Each VLAN must correspond to a unique IP subnet. If two devices in the same VLAN have different subnet addresses, they cannot communicate. This is a common problem, and it is easy to solve by identifying the incorrect configuration and changing the subnet address to the correct one.
In Figure 1, PC1 cannot connect to the Web/TFTP server shown.
A check of the IP configuration settings of PC1 shown in Figure 2 reveals the most common error in configuring VLANs: an incorrectly configured IP address. PC1 is configured with an IP address of 172.172.10.21, but it should have been configured with 172.17.10.21.
The PC1 Fast Ethernet configuration dialog box shows the updated IP address of 172.17.10.21. In Figure 3, the output on the bottom reveals that PC1 has regained connectivity to the Web/TFTP server found at IP address 172.17.10.30.