Special Ip Addresses; Subnetting And Masking - 3Com 4510G Configuration Manual

Table 1-1 IP address classes and ranges
Class
0.0.0.0 to
A
127.255.255.255
128.0.0.0 to
B
191.255.255.255
192.0.0.0 to
C
223.255.255.255
224.0.0.0 to
D
239.255.255.255
240.0.0.0 to
E
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 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.
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 whereas
the part containing consecutive zeros identifies the host ID.
Figure 1-2 shows how a Class B network is subnetted.
Figure 1-2 Subnet a Class B network
Address range
The IP address 0.0.0.0 is used by a host at bootstrap for
temporary communication. 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 sent to the link.
––
––
Multicast addresses.
Reserved for future use except for the broadcast address
255.255.255.255.
Remarks
1-2