VLAN Implementation and Troubleshooting in a Switched Network

Introduction

As the network administrator of a medium-sized company, VLANs were implemented to optimize network performance and security. The VLAN configuration is managed using VLAN Trunking Protocol (VTP) across multiple Cisco switches. However, after implementation, the Finance department (VLAN 20) reported connectivity issues. This report details the troubleshooting process and resolutions.

Diagram Overview:

VLAN Configuration Overview

VLAN Scenario :

VLAN 10: Marketing
VLAN 20: Finance
VLAN 30: IT

Network Setup:

Multiple Cisco switches are connected via trunk links.
VTP enabled to manage VLAN configurations.
802.1Q encapsulation is used for trunking in networking.
Access Ports are assigned to respective VLANs based on department needs.

Switch configuration

First, change switches 2,3 and 4 to transparent mode, while switches 5,6 and 7 to client mode.
Create a VLAN in Switch 1.
Set a domain name and password.
Access PC ports in their respective VLANs in Switches 5, 6, and 7.
Assign IP addresses to the PCs.
Trunk all switch ports.

Switch 1

The switch is set to server mode by default.

Create VLAN 10,20,30

  switch(config)#vlan 10
  switch(config)#vlan 20
  switch(config)#vlan 30

VTP domain name and VTP password

  switch(config)# vtp domain shreiya
  switch(config)# vtp password 123

Trunk

  switch(config)# in range fast 0/1-3
  Switch(config-if-range)# switch mode access
  Switch(config-if-range)# switch mode trunk

Switch 2

Change VTP mode to transparent
```
  switch(config)# vtp mode transparent
```

Trunk

  switch(config)# in range fast 0/1-2
  Switch(config-if-range)# switch mode access
  Switch(config-if-range)# switch mode trunk

Create VLAN 10,20,30

  switch(config)#vlan 10
  switch(config)#vlan 20
  switch(config)#vlan 30

Switch 3

Change VTP mode to transparent
```
  switch(config)# vtp mode transparent
```

Trunk

  switch(config)# in range fast 0/1-2
  Switch(config-if-range)# switch mode access
  Switch(config-if-range)# switch mode trunk

Create VLAN 10,20,30

  switch(config)#vlan 10
  switch(config)#vlan 20
  switch(config)#vlan 30

Switch 4

Change VTP mode to transparent
```
  switch(config)# vtp mode transparent
```

Trunk

  switch(config)# in range fast 0/1-2
  Switch(config-if-range)# switch mode access
  Switch(config-if-range)# switch mode trunk

create VLANs 10, 20, and 30.

  switch(config)#vlan 10
  switch(config)#vlan 20
  switch(config)#vlan 30

Switch 5

Change VTP mode to Client
```
  switch(config)# vtp mode client
```

Access port in VLAN.

  switch(config)# in fast 0/2
  switch(config-if)# switchport access vlan 10
  switch(config)# in fast 0/3
  switch(config-if)# switchport access vlan 20
  switch(config)# in fast 0/4
  switch(config-if)# switchport access vlan 30

Trunk

  switch(config) in fast 0/1
  switch(config-if)# switchport mode access
  switch(config-if)# switchport mode trunk

Switch 6

Change VTP mode to Client
```
  switch(config)# vtp mode client
```

Access port in VLAN

  switch(config)# in fast 0/2
  switch(config-if)# switchport access vlan 10
  switch(config)# in fast 0/3
  switch(config-if)# switchport access vlan 20
  switch(config)# in fast 0/4
  switch(config-if)# switchport access vlan 30

Trunk

  switch(config) in fast 0/1
  switch(config-if)# switchport mode access
  switch(config-if)# switchport mode trunk

Switch 7

Change VTP mode to Client
```
  switch(config)# vtp mode client
```

Access port in VLAN.

  switch(config)# in fast 0/2
  switch(config-if)# switchport access vlan 10
  switch(config)# in fast 0/3
  switch(config-if)# switchport access vlan 20
  switch(config)# in fast 0/4
  switch(config-if)# switchport access vlan 30

Trunk

  switch(config)# in fast 0/1
  switch(config-if)# switchport mode access
  switch(config-if)# switchport mode trunk

IP Addressing

Switch 5

VLAN 10 :- 192.168.10.1 /24

VLAN 20 :- 192.168.20.1 /24

VLAN 30 :- 192.168.30.1 /24

Switch 6

VLAN 10 :- 192.168.10.2 /24

VLAN 20 :- 192.168.20.2 /24

VLAN 30 :- 192.168.30.2 /24

Switch 7

VLAN 10 :- 192.168.10.3 /24

VLAN 20 :- 192.168.20.3 /24

VLAN 30 :- 192.168.30.3 /24

Objective

Please check all switches to see if VLANs are present.
Please verify all switches to ensure they are configured as trunk switches.
Access PC ports within their respective VLAN.

Please check whether all departments are connected.

Identified Issues

Devices in VLAN 20 (Finance) could not communicate with some PCs.
Some switches were not reflecting the VLAN updates.

Troubleshooting

Verify VLAN Configuration on All Switches
```
 switch(config)# do show vlan
```
Check VTP configuration.
```
 switch(config)# show vtp status
```
Inspect trunk links.
```
 switch(config)# do show run
```
See the port access.
```
 switch(config)# do show run
```
Check IP address on PC:

Resolution and Fixes

1. Correct VLAN Assignments:

Added VLAN 20 on missing switches:
Reassigned Finance department ports:

2. Fix VTP Configuration

VTP domain name across switches
Change VTP mode (if needed):

3. Ensure VLAN 20 is Allowed on Trunks

Allowed VLAN 20 on all switches:

Final Testing & Results

After applying the fixes, the following tests were conducted:

VLAN 20 Verification:
- do show vlan confirmed VLAN 20 existed on all switches.
VTP Synchronization:
- do show vtp status verified all switches had the correct revision number.
Trunk Links Check:
- do show run showed VLAN 20 was allowed.
Ping and Tests:
- Successful communication between Finance department devices.

Outcome: The Finance department regained full network connectivity.

Conclusion:

The root causes of the issue were:

VLAN 20 missing on some switches due to VTP synchronization issues.
VLAN 20 not allowed on some trunk links.
Incorrect VLAN assignments on Finance department access ports.
Incorrect IP address.