Appendix B IP Addresses and Subnetting
IP Address Conflicts
Each device on a network must have a unique IP address. Devices with duplicate IP addresses on the same network will not be able to access the Internet or other resources. The devices may also be unreachable through the network.
Conflicting Computer IP Addresses Example
More than one device can not use the same IP address. In the following example computer A has a static (or fixed) IP address that is the same as the IP address that a DHCP server assigns to computer B which is a DHCP client. Neither can access the Internet. This problem can be solved by assigning a different static IP address to computer A or setting computer A to obtain an IP address automatically.
Figure 54 Conflicting Computer IP Addresses Example
Conflicting Router IP Addresses Example
Since a router connects different networks, it must have interfaces using different network numbers. For example, if a router is set between a LAN and the Internet (WAN), the router’s LAN and WAN addresses must be on different subnets. In the following example, the LAN and WAN are on the same subnet. The LAN computers cannot access the Internet because the router cannot route between networks.
Figure 55 Conflicting Computer IP Addresses Example
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