3Com 7757 Configuration Manual page 128

128 C 15: IP A
HAPTER DDRESS
Subnet and Mask
C
ONFIGURATION
Table 73 Classes and ranges of IP addresses
Network
type Address range
A 0.0.0.0 to
127.255.255.255
B 128.0.0.0 to
191.255.255.255
C 192.0.0.0 to
223.255.255.255
D 224.0.0.0 to
239.255.255.255
E 240.0.0.0 to
255.255.255.254
Others 255.255.255.255
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
IP address, the part corresponding to the "1" bits in the mask is the subnet
IP network
range Description
1.0.0.0 to An IP address with all 0s host ID is a
■
126.0.0.0 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.
128.0.0.0 to An IP address with all 0s host ID is a
■
191.255.0.0 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.
192.0.0.0 to An IP address with all 0s host ID is a
■
223.255.255.0 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.
None Class D addresses are multicast
addresses.
None These IP addresses are reserved for
future use.
255.255.255.25 255.255.255.255 is used as a LAN
5 broadcast address.