3Com 2500 manual How a Subnet Mask Is Applied to the IP Address

4-4 CHAPTER 4: ROUTING WITH IP TECHNOLOGY

Take the IP address

IP Address

Network	Subnet and Host
	Apply the subnet mask

Subnet Mask 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0

Result = subnet/host boundary

Networknetwor Subnet Host

Figure 4-3 How a Subnet Mask Is Applied to the IP Address

An example of an IP address that includes network, subnet, and host parts is 158.101.230.52 with a subnet mask of 255.255.255.0. This address is divided as follows:

■158.101 is the network part

■230 is the subnet part

■52 is the host part

Router Interfaces A router interface is the connection between the router and a subnet. In traditional routing models, the interface is the same as the port, since only one interface can exist per port. In the LANplex system’s IP routing model, more than one port can be connected to the same subnet.

Each router interface has an IP address and a subnet mask. This address defines both the number of the network to which the router interface is attached and its host number on that network. A router interface’s IP address serves two functions:

■The IP address is used when sending IP packets to or from the router itself.

■The IP address defines the network and subnet numbers of the segment connected to that interface. See Figure 4-4.