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Chapter 3

Internet Protocols

Network Address Ranges: Classes D and E

The addresses between 224 and 255 are reserved for Class D and E net-
works. Class D is used for multicast addresses (224239) and Class E (240
255) for scientific purposes, but I'm not going into these types of addresses
in this book (and you don't need to know them for the exam).

Network Addresses: Special Purpose

Some IP addresses are reserved for special purposes, so network administra-
tors can't ever assign these addresses to nodes. Table 3.3 lists the members
of this exclusive little club and why they're included in it.

T A B L E 3 . 3

Reserved IP Addresses

Address

Function

Network address
of all 0s

Interpreted to mean "this network or segment."

Network address
of all 1s

Interpreted to mean "all networks."

Network 127.0.0.1

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

Node address of
all 0s

Interpreted to mean "this node."

Node address of
all 1s

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 0s

Used by Cisco routers to designate the default
route.

Entire IP address set
to all 1s (same as
255.255.255.255)

Broadcast to all nodes on the current network;
sometimes called an "all 1s broadcast."

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