VTP (VLAN Trunking Protocol) is a Cisco protocol available on Cisco Catalyst switches that carries VLAN information to all other Catalyst switches running VTP in the same domain. When integrating a Cisco Meraki Switch into a Cisco VTP-enabled domain, there are cases in which the protocol can prevent the VLANs on the Cisco Meraki switch from communicating with the rest of the network.
Cisco Meraki Switch Integration
The diagrams below illustrate the integration of a Cisco Meraki Switch in a Cisco environment.
In Figure 1, the environment is running VTP with pruning enabled. VLAN 1, 2 and 3 are the VLANs configured in this network. All interlinks between switches are configured as a trunk link running the 802.1Q protocol:
Figure 1. Cisco VTP domain before Meraki integration.
In Figure 2, we are introducing a Cisco Meraki Switch between Switch 1 and Switch 2. A server is configured on VLAN 2 on the Cisco Meraki Switch. There are no devices connected on Switch 2 and no ports configured on VLAN 2 and 3 on Switch 2.
Figure 2. After Meraki integration.
VTP Propagation Changes Resulting from Integration
Because the Cisco Meraki Switch does not support VTP, it will simply be forwarding all VTP traffic. Switch 1 and Switch 2 will continue to exchange VTP messages between each other. With VTP pruning enabled, the server won’t be able to communicate with the rest of the network. Switch 1 will not send traffic for VLAN 1, 2 and 3 because those VLANs will be pruned from its trunk link toward switch 2 as illustrated below.
Figure 3. Switch 2 informs switch 1 with its VLAN information
Figure 4. Switch 1 prunes VLAN 1,2 and 3 as a result from the messages received in Figure 3.
Design and Considerations
The following design configuration solutions can be implemented to provide complete interoperability within an existing VTP domain with Cisco Meraki Switches:
- Modify the pruning-eligible list on all Cisco trunk interfaces that interconnect with Cisco Meraki Switches
- For example, never prune VLANs 1-5 and 6: switchport trunk pruning vlan except 1-5, 6
- Assign an interface on switch 2 on the same VLAN as the device on the Cisco Meraki Switch. This will ensure that VTP updates include the target VLANs that the Cisco Meraki Switch(es) require.