Special Ip Addresses; Subnetting And Masking - H3C S5120-SI Series Configuration Manual

Class
D
E

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 broadcasted to all the hosts on the network
192.168.1.0.

Subnetting and masking

Subnetting was developed to address the risk of IP address exhaustion resulting from fast expansion of the
Internet. The idea is to break a network down into smaller networks called subnets by using some bits of
the host ID to create a subnet ID. To identify the boundary between the host ID and the combination of
net ID and subnet ID, masking is used. (When subnetting is not adopted, a mask identifies the boundary
between the net ID and the host ID.)
Each subnet mask comprises 32 bits related to the corresponding bits in an IP address. In a subnet mask:
•
The part containing consecutive ones identifies the combination of net ID and subnet ID.
•
The part containing consecutive zeros identifies the host ID.
Figure 8 shows how a Class B network is subnetted.
Figure 8 Subnetted Class B Network
With or without subnetting, some addresses cannot be assigned to hosts because they are reserved for
special purposes. The address with an all-one host-id is the broadcast address, and the address with the
all-zero host-id is the network address.
As a result, when designing your network, you should note that subnetting somewhat reduces the number
of hosts that can be accommodated. For example, a Class B network can accommodate 65,534 hosts
Address range
224.0.0.0 to
239.255.255.255
240.0.0.0 to
255.255.255.255
Remarks
Multicast addresses.
Reserved for future use except for the broadcast address
255.255.255.255.
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