you have 4 bits for the subnet and 4 bits
> for the hosts, which give you 2^4 - 2 = 14 subnets with 14 hosts each. I am
> pretty sure that that is the right explanation.
>
> Thanks for any comments on this,
>
> Ole
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Ole Drews Jensen
> Systems Network Manager
> CCNA, MCSE, MCP+I
> RWR Enterprises, Inc.
> [EMAIL PROTECTED]
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----------------------------------
E-Mail: Jean-Marc Gilbert <[EMAIL PROTECTED]>
Date: 18-Dec-00
Time: 19:05:36
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