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running AppleTalk, TCP/IP, and IPX, must have three network layer addresses for each interface. The
router therefore has nine network layer addresses.
*Keypoints:Know that the 2 parts to an IPX address are the 1) network number and 2) MAC address (host num-ber).TCP/IPIP Addressing Fundamentals
A host or node is a computer or device on a TCP/IP network. Every TCP/IP host is uniquely identified
by its IP address. An IP address consists of a network ID and a host ID. If two different hosts belong
to the same network, they have the same network ID. The two hosts will have different host ID's and
can communicate with each other locally without going through a router. If two hosts have different
network ID's, they belong to different segments on the network. They must communicate with each
other remotely through a router or default gateway.
An IP address consists of 32 binary bits, where each bit is either a 0 or 1. We write the 32 bits into four
8-bit numbers (octets) separated by a periods.
For Example: 11000001 . 00001010 . 00011110 . 00000010 (IP address in binary form)
To convert the IP address from binary to decimal form, we convert each of the four 8-bit numbers in
each octet according to the following table:
Decimal Value
128
64
32
16
8
4
2
1
Octet Value
x
x
x
x
x
x
x
x
So the first octet in the above binary number would be translated as:
Decimal Value
128
64
32
16
8
4
2
1
Octet Value
1
1
0
0
0
0
0
1
Everywhere a 1 appears in the table, the decimal value in that column is added to determine the decimal
value of the entire octet.
or 128 + 64 + 1 = 193
Using the same table to translate the other three octets would give us the following result.
00001010 = 8 + 2 = 10
00011110 = 16 + 8 + 4 + 2 = 30
00000010 = 2
So in decimal form, the above IP address is: 193 . 10 . 30 . 2
Address Classes
An IP address consists of two parts, one identifying the network and one identifying the host. The Class
of the address determines which part is the network address and which part is the host address.
There are 5 different address classes. Classes can be distinguished by the decimal notation of the very
first octet. The following Address Class table illustrates how you can determine to which class and ad-
dress belongs.