H3C Technologies H3C SecBlade NetStream Cards - Manual (Page 81)

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Class Address range Remarks
C
192.0.0.0 to
223.255.255.255
––
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.
Special IP addresses
The following IP addresses are for special use, and they 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 will be broadcast to all the hosts on the network
192.168.1.0.
Subnetting and masking
Subnetting divides a network down 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.
Each subnet mask comprises 32 bits that 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 these default masks (also called natural masks):
255.0.0.0, 255.255.0.0, and 255.255.255.0 respectively.
Figure 23 shows how a Class B network is subnetted.
Figure 23 Subnet a Class B network
Subnetting increases the number of addresses that cannot be assigned to hosts. Therefore, using subnets
means accommodating somewhat fewer hosts
For example, a Class B network without subnetting can accommodate 1022 more hosts than the same
network subnetted into 512 subnets.
• Without subnetting: 65,534 hosts (2 16 – 2). (The two deducted addresses are the broadcast
address, which has an all-one host ID, and the network address, which has an all-zero host ID.)