Archived from groups: microsoft.public.win98.gen_discussion (
More info?)
"Eugene F." <pm771.am@gmail.com> wrote in message
news:1112622102.556032.64880@o13g2000cwo.googlegroups.com...
> Hugh,
>
> Thank you very much for the reply.
>
> <<< Default subnet masks are based on the IP address classes. >>>
>
> What does it mean exactly? Sorry, but networking is not my cup of tea.
>
this might explain it for you
An IP address is composed of 32 bits. These 32 bits are divided into 4
octets of 8 bits each. You may have seen an IP address represented like
this: 172.68.15.24. We must remember, however, that the computer understands
this number only in binary, so we must often deal with them in binary. Many
people are intimidated by this initially, but soon find that it is not
difficult. If you do not allow yourself to be flustered, you can master this
topic.
IP addresses are assigned to orginazations in blocks. Each block belongs to
one of three classes: class A, class B, or class C. You can tell what class
an IP address is by the value in its first octet.
Class A 1-126
Class B 128-191
Class C 192 -->
An IP address consists of two fields. The first field identifies the
network, and the second field identifies the node on the network. Which bits
of the address are in the network field and which bits are in the host field
is determined by the subnet mask.
When a class A IP license is granted, you are assigned something like this:
99.0.0.0. Only the value of the bits in the first octet are assigned. This
means you are free to assign any values you wish in the second, third and
fourth octets.
The defualt subnet mask for a class A network is 255.0.0.0. High bits, ones,
indicate the bits that are part of the network field of the IP address. The
default subnet mask does not create subnets. Therefor, a class A network
with the default subnet mask is one network. The three octets that are
unassigned and unmasked are part of the host field of the address. There is
a total of 24 bits in those three octets. Each bit can be in one of two
states. Therefor, 2^24 is the number of host addresses that can be assigned
on that network, almost. Two addresses are reserved on every network,
x.x.x.0 and x.x.x.255. So the total number of hosts possible on this network
is 2^24. 2^24-2=16,777,214 hosts for a class A IP network.
When a class B license is granted, the first two octets are assigned. For
example, 172.198.x.x. The default subnet mask for a class B is 255.255.0.0.
One network, two octets free, 16 bits for the host address field.
2^16-2=65,534 possible host addresses on a class B IP network.
When a class C license is granted, the first three octets are assigned, for
example: 193.52.16.0. The default subnet mask for a class C is
255.255.255.0. Once octet makes up the host address field. 2^8-2=254 host
addresses possible on a class C network.
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