RI2950-24#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
RI2950-24(config)#int fa 0/23
RI2950-24(config-if)#switchport mode trunk
RI2950-24(config-if)#switchport trunk allowed vlan 2,4
RI2950-24(config-if)#exit
RI2950-24(config)#



RI2950-24#sh int trunk
Port        Mode         Encapsulation  Status        Native vlan
Fa0/23      on           802.1q         trunking      1

Port        Vlans allowed on trunk
Fa0/23      2,4

Port        Vlans allowed and active in management domain
Fa0/23      2,4

Port        Vlans in spanning tree forwarding state and not pruned
Fa0/23      2,4

RI2950-24#