4.2.7 Packet Tracer – Configure Router-on-a-Stick Inter-VLAN Routing (Instructions Answer)

! ==============================================================
!--- 4.2.7 Packet Tracer - Configure Router-on-a-Stick Inter-VLAN Routing
!--- ANSWER SCRIPT FOR SWITCH S1
!--- Usage: from the console or a Telnet/SSH session to S1, enter privileged EXEC mode with "enable", then paste this whole file. Every line beginning with "!" is a comment; IOS ignores it, so pasting a comment by accident is harmless.
!--- S1 starts with no VLANs beyond the default. This script creates VLAN 10 and VLAN 30, assigns the access ports facing PC1 and PC3, and later trunks the uplink to R1 (G0/1) so the router can route between the two VLANs.
! ==============================================================

enable
configure terminal

! --------------------------------------------------------------
!--- Part 1, Step 1: Create VLANs on S1
! --------------------------------------------------------------

!--- Create the two VLANs used in this activity; the lab does not require custom names, so they keep their default VLAN0010 / VLAN0030 names.
vlan 10
vlan 30

! --------------------------------------------------------------
!--- Part 1, Step 2: Assign VLANs to ports
! --------------------------------------------------------------

!--- F0/11 faces PC1 (VLAN 10) and F0/6 faces PC3 (VLAN 30 - see the naming note in the discrepancy summary). Both become access ports in their respective VLAN.
interface FastEthernet0/11
 switchport mode access
 switchport access vlan 10

interface FastEthernet0/6
 switchport mode access
 switchport access vlan 30

! --------------------------------------------------------------
!--- Part 3, Step 2: Enable trunking on the uplink to R1
! --------------------------------------------------------------

!--- G0/1 must carry both VLAN 10 and VLAN 30 to R1's subinterfaces, so it becomes a trunk. Before this command "show vlan" lists G0/1 under VLAN 1; afterwards the interface drops out of that per-VLAN listing entirely (trunk ports aren't shown there).
interface GigabitEthernet0/1
 switchport mode trunk

end

! --------------------------------------------------------------
!--- Operational habit (not explicitly required by this lab): save to NVRAM. (Press Enter when prompted for the destination filename.)
! --------------------------------------------------------------
copy running-config startup-config

! ==============================================================
!--- Verification (Parts 1-3, from S1 and from the PCs):
!---   S1# show vlan brief         -> VLAN 10 shows Fa0/11, VLAN 30 shows Fa0/6
!---   S1# show vlan               -> G0/1 no longer appears under any VLAN once trunked
!---   S1# show interfaces trunk   -> G0/1 trunking, allowed VLANs 10, 30
!---   From PC1, ping 172.17.10.1  -> success (default gateway)
!---   From PC3, ping 172.17.30.1  -> success (default gateway)
!---   From PC1, ping PC3          -> fails until R1's subinterfaces are also configured and up; succeeds once the whole topology is in place
! ==============================================================

! ==============================================================
!--- 4.2.7 Packet Tracer - Configure Router-on-a-Stick Inter-VLAN Routing
!--- ANSWER SCRIPT FOR ROUTER R1
!--- Usage: from the console or a Telnet/SSH session to R1, enter privileged EXEC mode with "enable", then paste this whole file. Every line beginning with "!" is a comment; IOS ignores it, so pasting a comment by accident is harmless.
!--- R1's G0/0 physical interface starts shut down and has no subinterfaces yet. This script builds the two 802.1Q subinterfaces for VLAN 10 and VLAN 30 (the "router-on-a-stick") and brings the physical interface up so both come online.
! ==============================================================

enable
configure terminal

! --------------------------------------------------------------
!--- Part 2, Step 1: Configure subinterfaces on R1 using 802.1Q encapsulation
! --------------------------------------------------------------

!--- Subinterface .10 tags traffic for VLAN 10 and takes the gateway address PC1 expects, straight from the Addressing Table.
interface GigabitEthernet0/0.10
 encapsulation dot1Q 10
 ip address 172.17.10.1 255.255.255.0

!--- Subinterface .30 tags traffic for VLAN 30 and takes the gateway address PC3 expects.
interface GigabitEthernet0/0.30
 encapsulation dot1Q 30
 ip address 172.17.30.1 255.255.255.0

! --------------------------------------------------------------
!--- Part 2, Step 2: Enable the physical interface so the subinterfaces come up
! --------------------------------------------------------------

!--- Subinterfaces are virtual and inherit their up/down state from the parent physical interface - before this command "show ip interface brief" shows both G0/0.10 and G0/0.30 as down. A single "no shutdown" on the physical G0/0 brings both subinterfaces up together; no per-subinterface shutdown toggling is needed.
interface GigabitEthernet0/0
 no shutdown

end

! --------------------------------------------------------------
!--- Operational habit (not explicitly required by this lab): save to NVRAM. (Press Enter when prompted for the destination filename.)
! --------------------------------------------------------------
copy running-config startup-config

! ==============================================================
!--- Verification (Parts 2-3, from R1 and from the PCs):
!---   R1# show ip interface brief -> G0/0, G0/0.10, G0/0.30 all up/up
!---   From PC1, ping 172.17.10.1  -> success (default gateway)
!---   From PC3, ping 172.17.30.1  -> success (default gateway)
!---   From PC1, ping PC3          -> success once S1's G0/1 is also trunked
! ==============================================================