VLANCCNA 200-301

VTP Domain Name Mismatch — VLANs Not Synchronizing

Presenting Symptom

VLANs configured on the VTP server are not appearing on VTP client switches; show vlan brief shows only default VLANs on clients.

Network Context

A small branch office with three Cisco Catalyst 2960 switches running IOS 15.0. One switch is configured as VTP server, the other two as VTP clients. All switches are interconnected via trunk links. The VTP domain name is manually set on each switch, but a typo on the client switches prevents synchronization.

Diagnostic Steps

Check VTP status on client switch

show vtp status

VTP Version                      : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 255
Number of existing VLANs        : 5
VTP Operating Mode              : Client
VTP Domain Name                 : Branch_Office
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x00 0x00 0x00 ...
Configuration last modified by 0.0.0.0 at 0-0-00 00:00:00
Local updater ID is 0.0.0.0 (no valid interface)

Look at VTP Domain Name and Configuration Revision. If domain name is misspelled (e.g., 'Branch_Offce'), it won't match the server. Also, revision number 0 indicates no VLAN updates received.

Check VTP status on server switch

show vtp status

VTP Version                      : 2
Configuration Revision          : 10
Maximum VLANs supported locally : 255
Number of existing VLANs        : 15
VTP Operating Mode              : Server
VTP Domain Name                 : Branch_Office
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x12 0x34 ...
Configuration last modified by 192.168.1.1 at 01-01-25 12:00:00

Server shows correct domain name 'Branch_Office' and revision 10. Compare domain names between server and client; mismatch prevents synchronization.

Verify trunk links between switches

show interfaces trunk

Port        Mode             Encapsulation  Status        Native vlan
Gi0/1       on               802.1q         trunking      1

Port        Vlans allowed on trunk
Gi0/1       1-4094

Port        Vlans allowed and active in management domain
Gi0/1       1,10,20,30

Port        Vlans in spanning tree forwarding state and not pruned
Gi0/1       1,10,20,30

Ensure trunk is up and VLANs are allowed. If trunk is down or not allowing VLANs, VTP updates won't pass. But here trunk is fine.

Check VTP domain name configuration on client

show running-config | include vtp

vtp mode client
vtp domain Branch_Offce

Notice the typo: 'Branch_Offce' vs correct 'Branch_Office'. This mismatch prevents VTP advertisements from being accepted.

Root Cause

The VTP domain name on the client switches is misspelled as 'Branch_Offce' instead of 'Branch_Office' as configured on the VTP server. VTP requires an exact domain name match for switches to exchange VLAN information; a mismatch causes clients to ignore VTP advertisements and maintain only default VLANs.

Resolution

On each client switch, correct the VTP domain name: configure terminal vtp domain Branch_Office end This command sets the VTP domain name to match the server. After correction, the client will synchronize VLANs from the server. Ensure the VTP password also matches if configured (not used here).

Verification

On the client switch, run: show vtp status Expected output: VTP Operating Mode : Client VTP Domain Name : Branch_Office Configuration Revision : 10 Number of existing VLANs : 15 Also run: show vlan brief Expected output includes the VLANs from the server (e.g., VLAN 10, 20, 30).

Prevention

1. Use a consistent VTP domain name across all switches, preferably via a configuration template or automation. 2. Enable VTP pruning and VTP version 2 for better scalability and consistency. 3. Consider using VTP transparent mode or manual VLAN configuration to avoid dependency on VTP synchronization.

CCNA Exam Relevance

On the CCNA 200-301 exam, VTP domain name mismatch is a common troubleshooting scenario. Questions may present a drag-and-drop where you must identify the cause (domain name mismatch) and the fix (correct domain name). The exam tests understanding that VTP requires identical domain names and that a mismatch prevents VLAN synchronization. Key fact: VTP advertisements are only accepted if the domain name and password (if configured) match.

Exam Tips

Memorize that 'show vtp status' displays the domain name and revision number; a revision of 0 on a client indicates no VTP updates received.

Remember that VTP domain names are case-sensitive and must match exactly; a common trick on the exam is a subtle typo.

Know that VTP clients cannot create VLANs locally; they rely on VTP servers. If VLANs are missing, always check VTP domain name and trunk status.

Commands Used in This Scenario

show interfaces trunk

Displays trunk interface status, allowed VLANs, and pruning information for all trunk ports on a Cisco switch, used to verify trunking configuration and VLAN membership.

show vlan brief

Displays a summary of all VLANs configured on the switch, including VLAN ID, name, status, and ports, used to quickly verify VLAN configuration and port assignments.

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