This document configures subinterfaces on router R1's FastEthernet 0/0 port for VLANs 15, 25, and 55. Interface fa0/0.15 is configured with dot1q encapsulation for VLAN 15 and IP address 10.10.15.1/24. Interface fa0/0.25 is configured similarly for VLAN 25. Interface fa0/0.55 is configured as a native VLAN with dot1q encapsulation and IP address 10.10.55.1/24. The no shutdown command activates interface fa0/0.