Actually, it goes like this:
0xxx Class A Decimal range: 0 - 127
10xx Class B Decimal range: 128 - 191
110x Class C Decimal range: 192 - 223
1110 Class D Decimal range: 224 - 239
0xxx Class E Decimal range: 240 - 255
Notice that the position of the "zero" bit keeps walking to the
right as you go down the classes. Of course, this is only important
in the classroom and for Cisco exams since in the "real world" classful
addressing is a thing of the past! And as Brian stated, the mask
has nothing to do with the class except in the context of the "default
mask" which in classful addressing identifies the network portion of the
address in an un-subnetted network.
Perhaps someday, Cisco will let us teach VLSM in the CCNA classes.
:)
Tom Lisa, Instructor
Cisco Networking Academy
Community College of Southern Nevada
Brian wrote:
On Fri, 6 Oct 2000, Oscar Rau wrote:
> I am trying to determine the IP addresses assigned by a local ISP.
> The address pool comes from a Class A network with a 27 bit subnet
mask.
>
> Is it subnet mask used only to determine the number of IP addresses
in a subnet,
> regardless of the network class?
subnet mask has nothing to do with determining the "class" of a
network. The first 3 bits of the address will tell you the class:
000 Class A
100 Class B
110 Class C
111 Class D
Brian
> --
>
> Oscar Rau
> [EMAIL PROTECTED]
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Brian Feeny, CCNP, CCDP [EMAIL PROTECTED]
Network Administrator
ShreveNet Inc. (ASN 11881)
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