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Chapter 3

IP Addressing

router might be able to speed a packet on its way after reading only the first
bit of its address. This is where the address schemes define the difference
between a Class A, a Class B, and a Class C address.

Some IP addresses are reserved for special purposes, and network admin-

istrators shouldn't assign them to nodes. Table 3.2 lists the members of this
exclusive little club and explains why they're included in it.

We will now take a look at the different network address classes:

Class A addresses

Class B addresses

Class C addresses

T A B L E 3 . 2

Reserved IP Addresses

Address

Function

Network address of all zeros

Interpreted to mean "this network
or segment."

Network address of all ones

Interpreted to mean "all networks."

Network 127

Reserved for loopback tests. Desig-
nates the local node and allows that
node to send a test packet to itself
without generating network traffic.

Node address of all zeros

Interpreted to mean "this network."

Node address of all ones

Interpreted to mean "all nodes" on
the specified network; for example,
128.2.255.255 means "all nodes"
on network 128.2 (Class B address).

Entire IP address set to all zeros

Used by Cisco routers to designate

the default route.

Entire IP address set to all ones
(same as 255.255.255.255)

Broadcast to all nodes on the cur-
rent network; sometimes called an
"all ones broadcast."

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