3.4.5-packet-tracer---configure-trunks

/* S1, S2 and S3 */
enable
show vlan

/* S1 */
enable
conf t
interface range g0/1-2
switchport mode trunk
switchport trunk native vlan 99
end

/* S2 */
show interface trunk
conf t
interface g0/1
switchport trunk native vlan 99
end

/* S3 */
show interface trunk
conf t
interface g0/2
switchport trunk native vlan 99
end