i'm just follow step from the sybex study guide - ccna 4th edition book
i'm using Boson NetSim 5.27 simulator...
Router#config
Configuring from terminal, memory, or network [terminal]?
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#interface FastEthernet 0/0
Invalid Command
Router(config)#interface FastEthernet ?
<0-1> Interface
Router(config)#interface FastEthernet 0
Invalid Command
Router(config)#interface FastEthernet0
Invalid Command
