4.4.9 Packet Tracer - Troubleshoot Inter-VLAN Routing – Physical Mode Answers
Topology
Addressing Table
| Device | Interface | IP Address | Subnet Mask | Default Gateway |
|---|---|---|---|---|
| R1 | G0/0/1.3 | 10.3.0.1 | 255.255.255.0 | N/A |
| G0/0/1.4 | 10.4.0.1 | 255.255.255.0 | ||
| G0/0/1.13 | 10.13.0.1 | 255.255.255.0 | ||
| S1 | VLAN 3 | 10.3.0.11 | 255.255.255.0 | 10.3.0.1 |
| S2 | VLAN 3 | 10.3.0.12 | 255.255.255.0 | 10.3.0.1 |
| PC-A | NIC | 10.4.0.50 | 255.255.255.0 | 10.4.0.1 |
| PC-B | NIC | 10.13.0.50 | 255.255.255.0 | 10.13.0.1 |
VLAN Table
| VLAN | Name | Interface Assigned |
|---|---|---|
| 3 | Management | S1: VLAN 3 S2: VLAN 3 |
| 4 | Operations | S1: F0/6 |
| 7 | ParkingLot | S1: F0/2-4, F0/7-24, G0/1-2 S2: F0/2-17, F0/19-24, G0/1-2 |
| 8 | Native | N/A |
| 13 | Maintenance | S2: F0/18 |
Objectives
- Part 1: Evaluate Network Operation
- Part 2: Gather Information, Create an Action Plan, and Implement Corrections
Background / Scenario
All the network devices in this Packet Tracer Physical Mode (PTPM) activity have been preconfigured to include intentional errors that are keeping the inter-VLAN routing from working. Your task is to evaluate the network, identify, and correct the configuration errors to restore full inter-VLAN connectivity. You may find errors with the configurations which are not directly related to inter-VLAN routing. These errors impact the ability of the network devices to perform this function.
Note: The design approach used in this activity is to assess your ability to configure and troubleshoot interVLAN routing only. This design may not reflect networking best practices.
Instructions
Part 1: Evaluate Network Operation
Requirements:
- No VLAN 7 traffic is allowed on the trunks because there are no devices in VLAN 7.
- VLAN 8 is the native VLAN.
- All trunks are static.
- End to end connectivity.
a. Use the laptop computer and appropriate cable to console into the network devices for testing and configuration purposes. The login password on all network devices is “cisco” and the enable password is “class”. You can click and drag the console connection from the console port of one device to another, but you will have to start a new terminal session.
b. Use the ping command to test the following criteria and record the results in the table below.
| From | To | Ping Results |
|---|---|---|
| R1 | S1 VLAN 3 (10.3.0.11) | Unsuccessful |
| S2 VLAN 3 (10.3.0.12) | Unsuccessful | |
| PC-A (10.4.0.50) | Unsuccessful | |
| PC-B (10.13.0.50) | Unsuccessful | |
| S1 | S2 VLAN 3 (10.3.0.12) | Unsuccessful |
| PC-A (10.4.0.50) | Unsuccessful | |
| PC-B (10.13.0.50) | Unsuccessful | |
| S2 | PC-A (10.4.0.50) | Unsuccessful |
| PC-B (10.13.0.50) | Unsuccessful |
Part 2: Gather Information, Create an Action Plan, and Implement Corrections
a. For each requirement that is not met, gather information by examining the running configuration and the routing tables to develop a hypothesis for what is causing the malfunction.
b. Create an action plan that you think will fix the issue. Develop a list of all the commands you intend to issue to fix the issue, and a list of all the commands you need to revert the configuration, should your action plan fail to correct the issue.
Hint: If you need to reset a switchport to default configuration, use the default interface interface name command.
As an example for F0/10:
S1(config)# default interface f0/10
c. Execute your action plans one at a time for each criterion that fails and record the fix actions.
Device Running Configuration (Before Fix)
Discrepancy Table
| # | Device | Error | Evidence | Fix |
|---|---|---|---|---|
| 1 | R1 | Native VLAN flag placed on the wrong subinterface — G0/0/1.4 has encapsulation dot1Q 4 native instead of G0/0/1.8 |
Running-config shows encapsulation dot1Q 4 native under G0/0/1.4; both S1 and S2 configure switchport trunk native vlan 8, confirming VLAN 8 is the intended native VLAN, not VLAN 4 |
Apply encapsulation dot1Q 8 native under interface GigabitEthernet0/0/1.8 — IOS allows only one native subinterface per physical port, so this automatically clears the flag from .4 |
| 2 | S1 | F0/5 (uplink to R1) is configured as an access port in VLAN 3 instead of a trunk |
Running-config shows switchport access vlan 3 / switchport mode access under FastEthernet0/5, but the topology requires this link to carry VLAN 3, 4, 8, and 13 to R1's subinterfaces |
default interface FastEthernet0/5 (per the lab's own hint) to clear the leftover access config, then rebuild it as switchport mode trunk, switchport trunk native vlan 8, switchport trunk allowed vlan 3,4,8,13 |
| 3 | S1 | F0/1 (uplink to S2) has no native VLAN set (defaults to VLAN 1) and its allowed-VLAN list is incomplete |
Running-config shows switchport trunk allowed vlan 4,8,13 with no switchport trunk native vlan line; the embedded syslog %CDP-4-NATIVE_VLAN_MISMATCH: ...FastEthernet0/1 (1), with S2 FastEthernet0/1 (8) directly confirms the mismatch |
Add switchport trunk native vlan 8; tighten the allowed list to 3,13 — VLAN 3 is needed for S1/S2/R1 management reachability, VLAN 13 for PC-B's traffic; VLAN 4 has no device on S2's side and VLAN 8 carries no host traffic (CDP native-VLAN matching isn't affected by allowed-VLAN pruning) |
| 4 | S2 | F0/1 (uplink to S1) allows VLAN 4 unnecessarily and is missing both VLAN 3 and VLAN 13 |
Running-config shows switchport trunk allowed vlan 4,8; native VLAN 8 is already correctly set here (S1 was the side missing it) |
Change the allowed list to 3,13, mirroring the corrected S1 side |
| 5 | S1 | VLAN 13 may never have been created in S1's local VLAN database | show running-config never displays VLAN database entries (they live in vlan.dat); S1 has no local access port in VLAN 13 (only S2's F0/18 does), so it can't be ruled out from this capture alone |
Add vlan 13 / name Maintenance — harmless to re-declare even if it already existed |
Device Configs - Final (Fix script)
ROUTER R1
! ============================================================== !--- 4.4.9 Packet Tracer - Troubleshoot Inter-VLAN Routing - Physical Mode !--- FIX SCRIPT FOR ROUTER R1 !--- Usage: from the console, enter privileged EXEC mode with "enable" (password "class" per the lab), then paste this whole file. Every line beginning with "!" is a comment; IOS ignores it, so pasting a comment by accident is harmless. !--- Confirmed error: the "native" keyword sits on the wrong subinterface (G0/0/1.4 instead of G0/0/1.8). Only one subinterface per physical interface can be native, so simply applying "native" to .8 automatically clears it from .4 - no need to touch .4 at all. ! ============================================================== enable configure terminal ! -------------------------------------------------------------- !--- Fix (#1 in the discrepancy table): move the native VLAN flag to subinterface .8, where it belongs ! -------------------------------------------------------------- !--- IOS allows only one native subinterface per physical port - setting it here automatically removes the "native" designation from G0/0/1.4, which is exactly the fix needed. interface GigabitEthernet0/0/1.8 encapsulation dot1Q 8 native 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 (Part 1's Ping Test Results table, once S1's fixes are also applied): !--- R1# show interfaces g0/0/1.4 -> no longer shows "native" in the encapsulation line !--- R1# show interfaces g0/0/1.8 -> now shows "802.1Q Virtual LAN, Native VLAN 8" !--- R1# ping 10.4.0.50 (PC-A) -> success (this was the ping actually broken by the native-flag bug) !--- R1# ping 10.13.0.50 (PC-B) -> success (needs S1's F0/5 trunk fix too) ! ==============================================================
SWITCH S1
! ============================================================== !--- 4.4.9 Packet Tracer - Troubleshoot Inter-VLAN Routing - Physical Mode !--- FIX SCRIPT FOR SWITCH S1 !--- Usage: from the console, enter privileged EXEC mode with "enable" (password "class" per the lab), then paste this whole file. Every line beginning with "!" is a comment; IOS ignores it, so pasting a comment by accident is harmless. !--- Confirmed errors: (1) F0/5 (to R1) is an access port in VLAN 3 instead of a trunk. (2) F0/1 (to S2) has no native VLAN set and is missing VLAN 3 from its allowed list. (3) VLAN 13 may never have been created in S1's local VLAN database - "show running-config" never displays VLAN database entries (they live in vlan.dat), so this can't be ruled out from the capture alone; the line below is harmless to run either way. ! ============================================================== enable configure terminal ! -------------------------------------------------------------- !--- Fix (#2 in the discrepancy table): reset F0/5 (the link to R1) to a clean slate, then trunk it ! -------------------------------------------------------------- !--- "default interface" wipes the leftover "switchport access vlan 3" / access mode completely (this is the lab's own documented hint for resetting a port), so the trunk below starts from a clean state. default interface FastEthernet0/5 interface FastEthernet0/5 switchport mode trunk switchport trunk native vlan 8 switchport trunk allowed vlan 3,4,8,13 ! -------------------------------------------------------------- !--- Fix (#3 in the discrepancy table): correct F0/1 (the link to S2) - native VLAN and a tighter allowed list ! -------------------------------------------------------------- !--- Native vlan 8 clears the CDP mismatch against S2. The allowed list is scoped to what actually needs to cross THIS link: VLAN 3 (management, both switches + R1 share the subnet) and VLAN 13 (PC-B's traffic transits S2 -> S1 -> R1). VLAN 4 has no device on S2's side, so it doesn't need to cross here; VLAN 8 has no host traffic, and the native-vlan match between S1 and S2 doesn't depend on it being in the allowed list (CDP runs regardless of VLAN pruning). interface FastEthernet0/1 switchport trunk native vlan 8 switchport trunk allowed vlan 3,13 ! -------------------------------------------------------------- !--- Defensive fix (#5 in the discrepancy table): make sure VLAN 13 actually exists in S1's local VLAN database ! -------------------------------------------------------------- !--- S1 has no access port in VLAN 13 (only S2's F0/18 does), so it's possible VLAN 13 was never created here at all. Re-declaring it is harmless if it already existed. vlan 13 name Maintenance 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 (Part 1's Ping Test Results table): !--- S1# show interfaces trunk -> F0/1 and F0/5 both trunking, native VLAN 8 on both !--- S1# show interface f0/1 switchport -> "Native VLAN mismatch" message stops appearing !--- S1# show vlan brief -> VLAN 13 now present !--- S1# ping 10.3.0.1 (R1) -> success !--- S1# ping 10.3.0.12 (S2) -> success (needs S2's F0/1 fix too) !--- S1# ping 10.4.0.50 (PC-A) -> success !--- S1# ping 10.13.0.50 (PC-B) -> success ! ==============================================================
SWITCH S2
! ============================================================== !--- 4.4.9 Packet Tracer - Troubleshoot Inter-VLAN Routing - Physical Mode !--- FIX SCRIPT FOR SWITCH S2 !--- Usage: from the console, enter privileged EXEC mode with "enable" (password "class" per the lab), then paste this whole file. Every line beginning with "!" is a comment; IOS ignores it, so pasting a comment by accident is harmless. !--- Confirmed error: F0/1 (the trunk to S1) allows VLAN 4, which no device on S2 needs, while VLAN 3 was missing entirely. Native VLAN 8 is already correctly set here - S1 was the side missing it. ! ============================================================== enable configure terminal ! -------------------------------------------------------------- !--- Fix (#4 in the discrepancy table): tighten F0/1's allowed-VLAN list to match what actually needs to cross this link ! -------------------------------------------------------------- !--- Mirrors S1's F0/1: VLAN 3 (management) and VLAN 13 (PC-B's traffic to R1 via S1) are the only VLANs with real traffic on this link. VLAN 4 has no device on S2 and is dropped; VLAN 8 (native) carries no host traffic and doesn't need to be in the allowed list for the native-VLAN match with S1 to hold (CDP isn't affected by VLAN pruning). interface FastEthernet0/1 switchport trunk allowed vlan 3,13 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 (Part 1's Ping Test Results table): !--- S2# show interfaces trunk -> F0/1 trunking, native VLAN 8, VLANs 3,13 allowed !--- S2# ping 10.3.0.1 (R1) -> success (needs S1's F0/5 fix too) !--- S2# ping 10.3.0.11 (S1) -> success !--- S2# ping 10.4.0.50 (PC-A) -> success (needs S1's F0/5 fix too) !--- S2# ping 10.13.0.50 (PC-B) -> success (local, S2's own F0/18) ! ==============================================================
