Intel ER8100STUS - Express 8100 Router, Reference Manual

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Reference.bok : Chapter08 50 Wed Apr 22 10:58:08 1998
50
IP Concept
IP Routing
Characteristics
An IP subnet functions as an independent network. To a remote network it ap-
pears to be a single discrete network.
How to create
subnets
To create a subnet you must impose a hierarchy on host addresses which allows
for multiple subnets to exist within a single class A, B or C network. It is the high
order bits of the hosts part that specify the subnet. Derive the IP network by
ANDing the IP address with the subnet mask:
An example of the network part looks like this:
Decimal Notation:
16.1.0.1
AND
255.255.192.0
=
16.1.0.0
Hexadecimal Notation:
0x10010001
AND
0xffffc000
=
0x10010000
Subnet masks A subnet mask specifies which part of the host’s address is used to define the sub-
net. It is a 32-bit IP address written in dotted-decimal notation with all ones (bi-
nary) in the network and subnet part of the IP address.
Note
When a subnet mask is used on an IP address, the resulting host part of
the address must not end in zero or 255.
1 2 3 4
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
Class B address (subnet mask 255.255.0.0)
Network part Local host part
Class B subnet (subnet mask for example 255.255.192.0)
Network part Local host part