4.4.8 Packet Tracer – Troubleshoot Inter-VLAN Routing (Instructions Answer)

R1# show ip interface brief
R1# show interface g0/1.10
R1# show interface g0/1.30
S1# show interface trunk

! ==============================================================
!--- 4.4.8 Packet Tracer - Troubleshoot Inter-VLAN Routing
!--- ANSWER SCRIPT FOR ROUTER R1 (troubleshooting fix - not a full rebuild)
!--- 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. This script assumes R1 is already otherwise configured (per the .pka starting state) and only applies the fixes documented in Part 1's Documentation Table.
!--- Problem (Documentation Table, row 4): the subinterface VLAN tags are swapped versus the Addressing Table. Problem (row 1): G0/1.10 is administratively shut down even though the physical G0/1 is up. Both are fixed below.
! ==============================================================

enable
configure terminal

! --------------------------------------------------------------
!--- Documentation Table, row 4: fix the swapped subinterface VLAN assignments
! --------------------------------------------------------------

!--- Clear the incorrect dot1q tag on each subinterface first, then reapply the correct VLAN and re-enter the IP address per the Addressing Table - removing the encapsulation can drop the previously configured IP as a side effect, so it must be re-entered either way (this is exactly what the documented solution means by "reenter the correct IP address information").
interface GigabitEthernet0/1.10
 no encapsulation dot1q
 encapsulation dot1q 10
 ip address 172.17.10.1 255.255.255.0

interface GigabitEthernet0/1.30
 no encapsulation dot1q
 encapsulation dot1q 30
 ip address 172.17.30.1 255.255.255.0

! --------------------------------------------------------------
!--- Documentation Table, row 1: bring up the administratively-down subinterface
! --------------------------------------------------------------

!--- The physical G0/1 was already up; only the .10 subinterface itself had been shut down independently (subinterfaces can carry their own admin state separate from the parent). G0/1.30 was never reported as down, so it's left alone.
interface GigabitEthernet0/1.10
 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 1 & 3, from R1 and the PCs):
!---   R1# show ip interface brief -> G0/1, G0/1.10, G0/1.30 all up/up
!---   R1# show interface g0/1.10  -> 802.1Q vtag 10, matches PC1's VLAN
!---   R1# show interface g0/1.30  -> 802.1Q vtag 30, matches PC3's VLAN
!---   From PC1, ping 172.17.10.1  -> success (default gateway)
!---   From PC3, ping 172.17.30.1  -> success once PC3's own gateway is corrected too (see the PC note in chat)
!---   From PC1, ping PC3          -> success once S1's trunk fix and PC3's gateway fix are also in place
! ==============================================================

! ==============================================================
!--- 4.4.8 Packet Tracer - Troubleshoot Inter-VLAN Routing
!--- ANSWER SCRIPT FOR SWITCH S1 (troubleshooting fix - not a full rebuild)
!--- 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. This script assumes S1 is already otherwise configured (VLANs, access ports for PC1/PC3) and only applies the fix documented in Part 1's Documentation Table.
!--- Problem (Documentation Table, row 3): G0/1, the uplink to R1, is configured as an access port instead of a trunk, so it can't carry both VLAN 10 and VLAN 30 to R1's subinterfaces.
! ==============================================================

enable
configure terminal

! --------------------------------------------------------------
!--- Documentation Table, row 3: change G0/1 from access to trunk mode
! --------------------------------------------------------------

!--- Without this, R1's two subinterfaces never see any VLAN-tagged traffic at all, no matter how correctly they're configured on the router side.
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 the PCs):
!---   S1# show interfaces trunk -> G0/1 trunking, VLANs 10 and 30 allowed
!---   S1# show vlan brief       -> G0/1 no longer listed under VLAN 1 (trunk ports aren't shown there)
!---   From PC1, ping PC3        -> success once R1's fixes and PC3's gateway fix are also in place
! ==============================================================