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PPENDIX
B: IP A
DDRESSING
can be, but does not have to be, the same as the netmask for any other
supernet.
As in subnetting, a netmask creates a division between the network
portion of an address and the host portion of an address. However, since
the network you are defining is larger than a Class C network, the
division you are creating is not in the fourth octet of the address. For this
example, we'll be creating supernets composed of fewer than 254 Class
C networks. So, their netmasks will actually be splitting up the third octet
in their IP addresses.
The number of zero bits in the third octet will actually dictate the number
of Class C networks in the supernet. Each zero bit makes the supernet
twice as large. So, a supernet composed of 8 Class C networks would
actually have 3 zeroes (8 = 23).
This would seem very limited since it restricts you to using groups that
nicely fit into a power of 2 (1, 2, 4, 8, 16...). However,
inconveniently-sized supernets can be accommodated because of a
simple fact: a netmask with more 1 bits will override a netmask with
fewer 1 bits.
This allows a smaller supernet to share the address space of a larger
supernet. If, for example, you had a supernet of size 6 and a supernet of
size 2, you could assign the larger supernet an 8 network address space
and assign the smaller supernet the portion of that address space that the
larger supernet was not using. Because the smaller supernet's netmask
has more 1 bits, packets whose address was part of its address space
would be routed to the smaller supernet even though the address is also
part of the address space dictated by the larger supernet's netmask.
You must select a range of addresses for each supernet. The range of
addresses in a supernet must fit exactly into a space that can be described
by its netmask. This means that the zero bits in the netmask must also
appear in the first address of the supernet block. For this to be true, the
third octet in the address must be an even multiple of the same power of
2 used to form the netmask. For example, if you had created a block of 8
networks, the third octet in the first address will be an even multiple of 8.
Supernetting and the
OfficeConnect
Remote 840
In order to define a supernet on the OfficeConnect Remote 840, you
must add the network address and its netmask. You have two options
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