Tab
IP address clas
le 8-1
ses and ranges
Address range
De
Class
scription
A
0.0.0.0 to 127.255.255.255
st at bootstrap when it
does not know its IP address. This address is never
a valid destination address.
Addresses starting with 127 are reserved for
loopback test. Packets destined to these addresses
are processed locally as input packets rather than
Address 0.0.0.0 means this host no this network.
This address is used by a ho
sent to the link.
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 Multicast
address.
E
240.0.0.0 to 255.255.255.255
Reserved for future use except for the broadcast
address 255.255.255.255.
s
twork.
Subnetting and Masking
stion resulting from fast expansion of
works called subnets by using some
ary between the host ID and the
g bits in an IP address. In a subnet
on of net ID and subnet ID whereas
e part containing consecutive zeros identifies the host ID.
Special Case IP Addresse
The following IP addresses are for special use, and they cannot be used as host IP addresses:
IP address with an all-zeros 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-zeros host ID: Identifies a ne
IP address with an all-ones 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 was developed to address the risk of IP address exhau
the Internet. The idea is to break a network down into smaller net
bits of the host ID to create a subnet ID. To identify the bound
combination of net ID and subnet ID, masking is used.
Each subnet mask comprises 32 bits related to the correspondin
mask, the part containing consecutive ones identifies the combinati
th
Figure 8-2
shows how a Class B network is subnetted.
Figure 8-2
Subnet a Class B network
While allowing you to create multiple logical networks within a single Class A, B, or C network,
subnetting is transparent to the rest of the Internet. All these networks still appear as one. As subnetting
8-2
