3Com Switch 7750 Configuration Guide Guide

122 CHAPTER 14: IP ADDRESS CONFIGURATION
Subnet and Mask The traditional IP address classification method wastes IP addresses greatly. In
order to make full use of the available IP addresses, the concepts of mask and
subnet were introduced.
A mask is a 32-bit number corresponding to an IP address. The number consists of
1s and 0s. A mask is defined as follows: the bits of the network number and
subnet number are set to 1, and the bits of the host number are set to 0. The
mask divides the IP address into two parts: subnet address and host address. In an
Tabl e 65 Classes and ranges of IP addresses
Network type Address range
IP network
range
Description
A
0.0.0.0 to
127.255.255.255
1.0.0.0 to
126.0.0.0
■ An IP address with all 0s host ID
is a network address and is used
for network routing.
■ An IP address with all 1s host ID
is a broadcast address and is
used for broadcast to all hosts
on the network.
■ The IP address 0.0.0.0 is used by
hosts when they are booted but
is not used afterward.
■ An IP address with all 0s
network ID represents a specific
host on the local network and
can be used as a source address
but cannot be used as a
destination address.
■ All the IP addresses in the
format of 127.X.Y.Z are
reserved for loopback test and
the packets sent to these
addresses will not be output to
lines; instead, they are
processed internally and
regarded as incoming packets.
B
128.0.0.0 to
191.255.255.255
128.0.0.0 to
191.255.0.0
■ An IP address with all 0s host ID
is a network address and is used
for network routing.
■ An IP address with all 1s host ID
is a broadcast address and is
used for broadcast to all hosts
on the network.
C
192.0.0.0 to
223.255.255.255
192.0.0.0 to
223.255.255.0
■ An IP address with all 0s host ID
is a network address and is used
for network routing.
■ An IP address with all 1s host ID
is a broadcast address and is
used for broadcast to all hosts
on the network.
D
224.0.0.0 to
239.255.255.255
None
Class D addresses are multicast
addresses.
E
240.0.0.0 to
255.255.255.254
None
These IP addresses are reserved for
future use.
Others 255.255.255.255 255.255.255.255
255.255.255.255 is used as a LAN
broadcast address.