Special Ip Addresses; Subnetting And Masking - HP 6125G Configuration Manual

Class
D
E

Special 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 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.
(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 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 the following default masks (also called natural
masks): 255.0.0.0, 255.255.0.0, and 255.255.255.0 respectively.
Figure 12 shows how a Class B network is subnetted.
Figure 12 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.
Without subnetting—65,534 hosts (2
•
address, which has an all-one host ID, and the network address, which has an all-zero host ID.)
• With subnetting—Using the first 9 bits of the host-id for subnetting provides 512 (2
However, only 7 bits remain available for the host ID. This allows 126 (2
a total of 64,512 hosts (512 × 126).
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.
16 – 2). (The two deducted addresses are the broadcast
20
9 ) subnets.
7 – 2) hosts in each subnet,