Subnet Portion
IP Addressing
E-2
Consider the IP address 36.1.3.4. This address is a Class A address; therefore, the network
portion of the address is 36.0.0.0, and the host portion is 1.3.4.
Subnet Portion
The subnet portion of the IP address represents which subnetwork the address is from.
Subnetworks are formed when an IP network is broken down into smaller networks using
a subnet mask.
A router is required between all networks and all subnetworks. Generally, nodes can send
packets directly only to nodes on their own subnetwork. All packets destined for other
subnets are sent to a router on the local network.
Host Portion
The host portion of the IP address is a unique number assigned to identify the node.
Network Address
A host address with all host bits set to 0 addresses the network as a whole (for example, in
routing entries).
Figure E-1: Sample Network Address
Broadcast Address
A host address with all host bits set to 1 is the broadcast address, meaning for “for every
station.”
Figure E-2: Sample Broadcast Address
Note:
Network and broadcast addresses must not be used as a host address;
for example, 192.168.0.0 identifies the entire network, and
192.168.0.255 identifies the broadcast address.
192.168.0.0
192.168.0.255
