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.