F3726, F3211, F3174, R5135, R3816-HP Firewalls and UTM Devices Network Management Configuration Guide-6PW100

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Class Address ran
g
e Remarks
B
128.0.0.0 to
191.255.255.255
N/A
C
192.0.0.0 to
223.255.255.255
N/A
D
224.0.0.0 to
239.255.255.255
Multicast addresses.
E
240.0.0.0 to
255.255.255.255
Reserved for future use except for the broadcast address
255.255.255.255.
381BSpecial IP addresses
The following IP addresses are for special use and cannot be used as host IP addresses.
• IP address with an all-zero net ID—Identifies a host on the local network. For example, IP address
0.0.0.16 indicates the host with a host ID of 16 on the local network.
• IP address with an all-zero host ID—Identifies a network.
• IP address with an all-one host ID—Identifies a directed broadcast address. For example, a packet
with the destination address of 192.168.1.255 is broadcast to all the hosts on the network
192.168.1.0.
382BSubnetting and masking
Subnetting divides a network into smaller networks called subnets by using some bits of the host ID to
create a subnet ID.
Masking identifies the boundary between the host ID and the combination of net ID and subnet ID.
(When subnetting is not adopted, a mask identifies the boundary between the net ID and the host ID.)
Each subnet mask is made up of 32 bits, which correspond to the bits in an IP address. In a subnet mask,
consecutive ones represent the net ID and subnet ID, and consecutive zeros represent the host ID.
Before being subnetted, Class A, B, and C networks use default masks (also called natural masks)
255.0.0.0, 255.255.0.0, and 255.255.255.0, respectively.
2159HFigure 11 shows how a Class B network is subnetted.
Figure 11 Subnetting a Class B network
Subnetting increases the number of addresses that cannot be assigned to hosts. After being subnetted,
a network can accommodate fewer hosts.
For example, a Class B network without subnetting can accommodate 1022 more hosts than the same
network subnetted into 512 subnets.